[GC] Port G1ElasticHeap to dragonwell

Summary: G1ElasticHeap to support heap shrink/expansion in runtime

Test Plan:
test/elastic-heap/

Reviewers:

Issue:
https://github.com/alibaba/dragonwell8/issues/46

CR:
https://github.com/alibaba/dragonwell8_hotspot/pull/12

agent/src/share/classes/sun/jvm/hotspot/gc_interface/GCCause.java

@@ -55,6 +55,8 @@ public enum GCCause {
   _g1_inc_collection_pause ("G1 Evacuation Pause"),
   _g1_humongous_allocation ("G1 Humongous Allocation"),
 
+  _g1_elastic_heap_trigger_gc("Elastic Heap triggered GC"),
+
   _last_ditch_collection ("Last ditch collection"),
   _last_gc_cause ("ILLEGAL VALUE - last gc cause - ILLEGAL VALUE");
 

make/linux/makefiles/mapfile-vers-debug

@@ -84,6 +84,15 @@ SUNWprivate_1.1 {
                 JVM_DumpAllStacks;
                 JVM_DumpThreads;
                 JVM_EnableCompiler;
+                JVM_ElasticHeapGetEvaluationMode;
+                JVM_ElasticHeapSetYoungGenCommitPercent;
+                JVM_ElasticHeapGetYoungGenCommitPercent;
+                JVM_ElasticHeapSetUncommitIHOP;
+                JVM_ElasticHeapGetUncommitIHOP;
+                JVM_ElasticHeapGetTotalYoungUncommittedBytes;
+                JVM_ElasticHeapSetSoftmxPercent;
+                JVM_ElasticHeapGetSoftmxPercent;
+                JVM_ElasticHeapGetTotalUncommittedBytes;
                 JVM_Exit;
                 JVM_FillInStackTrace;
                 JVM_FindClassFromCaller;

make/linux/makefiles/mapfile-vers-product

@@ -69,6 +69,15 @@ SUNWprivate_1.1 {
                 JVM_CurrentClassLoader;
                 JVM_CurrentLoadedClass;
                 JVM_CurrentThread;
+                JVM_ElasticHeapGetEvaluationMode;
+                JVM_ElasticHeapSetYoungGenCommitPercent;
+                JVM_ElasticHeapGetYoungGenCommitPercent;
+                JVM_ElasticHeapSetUncommitIHOP;
+                JVM_ElasticHeapGetUncommitIHOP;
+                JVM_ElasticHeapGetTotalYoungUncommittedBytes;
+                JVM_ElasticHeapSetSoftmxPercent;
+                JVM_ElasticHeapGetSoftmxPercent;
+                JVM_ElasticHeapGetTotalUncommittedBytes;
                 JVM_CurrentTimeMillis;
                 JVM_DefineClass;
                 JVM_DefineClassWithSource;

src/share/vm/gc_implementation/g1/elasticHeap.cpp

+/*
+ * Copyright (c) 2019 Alibaba Group Holding Limited. All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Alibaba designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "gc_implementation/g1/g1CollectedHeap.hpp"
+#include "gc_implementation/g1/g1CollectorPolicy.hpp"
+#include "gc_implementation/g1/elasticHeap.hpp"
+#include "gc_implementation/g1/concurrentMarkThread.hpp"
+#include "runtime/init.hpp"
+#include "runtime/javaCalls.hpp"
+
+template <bool commit, bool free>
+class RegionMemoryClosure : public HeapRegionClosure {
+private:
+  ElasticHeap* _elastic_heap;
+public:
+  RegionMemoryClosure(ElasticHeap* elastic_heap) : _elastic_heap(elastic_heap) {}
+
+  virtual bool doHeapRegion(HeapRegion* hr) {
+    if (commit) {
+      _elastic_heap->commit_region_memory(hr, true);
+    } else if (free) {
+      _elastic_heap->free_region_memory(hr);
+    } else {
+      _elastic_heap->uncommit_region_memory(hr);
+    }
+  }
+};
+
+ElasticHeapConcThread::ElasticHeapConcThread(ElasticHeap* elastic_heap) :
+    _elastic_heap(elastic_heap),
+    _uncommit_list("Free list for uncommitting regions", new MasterFreeRegionListMtSafeChecker()),
+    _commit_list("Free list for committing regions", new MasterFreeRegionListMtSafeChecker()),
+    _to_free_list("Free list for freeing old regions", new MasterFreeRegionListMtSafeChecker()),
+    _working(false),
+    _parallel_worker_threads(0),
+    _parallel_workers(NULL),
+    _should_terminate(false),
+    _has_terminated(false) {
+  set_name("ElasticHeapThread");
+  _conc_lock = new Monitor(Mutex::nonleaf, "ElasticHeapThread::_conc_lock", Mutex::_allow_vm_block_flag);
+  _working_lock = new Monitor(Mutex::nonleaf, "ElasticHeapThread::_working_lock", Mutex::_allow_vm_block_flag);
+
+  if (FLAG_IS_DEFAULT(ElasticHeapParallelWorkers)) {
+    ElasticHeapParallelWorkers = ConcGCThreads;
+  }
+
+  if (ElasticHeapParallelWorkers > 1) {
+    _parallel_worker_threads = ElasticHeapParallelWorkers;
+  }
+
+  if (_parallel_worker_threads != 0) {
+    _parallel_workers = new FlexibleWorkGang("Elastic Heap Parallel Worker Threads",
+                                             _parallel_worker_threads, false, false);
+    if (_parallel_workers == NULL) {
+      vm_exit_during_initialization("Failed necessary allocation.");
+    } else {
+      _parallel_workers->initialize_workers();
+    }
+  }
+}
+
+void ElasticHeapConcThread::start() {
+  if (!os::create_thread(this, os::cgc_thread)) {
+    vm_exit_during_initialization("Cannot create ElasticHeapConcThread. Out of system resources.");
+  }
+  Thread::start(this);
+}
+
+void ElasticHeapConcThread::wait_for_universe_init() {
+  MutexLockerEx x(_conc_lock, Mutex::_no_safepoint_check_flag);
+  while (!is_init_completed()) {
+    _conc_lock->wait(Mutex::_no_safepoint_check_flag, 100 /* ms */);
+  }
+}
+
+void ElasticHeapConcThread::sleep_before_next_cycle() {
+  MutexLockerEx x(_conc_lock, Mutex::_no_safepoint_check_flag);
+  while (!working() && !_should_terminate) {
+    // Wait for ElasticHeap::evaluate_elastic_work in safepoint to notify
+    _conc_lock->wait(Mutex::_no_safepoint_check_flag);
+  }
+}
+
+void ElasticHeapConcThread::sanity_check() {
+  if (!_uncommit_list.is_empty()) {
+    guarantee(_commit_list.is_empty(), "sanity");
+  } else if (!_commit_list.is_empty()) {
+    guarantee(_uncommit_list.is_empty(), "sanity");
+  } else {
+    guarantee(!_to_free_list.is_empty(), "sanity");
+  }
+}
+
+void ElasticHeapConcThread::do_memory_job() {
+  double start = os::elapsedTime();
+  uint commit_length = 0;
+  uint uncommit_length = 0;
+
+  RegionMemoryClosure<false, false> uncommit_cl(_elastic_heap);
+  RegionMemoryClosure<false, true> free_cl(_elastic_heap);
+
+  // We don't want a lot of page faults while accessing a lot of memory(several GB)
+  // in a very short period of time(few seconds) which may cause Java threads slow down
+  // significantly. So we will pretouch the regions after commit them.
+  RegionMemoryClosure<true, false> commit_pretouch_cl(_elastic_heap);
+
+  sanity_check();
+
+  if (!_uncommit_list.is_empty()) {
+    uncommit_length += do_memory(&_uncommit_list, &uncommit_cl);
+  }
+
+  if (!_commit_list.is_empty()) {
+    commit_length += do_memory(&_commit_list, &commit_pretouch_cl);
+  }
+
+  if (!_to_free_list.is_empty()) {
+    uncommit_length += do_memory(&_to_free_list, &free_cl);
+  }
+
+  if (PrintElasticHeapDetails) {
+    print_work_summary(uncommit_length, commit_length, start);
+  }
+}
+
+void ElasticHeapConcThread::set_working() {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+  assert(!_working, "sanity");
+  _working = true;
+}
+
+void ElasticHeapConcThread::print_work_summary(uint uncommit_length, uint commit_length, double start) {
+  assert(uncommit_length !=0 || commit_length != 0, "sanity");
+  const char* op = NULL;
+  uint list_length = 0;
+  if (uncommit_length != 0 && commit_length != 0) {
+    op = "commit/uncommit";
+    list_length = uncommit_length + commit_length;
+  } else if (uncommit_length != 0) {
+    op = "uncommit";
+    list_length = uncommit_length;
+  } else if (commit_length != 0) {
+    op = "commit";
+    list_length = commit_length;
+  } else {
+    ShouldNotReachHere();
+  }
+  size_t bytes = list_length * HeapRegion::GrainBytes;
+  gclog_or_tty->print_cr("[Elastic Heap concurrent thread: %s " SIZE_FORMAT "%s spent %.3fs(concurrent workers: %u) ]",
+    op,
+    byte_size_in_proper_unit(bytes),
+    proper_unit_for_byte_size(bytes),
+    os::elapsedTime() - start,
+    _parallel_worker_threads > 1 ? _parallel_worker_threads : 1);
+}
+
+void ElasticHeapConcThread::run() {
+  wait_for_universe_init();
+
+  while (!_should_terminate) {
+    // wait until working is set.
+    sleep_before_next_cycle();
+    if (_should_terminate) {
+      break;
+    }
+
+    assert(working(), "sanity");
+
+    do_memory_job();
+
+    // Thread work is done by now
+    {
+      MutexLockerEx x(_working_lock, Mutex::_no_safepoint_check_flag);
+      clear_working();
+      _working_lock->notify_all();
+    }
+  }
+
+  {
+    MutexLockerEx mu(Terminator_lock,
+      Mutex::_no_safepoint_check_flag);
+    _has_terminated = true;
+    Terminator_lock->notify();
+  }
+}
+
+void ElasticHeapConcThread::stop() {
+  {
+    MutexLockerEx ml(Terminator_lock);
+    _should_terminate = true;
+  }
+
+  {
+    MutexLockerEx ml(_conc_lock, Mutex::_no_safepoint_check_flag);
+    _conc_lock->notify();
+  }
+  {
+    MutexLockerEx ml(Terminator_lock);
+    while (!_has_terminated) {
+      Terminator_lock->wait();
+    }
+  }
+}
+
+uint ElasticHeapConcThread::do_memory(FreeRegionList* list, HeapRegionClosure* cl) {
+  if (_parallel_worker_threads != 0) {
+    par_work_on_regions(list, cl);
+  } else {
+    FreeRegionListIterator iter(list);
+    while (iter.more_available()) {
+      HeapRegion* hr = iter.get_next();
+      cl->doHeapRegion(hr);
+    }
+  }
+  return list->length();
+}
+
+class ElasticHeapParTask : public AbstractGangTask {
+private:
+  FreeRegionList* _list;
+  HeapRegionClosure* _cl;
+  uint _n_workers;
+  uint _num_regions_per_worker;
+public:
+  ElasticHeapParTask(FreeRegionList* list, HeapRegionClosure* cl, uint n_workers)
+    : AbstractGangTask("Elastic Heap memory commit/uncommit task"),
+      _list(list), _cl(cl), _n_workers(n_workers) {
+    if ((list->length() % n_workers) == 0 ) {
+      _num_regions_per_worker = list->length() / _n_workers;
+    } else {
+      _num_regions_per_worker = list->length() / _n_workers + 1;
+    }
+  }
+
+  void work(uint worker_id) {
+    uint skipped = 0;
+    FreeRegionListIterator iter(_list);
+    while (iter.more_available()) {
+      if (skipped == _num_regions_per_worker * worker_id) {
+        break;
+      }
+      iter.get_next();
+      skipped++;
+    }
+    uint index = 0;
+    while (iter.more_available()) {
+      if (index == _num_regions_per_worker) {
+        break;
+      }
+      HeapRegion* hr = iter.get_next();
+      _cl->doHeapRegion(hr);
+      index++;
+    }
+  }
+};
+
+void ElasticHeapConcThread::par_work_on_regions(FreeRegionList* list, HeapRegionClosure* cl) {
+  _parallel_workers->set_active_workers((int)_parallel_worker_threads);
+  ElasticHeapParTask task(list, cl, _parallel_worker_threads);
+  _parallel_workers->run_task(&task);
+}
+
+uint ElasticHeapConcThread::total_unavaiable_regions() {
+  return _uncommit_list.length() + _commit_list.length() + _to_free_list.length();
+}
+
+volatile bool ElasticHeapTimer::_should_terminate = false;
+JavaThread* ElasticHeapTimer::_thread = NULL;
+Monitor*    ElasticHeapTimer::_monitor = NULL;
+
+bool ElasticHeapTimer::has_error(TRAPS, const char* error) {
+  if (HAS_PENDING_EXCEPTION) {
+    tty->print_cr(error);
+    java_lang_Throwable::print(PENDING_EXCEPTION, tty);
+    tty->cr();
+    CLEAR_PENDING_EXCEPTION;
+    return true;
+  } else {
+    return false;
+  }
+}
+
+void ElasticHeapTimer::start() {
+  _monitor = new Monitor(Mutex::nonleaf, "ElasticHeapTimer::_monitor", Mutex::_allow_vm_block_flag);
+
+  EXCEPTION_MARK;
+  Klass* k = SystemDictionary::resolve_or_fail(vmSymbols::java_lang_Thread(), true, CHECK);
+  instanceKlassHandle klass (THREAD, k);
+  instanceHandle thread_oop = klass->allocate_instance_handle(CHECK);
+
+  const char thread_name[] = "Elastic Heap timer";
+  Handle string = java_lang_String::create_from_str(thread_name, CHECK);
+
+  // Initialize thread_oop to put it into the system threadGroup
+  Handle thread_group (THREAD, Universe::system_thread_group());
+  JavaValue result(T_VOID);
+  JavaCalls::call_special(&result, thread_oop,
+                       klass,
+                       vmSymbols::object_initializer_name(),
+                       vmSymbols::threadgroup_string_void_signature(),
+                       thread_group,
+                       string,
+                       THREAD);
+  if (has_error(THREAD, "Exception in VM (ElasticHeapTimer::start) : ")) {
+    vm_exit_during_initialization("Cannot create ElasticHeap timer thread.");
+    return;
+  }
+
+  KlassHandle group(THREAD, SystemDictionary::ThreadGroup_klass());
+  JavaCalls::call_special(&result,
+                        thread_group,
+                        group,
+                        vmSymbols::add_method_name(),
+                        vmSymbols::thread_void_signature(),
+                        thread_oop,             // ARG 1
+                        THREAD);
+  if (has_error(THREAD, "Exception in VM (ElasticHeapTimer::start) : ")) {
+    vm_exit_during_initialization("Cannot create ElasticHeap timer thread.");
+    return;
+  }
+
+  {
+    MutexLocker mu(Threads_lock);
+    _thread = new JavaThread(&ElasticHeapTimer::timer_thread_entry);
+    if (_thread == NULL || _thread->osthread() == NULL) {
+      vm_exit_during_initialization("Cannot create ElasticHeap timer thread. Out of system resources.");
+    }
+
+    java_lang_Thread::set_thread(thread_oop(), _thread);
+    java_lang_Thread::set_daemon(thread_oop());
+    _thread->set_threadObj(thread_oop());
+    Threads::add(_thread);
+    Thread::start(_thread);
+  }
+}
+
+void ElasticHeapTimer::timer_thread_entry(JavaThread* thread, TRAPS) {
+  while(!_should_terminate) {
+    assert(!SafepointSynchronize::is_at_safepoint(), "Elastic Heap timer thread is a JavaThread");
+    G1CollectedHeap::heap()->elastic_heap()->check_to_trigger_ygc();
+
+    MutexLockerEx x(_monitor);
+    if (_should_terminate) {
+      break;
+    }
+    _monitor->wait(false /* no_safepoint_check */, 200);
+  }
+}
+
+void ElasticHeapTimer::stop() {
+  _should_terminate = true;
+  {
+    MutexLockerEx ml(_monitor, Mutex::_no_safepoint_check_flag);
+    _monitor->notify();
+  }
+}
+
+ElasticHeapGCStats::ElasticHeapGCStats(ElasticHeap* elas, G1CollectedHeap* g1h) :
+    _elas(elas),
+    _g1h(g1h),
+    _recent_ygc_normalized_interval_ms(new TruncatedSeq(GC_INTERVAL_SEQ_LENGTH)),
+    _last_gc_end_timestamp_s(0.0),
+    _last_initial_mark_timestamp_s(0.0),
+    _last_gc_mixed(false),
+    _mixed_gc_finished(false),
+    _need_mixed_gc(false),
+    _last_initial_mark_interval_s(0.0),
+    _last_initial_mark_non_young_bytes(0),
+    _last_normalized_eden_consumed_length(0) {
+}
+
+void ElasticHeapGCStats::track_gc_start(bool full_gc) {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  double now = os::elapsedTime();
+
+  if (full_gc) {
+    reset_mixed_gc_info();
+  } else {
+    if (_g1h->g1_policy()->last_young_gc()) {
+      // The last young gc after conc-mark and before mixed gc(if needed)
+      // We treat it as part of mixed GCs
+      _last_gc_mixed = true;
+    } else if (_g1h->g1_policy()->gcs_are_young()) {
+      // Regular young GC
+      if (_last_gc_mixed) {
+        _mixed_gc_finished = true;
+        _last_gc_mixed = false;
+      }
+    } else {
+      // Mixed GC
+      _last_gc_mixed = true;
+    }
+  }
+
+  if (_g1h->g1_policy()->during_initial_mark_pause()) {
+    _last_initial_mark_interval_s = now - _last_initial_mark_timestamp_s;
+    _last_initial_mark_timestamp_s = now;
+    _last_initial_mark_non_young_bytes = _g1h->non_young_capacity_bytes();
+  }
+
+  double gc_interval_s = now - _last_gc_end_timestamp_s;
+
+  uint available_young_length = _elas->calculate_young_list_desired_max_length() -
+                                _elas->overlapped_young_regions_with_old_gen();
+
+  uint eden_consumed_length = _g1h->young_list()->length() - _g1h->young_list()->survivor_length();
+  if (eden_consumed_length == 0) {
+    // Java threads didn't consumed any eden regions before this gc
+    if ((gc_interval_s * MILLIUNITS) > (double)ElasticHeapPeriodicYGCIntervalMillis) {
+      // If the interval is long enough, we treat it a long normalized interval
+      _recent_ygc_normalized_interval_ms->add(ElasticHeapPeriodicYGCIntervalMillis * GC_INTERVAL_SEQ_LENGTH);
+      _last_normalized_eden_consumed_length = available_young_length;
+    }
+  } else {
+    // This interval between 2 GCs will be normalized to full young length
+    double normalized_interval = gc_interval_s * (double)available_young_length / (double)eden_consumed_length;
+    _recent_ygc_normalized_interval_ms->add(normalized_interval * MILLIUNITS);
+    _last_normalized_eden_consumed_length = available_young_length;
+  }
+}
+
+bool ElasticHeapGCStats::check_mixed_gc_finished() {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  if (!_mixed_gc_finished) {
+    return false;
+  }
+  _mixed_gc_finished = false;
+  _need_mixed_gc = false;
+  return true;
+}
+
+ElasticHeapSetting::ElasticHeapSetting(ElasticHeap* elas, G1CollectedHeap* g1h) :
+    _elas(elas),
+    _g1h(g1h),
+    _young_percent(0),
+    _uncommit_ihop(0),
+    _softmx_percent(0) {
+}
+
+ElasticHeap::ErrorType ElasticHeapSetting::change_young_percent(uint young_percent, bool& trigger_gc) {
+  ElasticHeap::ErrorType error_type = ElasticHeap::NoError;
+  if (ignore_arg(young_percent, _young_percent)) {
+    // Do nothing
+  } else if (!((young_percent >= ElasticHeapMinYoungCommitPercent && young_percent <= 100) ||
+                young_percent == 0)) {
+    error_type = ElasticHeap::IllegalYoungPercent;
+  } else if (can_change_young_percent(young_percent)) {
+    error_type = ElasticHeap::NoError;
+    trigger_gc = true;
+    _young_percent = young_percent;
+  } else {
+    error_type = ElasticHeap::GCTooFrequent;
+  }
+  return error_type;
+}
+
+ElasticHeap::ErrorType ElasticHeapSetting::change_uncommit_ihop(uint uncommit_ihop, bool& trigger_gc) {
+  if (!ignore_arg(uncommit_ihop, _uncommit_ihop)) {
+    _uncommit_ihop = uncommit_ihop;
+    _elas->check_to_initate_conc_mark();
+    trigger_gc = true;
+  }
+  return ElasticHeap::NoError;
+}
+
+ElasticHeap::ErrorType ElasticHeapSetting::change_softmx_percent(uint softmx_percent, bool& trigger_gc) {
+  if (!ignore_arg(softmx_percent, _softmx_percent)) {
+    _softmx_percent = softmx_percent;
+    _elas->check_to_initate_conc_mark();
+    trigger_gc = true;
+  }
+  return ElasticHeap::NoError;
+}
+
+ElasticHeap::EvaluationMode ElasticHeapSetting::target_evaluation_mode(uint young_percent,
+                                       uint uncommit_ihop,
+                                       uint softmx_percent) {
+  assert(!((young_percent != ignore_arg() || uncommit_ihop != ignore_arg()) && softmx_percent != ignore_arg()), "sanity");
+  if (young_percent != ignore_arg() || uncommit_ihop != ignore_arg()) {
+    return ElasticHeap::GenerationLimitMode;
+  } else if (softmx_percent != ignore_arg()) {
+    return ElasticHeap::SoftmxMode;
+  } else {
+    ShouldNotReachHere();
+  }
+}
+
+ElasticHeap::ErrorType ElasticHeapSetting::process_arg(uint young_percent,
+                                                       uint uncommit_ihop,
+                                                       uint softmx_percent,
+                                                       bool& trigger_gc) {
+  if (_elas->conflict_mode(target_evaluation_mode(young_percent, uncommit_ihop, softmx_percent))) {
+    return ElasticHeap::IllegalMode;
+  }
+
+  ElasticHeap::ErrorType error_type = ElasticHeap::NoError;
+
+  error_type = change_young_percent(young_percent, trigger_gc);
+  if (error_type != ElasticHeap::NoError) {
+    return error_type;
+  }
+
+  error_type = change_uncommit_ihop(uncommit_ihop, trigger_gc);
+  assert(error_type == ElasticHeap::NoError, "sanity");
+
+  error_type = change_softmx_percent(softmx_percent, trigger_gc);
+  assert(error_type == ElasticHeap::NoError, "sanity");
+
+  return ElasticHeap::NoError;
+}
+
+bool ElasticHeapSetting::can_change_young_percent(uint percent) {
+  if (percent == 0) {
+    return true;
+  }
+  assert(percent >= ElasticHeapMinYoungCommitPercent && percent <= 100, "sanity");
+  uint target_max_young_length = _elas->max_young_length() * percent / 100;
+
+  // Check if ihop threashold will overlap young generation
+  uint ihop_length = (uint)ceil((double)_g1h->num_regions() * InitiatingHeapOccupancyPercent / 100);
+  int overlap_length = ihop_length + _elas->g1_reserve_regions() +
+                       _elas->max_young_length() - _g1h->num_regions();
+  if (overlap_length > 0) {
+    if ((uint)overlap_length >= target_max_young_length) {
+      // No available young length at all
+      return false;
+    }
+    target_max_young_length -= (uint)overlap_length;
+  }
+
+  double last_interval = _elas->stats()->last_normalized_interval();
+  double target_interval = last_interval *
+                           (target_max_young_length * SurvivorRatio / (SurvivorRatio + 1)) /
+                           _elas->stats()->last_normalized_eden_consumed_length();
+  if ((target_max_young_length < _elas->calculate_young_list_desired_max_length()) &&
+      (last_interval < ElasticHeapYGCIntervalMinMillis ||
+      target_interval < ElasticHeapYGCIntervalMinMillis)) {
+    // Last GC interval too small or target GC interval too small
+    // We cannot do shrink
+    // Expansion is always ok
+    return false;
+  }
+  return true;
+}
+
+ElasticHeap::ElasticHeap(G1CollectedHeap* g1h) : _g1h(g1h),
+    _stats(NULL),
+    _setting(NULL),
+    _orig_ihop(0),
+    _orig_min_desired_young_length(0),
+    _orig_max_desired_young_length(0),
+    _in_conc_cycle(false),
+    _conc_thread(NULL),
+    _configure_setting_lock(0),
+    _heap_capacity_changed(false) {
+
+  _orig_max_desired_young_length = _g1h->g1_policy()->_young_gen_sizer->max_desired_young_length();
+  _orig_min_desired_young_length = _g1h->g1_policy()->_young_gen_sizer->min_desired_young_length();
+  _orig_ihop = InitiatingHeapOccupancyPercent;
+
+  _conc_thread = new ElasticHeapConcThread(this);
+  _conc_thread->start();
+
+  _stats = new ElasticHeapGCStats(this, g1h);
+  _setting = new ElasticHeapSetting(this, g1h);
+
+  _evaluators[InactiveMode] = new RecoverEvaluator(this);
+  _evaluators[PeriodicUncommitMode] = new PeriodicEvaluator(this);
+  _evaluators[GenerationLimitMode] = new GenerationLimitEvaluator(this);
+  _evaluators[SoftmxMode] = new SoftmxEvaluator(this);
+}
+
+void ElasticHeap::destroy() {
+  _conc_thread->stop();
+  ElasticHeapTimer::stop();
+}
+
+void ElasticHeap::check_to_initate_conc_mark() {
+  if (_g1h->concurrent_mark()->cmThread()->during_cycle()) {
+    return;
+  }
+  if (_stats->need_mixed_gc()) {
+    // G1 conc-mark cycle already started
+    return;
+  }
+  if (PrintElasticHeapDetails) {
+    gclog_or_tty->print_cr("(Elastic Heap triggers G1 concurrent mark)");
+  }
+  _g1h->g1_policy()->set_initiate_conc_mark_if_possible();
+  _stats->set_need_mixed_gc(true);
+}
+
+void ElasticHeap::check_to_trigger_ygc() {
+  if (evaluation_mode() == InactiveMode) {
+    return;
+  }
+
+  double now = os::elapsedTime();
+  double secs_since_last_gc = now - _stats->last_gc_end_timestamp_s();
+
+  bool trigger_gc = false;
+  if (_stats->need_mixed_gc() &&
+      (secs_since_last_gc * MILLIUNITS) > ElasticHeapEagerMixedGCIntervalMillis) {
+    // If already in conc-mark/mixed gc phase, make sure mixed gc will happen promptly
+    trigger_gc = true;
+  }
+  if (evaluation_mode() == PeriodicUncommitMode) {
+    if (ElasticHeapPeriodicYGCIntervalMillis != 0 &&
+        ((secs_since_last_gc * MILLIUNITS) > ElasticHeapPeriodicYGCIntervalMillis * 5)) {
+      // In PeriodicUncommitMode if GC interval is more than
+      // 5 times of ElasticHeapPeriodicYGCIntervalMillis, we will trigger a GC
+      trigger_gc = true;
+    }
+    uint millis_since_last_init_mark = (now - _stats->last_initial_mark_timestamp_s()) * MILLIUNITS;
+    if (ElasticHeapPeriodicInitialMarkIntervalMillis != 0 &&
+        (millis_since_last_init_mark > ElasticHeapPeriodicInitialMarkIntervalMillis)) {
+      // Check if we need to start a conc-mark cycle
+      check_to_initate_conc_mark();
+      trigger_gc = true;
+    }
+  }
+
+  if (trigger_gc) {
+    // Invoke GC
+    Universe::heap()->collect(GCCause::_g1_elastic_heap_trigger_gc);
+  }
+}
+
+uint ElasticHeap::num_unavailable_regions() {
+  assert_heap_locked_or_at_safepoint(true /* should_be_vm_thread */);
+  return _g1h->_hrm.num_uncommitted_regions() + _conc_thread->total_unavaiable_regions();
+}
+
+int ElasticHeap::young_commit_percent() const {
+  if (_setting->young_percent_set()) {
+    // Specify by jcmd/mxbean
+    return _setting->young_percent();
+  } else {
+    uint uncommitted_young_length = _g1h->_hrm.num_uncommitted_regions() + _conc_thread->uncommit_list()->length();
+    return (max_young_length() - uncommitted_young_length) * 100 / max_young_length();
+  }
+}
+
+jlong ElasticHeap::young_uncommitted_bytes() const {
+  uint uncommitted_young_length = _g1h->_hrm.num_uncommitted_regions() + _conc_thread->uncommit_list()->length();
+  return (jlong)uncommitted_young_length << HeapRegion::LogOfHRGrainBytes;
+}
+
+int ElasticHeap::softmx_percent() const {
+  return _g1h->num_regions() * 100 / _g1h->max_regions();
+}
+
+jlong ElasticHeap::uncommitted_bytes() const {
+  return (jlong)(_g1h->max_regions() - _g1h->num_regions()) * HeapRegion::GrainBytes;
+}
+
+int ElasticHeap::uncommit_ihop() const {
+  return _setting->uncommit_ihop();
+}
+
+uint ElasticHeap::overlapped_young_regions_with_old_gen() {
+  assert(Universe::heap()->is_gc_active(), "should only be called during gc");
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  uint non_young_length = (uint)((double)_g1h->non_young_capacity_bytes() / HeapRegion::GrainBytes + 1);
+  int regions = non_young_length + _g1h->g1_policy()->_reserve_regions +
+                max_young_length() - _g1h->num_regions();
+  if (regions < 0) {
+    regions = 0;
+  }
+  return regions;
+}
+
+ElasticHeap::EvaluationMode ElasticHeap::evaluation_mode() const {
+  if (_setting->softmx_percent_set()) {
+    return SoftmxMode;
+  } else if (_setting->generation_limit_set()) {
+    return GenerationLimitMode;
+  } else if (ElasticHeapPeriodicUncommit &&
+             !(ElasticHeapPeriodicYGCIntervalMillis == 0 &&
+               ElasticHeapPeriodicInitialMarkIntervalMillis == 0)) {
+    return PeriodicUncommitMode;
+  } else {
+    return InactiveMode;
+  }
+}
+
+void ElasticHeap::uncommit_region_memory(HeapRegion* hr) {
+  _g1h->_hrm.uncommit_region_memory(hr->hrm_index());
+}
+
+void ElasticHeap::commit_region_memory(HeapRegion* hr, bool pretouch) {
+  _g1h->_hrm.commit_region_memory(hr->hrm_index());
+  if (pretouch) {
+    os::pretouch_memory((char*)hr->bottom(), (char*)hr->bottom() + HeapRegion::GrainBytes);
+  }
+}
+
+void ElasticHeap::free_region_memory(HeapRegion* hr) {
+  _g1h->_hrm.free_region_memory(hr->hrm_index());
+}
+
+bool ElasticHeap::conflict_mode(EvaluationMode target_mode) {
+  assert (target_mode != InactiveMode, "sanity");
+  EvaluationMode mode = evaluation_mode();
+  if (mode == InactiveMode) {
+    return false;
+  } else {
+    return (target_mode != mode);
+  }
+}
+
+void ElasticHeap::prepare_in_gc_start() {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  record_gc_start();
+  check_end_of_previous_conc_cycle();
+}
+
+void ElasticHeap::record_gc_start(bool full_gc) {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  _stats->track_gc_start(full_gc);
+}
+
+void ElasticHeap::record_gc_end() {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  _stats->set_last_gc_end_timestamp_s(os::elapsedTime());
+}
+
+void ElasticHeap::start_conc_cycle() {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  guarantee(!in_conc_cycle(), "sanity");
+  guarantee(!_conc_thread->working(), "sanity");
+  guarantee(_conc_thread->total_unavaiable_regions() != 0, "sanity");
+  _in_conc_cycle = true;
+}
+
+void ElasticHeap::end_conc_cycle() {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  guarantee(in_conc_cycle(), "sanity");
+  guarantee(!_conc_thread->working(), "sanity");
+  guarantee(_conc_thread->total_unavaiable_regions() == 0, "sanity");
+  _in_conc_cycle = false;
+}
+
+void ElasticHeap::move_regions_back_to_hrm() {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  _conc_thread->sanity_check();
+
+  bool need_update_expanded_size = false;
+  if (!_conc_thread->uncommit_list()->is_empty()) {
+    _g1h->_hrm.move_to_uncommitted_list(_conc_thread->uncommit_list());
+  }
+
+  if (!_conc_thread->commit_list()->is_empty()) {
+    _g1h->_hrm.move_to_free_list(_conc_thread->commit_list());
+    need_update_expanded_size = true;
+  }
+
+  if (!_conc_thread->to_free_list()->is_empty()) {
+    _g1h->_hrm.move_to_free_list(_conc_thread->to_free_list());
+  }
+
+  if (need_update_expanded_size) {
+    update_expanded_heap_size();
+  }
+}
+
+void ElasticHeap::finish_conc_cycle() {
+  assert(!_conc_thread->working(), "Precondition");
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  move_regions_back_to_hrm();
+  end_conc_cycle();
+
+  if (PrintElasticHeapDetails) {
+    gclog_or_tty->print("(Elastic Heap concurrent cycle ends)\n");
+  }
+}
+
+void ElasticHeap::check_end_of_previous_conc_cycle() {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  if (!in_conc_cycle()) {
+    // Not in a concurrent cycle, do nothing
+    return;
+  }
+
+  if (_conc_thread->working()) {
+    // ElasticHeapThread is still working on commit/uncommit
+    assert(in_conc_cycle(), "sanity");
+    return;
+  }
+
+  finish_conc_cycle();
+}
+
+void ElasticHeap::wait_for_conc_cycle_end() {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+  assert(_g1h->full_collection(), "Precondition");
+
+  if (in_conc_cycle()) {
+    wait_for_conc_thread_working_done(false);
+    finish_conc_cycle();
+  }
+}
+
+void ElasticHeap::wait_to_recover() {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+  assert(_g1h->full_collection(), "Precondition");
+
+  wait_for_conc_cycle_end();
+
+  _g1h->_hrm.recover_uncommitted_regions();
+
+  assert(ElasticHeapPeriodicUncommit, "sanity");
+  update_desired_young_length(0);
+
+  if (PrintElasticHeapDetails) {
+    gclog_or_tty->print_cr("[Elastic Heap recovers]");
+  }
+}
+
+bool ElasticHeap::is_gc_to_resize_young_gen() {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  return Universe::heap()->gc_cause() == GCCause::_g1_elastic_heap_trigger_gc && _setting->young_percent_set();
+}
+
+bool ElasticHeap::can_turn_on_periodic_uncommit() {
+  return !in_conc_cycle() && !_setting->softmx_percent_set() && !_setting->generation_limit_set();
+}
+
+void ElasticHeap::update_expanded_heap_size() {
+  assert(Universe::heap()->is_gc_active(), "should only be called during gc");
+  assert_at_safepoint(true /* should_be_vm_thread */);
+  assert(_conc_thread->total_unavaiable_regions() == 0, "sanity");
+
+  if (heap_capacity_changed()) {
+    // Complete heap expanding in softmx percent mode
+    uint committed_num = _g1h->max_regions() -_g1h->_hrm.num_uncommitted_regions();
+    assert(committed_num == _g1h->num_regions(), "sanity");
+    change_heap_capacity(committed_num);
+  } else {
+    update_desired_young_length(_g1h->_hrm.num_uncommitted_regions());
+  }
+}
+
+void ElasticHeap::perform() {
+  assert(Universe::heap()->is_gc_active(), "should only be called during gc");
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  if (!in_conc_cycle()) {
+    // Do evaluation whether to resize or not, to start the new conc cycle
+    evaluate_elastic_work();
+  }
+
+  record_gc_end();
+}
+
+void ElasticHeap::evaluate_elastic_work() {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  _evaluators[evaluation_mode()]->evaluate();
+
+  try_starting_conc_cycle();
+}
+
+void ElasticHeap::update_desired_young_length(uint unavailable_young_length) {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  assert(unavailable_young_length ==
+         (_g1h->_hrm.num_uncommitted_regions() + _conc_thread->uncommit_list()->length()),
+         "sanity");
+
+  uint max_young_length = _orig_max_desired_young_length - unavailable_young_length;
+  _g1h->g1_policy()->_young_gen_sizer->resize_max_desired_young_length(max_young_length);
+  if (_orig_min_desired_young_length > max_young_length) {
+    _g1h->g1_policy()->_young_gen_sizer->resize_min_desired_young_length(max_young_length);
+  } else {
+    _g1h->g1_policy()->_young_gen_sizer->resize_min_desired_young_length(_orig_min_desired_young_length);
+  }
+}
+
+void ElasticHeap::set_heap_capacity_changed(uint num) {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  if (num != _g1h->max_regions()) {
+    _heap_capacity_changed = true;
+    assert(evaluation_mode() == SoftmxMode, "Precondition");
+  } else {
+    _heap_capacity_changed = false;
+  }
+}
+
+void ElasticHeap::change_heap_capacity(uint target_heap_regions) {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  // Change the heap capacity
+  set_heap_capacity_changed(target_heap_regions);
+  guarantee(_g1h->num_regions() == target_heap_regions, "sanity");
+
+  // Change IHOP and young size
+  InitiatingHeapOccupancyPercent = _orig_ihop;
+  _g1h->g1_policy()->_young_gen_sizer->resize_min_desired_young_length(_orig_min_desired_young_length);
+  _g1h->g1_policy()->_young_gen_sizer->resize_max_desired_young_length(_orig_max_desired_young_length);
+
+  size_t target_heap_capacity = target_heap_regions * HeapRegion::GrainBytes;
+  size_t target_conc_threshold = target_heap_capacity * InitiatingHeapOccupancyPercent / 100;
+  size_t non_young_bytes = _g1h->non_young_capacity_bytes();
+
+  if ((non_young_bytes + target_heap_capacity * ElasticHeapOldGenReservePercent / 100) >
+      target_conc_threshold) {
+    // We don't have ElasticHeapOldGenReservePercent for old gen to grow
+    // So need to adjust the ihop
+    InitiatingHeapOccupancyPercent = (uint)ceil((double)(non_young_bytes + target_heap_capacity * 5
+                                                 / 100) * 100 / target_heap_capacity);
+  }
+
+  assert(InitiatingHeapOccupancyPercent <  100 && InitiatingHeapOccupancyPercent > 0, "sanity");
+
+  assert(target_heap_regions == _g1h->num_regions(), "sanity");
+  _g1h->g1_policy()->record_new_heap_size(target_heap_regions);
+
+  if (_g1h->num_regions() == _g1h->max_regions()) {
+    InitiatingHeapOccupancyPercent = _orig_ihop;
+  } else {
+    change_young_size_for_softmx();
+  }
+}
+
+void ElasticHeap::change_young_size_for_softmx() {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  // Resize min/max young length according to softmx percent
+  uint softmx_percent = setting()->softmx_percent();
+  assert(softmx_percent > 0 && softmx_percent < 100, "sanity");
+  uint min_desired_young_length = (uint)ceil((double)_orig_min_desired_young_length * softmx_percent / 100);
+  uint max_desired_young_length = (uint)ceil((double)_orig_max_desired_young_length * softmx_percent / 100);
+  assert(min_desired_young_length > 0 && max_desired_young_length > 0, "sanity");
+  _g1h->g1_policy()->_young_gen_sizer->resize_min_desired_young_length(min_desired_young_length);
+  _g1h->g1_policy()->_young_gen_sizer->resize_max_desired_young_length(max_desired_young_length);
+
+  // If min desired young length is too large, we need to shrink
+  assert((InitiatingHeapOccupancyPercent + (g1_reserve_factor() * 100)) < 100, "sanity");
+  uint safe_min_desired_young_length = _g1h->num_regions() * (100 - InitiatingHeapOccupancyPercent - (g1_reserve_factor() * 100)) / 100;
+  if (_g1h->g1_policy()->_young_gen_sizer->min_desired_young_length() > safe_min_desired_young_length) {
+    _g1h->g1_policy()->_young_gen_sizer->resize_min_desired_young_length(safe_min_desired_young_length);
+  }
+}
+
+void ElasticHeap::try_starting_conc_cycle() {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  if (_conc_thread->total_unavaiable_regions() == 0) {
+    return;
+  }
+
+  {
+    MutexLockerEx ml(_conc_thread->conc_lock(), Mutex::_no_safepoint_check_flag);
+    start_conc_cycle();
+    _conc_thread->set_working();
+    // Notify thread to do the work
+    _conc_thread->conc_lock()->notify();
+  }
+
+  if (PrintElasticHeapDetails) {
+    gclog_or_tty->print("(Elastic Heap concurrent cycle starts due to %s)", to_string(evaluation_mode()));
+  }
+}
+
+bool ElasticHeap::enough_free_regions_to_uncommit(uint num_regions_to_uncommit) {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  if (_g1h->g1_policy()->_free_regions_at_end_of_collection <= _g1h->g1_policy()->_reserve_regions) {
+    // Free regions already less than G1 reserve
+    return false;
+  }
+  if (num_regions_to_uncommit >=
+      (_g1h->g1_policy()->_free_regions_at_end_of_collection -
+       _g1h->g1_policy()->_reserve_regions)) {
+    // No enough free regions excluding G1 reserve
+    return false;
+  }
+  return true;
+}
+
+void ElasticHeap::resize_young_length(uint target_length) {
+  assert(Universe::heap()->is_gc_active(), "should only be called during gc");
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  uint target_uncommitted_length = max_young_length() - target_length;
+  uint old_num_uncommitted = _g1h->_hrm.num_uncommitted_regions();
+
+  if (old_num_uncommitted == target_uncommitted_length) {
+    // No more regions need to be commit/uncommit
+    return;
+  }
+  assert(_conc_thread->conc_lock()->owner() == NULL, "Precondition");
+
+  uint new_uncommitted_length = 0;
+  if (old_num_uncommitted < target_uncommitted_length) {
+    // Shrink young gen
+    new_uncommitted_length = target_uncommitted_length - old_num_uncommitted;
+
+    if (!enough_free_regions_to_uncommit(new_uncommitted_length)) {
+      if (_setting->young_percent_set()) {
+        _setting->set_young_percent((max_young_length() - _g1h->_hrm.num_uncommitted_regions()) * 100 / max_young_length());
+      }
+      return;
+    }
+    // Move regions out of free list
+    uncommit_regions(new_uncommitted_length);
+    update_desired_young_length(target_uncommitted_length);
+  } else {
+    // Expand young gen
+    assert(old_num_uncommitted > target_uncommitted_length, "sanity");
+    // Move regions out of uncommitted young list
+    commit_regions(old_num_uncommitted - target_uncommitted_length);
+  }
+}
+
+void ElasticHeap::uncommit_regions(uint num) {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  guarantee(_conc_thread->uncommit_list()->is_empty() && _conc_thread->commit_list()->is_empty(), "sanity");
+
+  _g1h->_hrm.prepare_uncommit_regions(_conc_thread->uncommit_list(), num);
+}
+
+void ElasticHeap::commit_regions(uint num) {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  guarantee(_conc_thread->uncommit_list()->is_empty() && _conc_thread->commit_list()->is_empty(), "sanity");
+
+  _g1h->_hrm.prepare_commit_regions(_conc_thread->commit_list(), num);
+}
+
+uint ElasticHeap::max_available_survivor_regions() {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  // In elastic heap initiated gc, we need to make sure the survivor after gc less than the target max young length
+  uint young_percent = _setting->young_percent();
+  if (_setting->young_percent() == 0) {
+    return max_young_length();
+  } else {
+    assert(young_percent >= ElasticHeapMinYoungCommitPercent && young_percent <= 100, "sanity");
+    return (young_percent * max_young_length() / 100) - 1;
+  }
+}
+
+void ElasticHeap::wait_for_conc_thread_working_done(bool safepointCheck) {
+  if (_conc_thread->working()) {
+    // Get the lock to wait for the finish of memory work
+    if (safepointCheck) {
+      assert(!Thread::current()->is_VM_thread(), "Should not be called in VM thread, either called from JCMD or MXBean");
+      MutexLockerEx x(_conc_thread->working_lock());
+      // Wait for conc thread to wake
+      while (_conc_thread->working()) {
+        _conc_thread->working_lock()->wait();
+      }
+    } else {
+      assert(_g1h->full_collection(), "Precondition");
+      assert_at_safepoint(true /* should_be_vm_thread */);
+      MutexLockerEx x(_conc_thread->working_lock(), Mutex::_no_safepoint_check_flag);
+      // Wait for conc thread to wake
+      while (_conc_thread->working()) {
+        _conc_thread->working_lock()->wait(Mutex::_no_safepoint_check_flag);
+      }
+    }
+  }
+}
+
+uint ElasticHeap::ignore_arg() {
+  return ElasticHeapSetting::ignore_arg();
+}
+
+class ElasticHeapConfigureSettingLock : public StackObj {
+public:
+  ElasticHeapConfigureSettingLock(volatile int* lock) : _lock(lock) {
+    if (*lock == 1) {
+      _locked = false;
+    }
+    _locked = ((int) Atomic::cmpxchg(1, lock, 0) == 0);
+  }
+  ~ElasticHeapConfigureSettingLock() {
+    if (_locked) {
+      *_lock = 0;
+    }
+  }
+  bool locked() { return _locked; }
+private:
+  volatile int*   _lock;
+  bool            _locked;
+};
+
+ElasticHeap::ErrorType ElasticHeap::configure_setting(uint young_percent, uint uncommit_ihop, uint softmx_percent) {
+  // Called from Java thread or listener thread
+  assert(!Thread::current()->is_VM_thread(), "Should not be called in VM thread, either called from JCMD or MXBean");
+  assert(JavaThread::current()->thread_state() == _thread_in_vm, "Should be in VM state");
+
+  ElasticHeapConfigureSettingLock lock(&_configure_setting_lock);
+  if (!lock.locked()) {
+    return HeapAdjustInProgress;
+  }
+
+  if (_conc_thread->working()) {
+    // If the memory work is not done, return error
+    return HeapAdjustInProgress;
+  }
+
+  bool trigger_gc = false;
+  ElasticHeap::ErrorType error_type = _setting->process_arg(young_percent, uncommit_ihop,
+                                                           softmx_percent, trigger_gc);;
+
+  if (error_type != NoError) {
+    return error_type;
+  }
+
+  if (!trigger_gc) {
+    return NoError;
+  }
+
+  assert(!_conc_thread->working(), "sanity");
+
+  // Invoke GC
+  Universe::heap()->collect(GCCause::_g1_elastic_heap_trigger_gc);
+  // Need to handle the scenario that gc is not successfully triggered
+
+  wait_for_conc_thread_working_done(true);
+  guarantee(!_conc_thread->working(), "sanity");
+
+  return NoError;
+}
+
+bool ElasticHeap::ready_to_uncommit_after_mixed_gc() {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  if (!_stats->check_mixed_gc_finished()) {
+    return false;
+  }
+
+  if ((_stats->last_initial_mark_interval_s() * MILLIUNITS) <
+       ElasticHeapInitialMarkIntervalMinMillis) {
+    // If last 2 initial marks are too close, do not uncommit memory
+    return false;
+  }
+  return true;
+}
+
+void ElasticHeap::uncommit_old_gen() {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  uint keep_committed_regions = (uint)ceil((double)_stats->last_initial_mark_non_young_bytes() / HeapRegion::GrainBytes);
+  uint cur_non_young_regions = (uint)((double)_g1h->non_young_capacity_bytes() / HeapRegion::GrainBytes);
+
+  if (_setting->uncommit_ihop_set()) {
+    keep_committed_regions = (uint)ceil(((double)_g1h->capacity() * _setting->uncommit_ihop() / 100)
+                                         / HeapRegion::GrainBytes);
+  }
+
+  uint reserve_regions = 0;
+  if (keep_committed_regions > cur_non_young_regions) {
+    reserve_regions = keep_committed_regions - cur_non_young_regions;
+  }
+
+  // Keep some regions committed for old gen to grow
+  reserve_regions = MAX2(reserve_regions, (uint)ceil((double)_g1h->num_regions() * ElasticHeapOldGenReservePercent / 100));
+
+  // Free memory of regions in free list than non young part regardless of reserve regions in free list
+  _g1h->_hrm.prepare_old_region_list_to_free(_conc_thread->to_free_list(),
+        reserve_regions, _g1h->g1_policy()->calculate_young_list_desired_max_length());
+}
+
+uint ElasticHeap::calculate_young_list_desired_max_length() {
+  return _g1h->g1_policy()->calculate_young_list_desired_max_length();
+}
+
+double ElasticHeap::g1_reserve_factor() {
+  return _g1h->g1_policy()->_reserve_factor;
+}
+
+uint ElasticHeap::g1_reserve_regions() {
+  return _g1h->g1_policy()->_reserve_regions;
+}
+
+ElasticHeapEvaluator::ElasticHeapEvaluator(ElasticHeap* eh)
+  : _elas(eh) {
+  _g1h = _elas->_g1h;
+  _g1_policy = _g1h->g1_policy();
+  _hrm = &_g1h->_hrm;
+}
+
+void ElasticHeapEvaluator::sanity_check() {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  assert(_g1h->num_regions() == _g1h->max_regions(), "sanity");
+  assert(InitiatingHeapOccupancyPercent == _elas->_orig_ihop, "sanity");
+  assert(_elas->_orig_max_desired_young_length ==
+         _g1_policy->_young_gen_sizer->max_desired_young_length(), "sanity");
+  assert(_elas->_orig_min_desired_young_length ==
+         _g1_policy->_young_gen_sizer->min_desired_young_length(), "sanity");
+}
+
+void ElasticHeapEvaluator::evaluate_old_common() {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  if (ready_to_initial_mark()) {
+    _elas->check_to_initate_conc_mark();
+  }
+
+  if (!_elas->ready_to_uncommit_after_mixed_gc()) {
+    return;
+  }
+
+  _elas->uncommit_old_gen();
+}
+
+void RecoverEvaluator::evaluate() {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+  // Sanity check or recover any uncommitted regions
+  if (_hrm->num_uncommitted_regions() == 0) {
+    sanity_check();
+  } else {
+    _elas->commit_regions(_hrm->num_uncommitted_regions());
+  }
+}
+
+void PeriodicEvaluator::evaluate() {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  if (os::elapsedTime() < ElasticHeapPeriodicUncommitStartupDelay) {
+    return;
+  }
+
+  if (ElasticHeapPeriodicInitialMarkIntervalMillis != 0) {
+    evaluate_old();
+  }
+  evaluate_young();
+}
+
+void PeriodicEvaluator::evaluate_young() {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  // Do tuning until enough gc info collected
+  if (ElasticHeapPeriodicYGCIntervalMillis == 0 || _elas->stats()->num_normalized_interval() < GC_INTERVAL_SEQ_LENGTH) {
+    return;
+  }
+
+  // Now we caculate the lower bound and higher bound of young gc interval
+  uint low_interval = ElasticHeapPeriodicYGCIntervalMillis *
+                      (100 - ElasticHeapPeriodicYGCIntervalFloorPercent) / 100;
+  uint high_interval = ElasticHeapPeriodicYGCIntervalMillis *
+                       (100 + ElasticHeapPeriodicYGCIntervalCeilingPercent) / 100;
+
+  double last_normalized_interval = _elas->stats()->last_normalized_interval();
+  double avg_normalized_interval = _elas->stats()->avg_normalized_interval();
+
+  if (last_normalized_interval < high_interval && last_normalized_interval > low_interval) {
+    // last interval in proper range so do nothing
+    return;
+  }
+
+  // We have 3 conditions which will trigger young generation resize
+  // 1. last normalized interval less than ElasticHeapYGCIntervalMinMillis
+  // 2. average interval of last 10 gc is smaller than lower bound
+  // 3. average interval of last 10 gc is larger than higher bound
+  bool interval_too_small = last_normalized_interval < ElasticHeapYGCIntervalMinMillis;
+  bool avg_interval_larger_than_high = avg_normalized_interval > high_interval;
+  bool avg_interval_less_than_low = avg_normalized_interval < low_interval;
+
+  // Calcuate the minimal young list length according to ElasticHeapPeriodicMinYoungCommitPercent
+  uint min_young_list_length = _elas->max_young_length() *
+                               ElasticHeapPeriodicMinYoungCommitPercent / 100;
+
+  bool continue_resize = avg_interval_larger_than_high &&
+                         (_elas->calculate_young_list_desired_max_length()
+                           != min_young_list_length);
+
+  continue_resize |= (interval_too_small || avg_interval_less_than_low);
+
+  uint overlap_length = _elas->overlapped_young_regions_with_old_gen();
+  if (overlap_length > 0) {
+    continue_resize = true;
+  }
+
+  if (!continue_resize) {
+    return;
+  }
+
+  // Calcuate the target max young list length according to last gc interval
+  uint target_max_young_list_length = _elas->stats()->last_normalized_eden_consumed_length() *
+                                  ElasticHeapPeriodicYGCIntervalMillis / last_normalized_interval
+                                  + _g1h->young_list()->length() /* Survivor length after GC */;
+
+  if (overlap_length > 0) {
+    // Old region already overlapped young size, need more regions
+    target_max_young_list_length += overlap_length;
+    min_young_list_length += overlap_length;
+  }
+
+  // Minimal young list length should be larger than existent survivor
+  min_young_list_length = MAX2(min_young_list_length, _g1h->g1_policy()->recorded_survivor_regions() + 1);
+
+  // Constrain the target_max_young_list_length
+  target_max_young_list_length = MAX2(target_max_young_list_length, min_young_list_length);
+  target_max_young_list_length = MIN2(target_max_young_list_length, _elas->max_young_length());
+
+  _elas->resize_young_length(target_max_young_list_length);
+}
+
+bool PeriodicEvaluator::ready_to_initial_mark() {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  return ElasticHeapPeriodicInitialMarkIntervalMillis != 0 &&
+         ((os::elapsedTime() - _elas->stats()->last_initial_mark_timestamp_s()) >
+          (ElasticHeapPeriodicInitialMarkIntervalMillis / (double)MILLIUNITS));
+}
+
+void GenerationLimitEvaluator::evaluate() {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  evaluate_old();
+  evaluate_young();
+}
+
+void GenerationLimitEvaluator::evaluate_young() {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  // Calcuate the new target max length according to _young_percent
+  uint target_max_young_length;
+  if (_elas->setting()->young_percent() == 0) {
+    target_max_young_length = _elas->max_young_length();
+  } else {
+    target_max_young_length = _elas->max_young_length() * _elas->setting()->young_percent() / 100;
+  }
+
+  _elas->resize_young_length(target_max_young_length);
+}
+
+bool GenerationLimitEvaluator::ready_to_initial_mark() {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  if (_elas->setting()->uncommit_ihop() == 0) {
+    return false;
+  }
+  size_t threshold = _g1h->capacity()  * _elas->setting()->uncommit_ihop() / 100;
+
+  if (_g1h->non_young_capacity_bytes() > threshold) {
+    return true;
+  } else {
+    return false;
+  }
+}
+
+void SoftmxEvaluator::evaluate() {
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  assert(_elas->setting()->softmx_percent_set(), "Precondition");
+  uint target_heap_regions = (uint)ceil((double)_g1h->max_regions() * _elas->setting()->softmx_percent() / 100);
+  uint orig_uncommit_num = _g1h->max_regions() - _g1h->num_regions();
+  uint target_uncommit_num = _g1h->max_regions() - target_heap_regions;
+
+  if (target_uncommit_num == orig_uncommit_num) {
+    return;
+  } else if (target_uncommit_num < orig_uncommit_num) {
+    // Expand heap
+    uint regions_to_commit = orig_uncommit_num - target_uncommit_num;
+    _elas->commit_regions(regions_to_commit);
+  } else {
+    // Shrink heap
+    if (!_elas->stats()->check_mixed_gc_finished()) {
+      return;
+    }
+    uint regions_to_uncommit = target_uncommit_num - orig_uncommit_num;
+    int target_free_num = _hrm->num_free_regions() - regions_to_uncommit;
+
+    // Reserved regions for G1ReservePercent
+    int target_reserve_regions = (int)ceil((double)target_heap_regions * _elas->g1_reserve_factor());
+    // Reserved regions for young gen
+    target_reserve_regions += (int)ceil((double)target_heap_regions * G1NewSizePercent / 100);
+    // Reserved regions for old gen
+    target_reserve_regions += (int)ceil((double)target_heap_regions * ElasticHeapOldGenReservePercent / 100);
+
+    if (target_free_num < target_reserve_regions) {
+      // We don't have more free regions to uncommit
+      gclog_or_tty->print("(Elastic Heap softmx percent setting failed.)");
+      if (_hrm->num_uncommitted_regions() == 0) {
+        _elas->setting()->set_softmx_percent(0);
+      } else {
+        _elas->setting()->set_softmx_percent(_g1h->num_regions() * 100 / _g1h->max_regions());
+      }
+      return;
+    }
+
+    _elas->uncommit_regions(regions_to_uncommit);
+    _elas->change_heap_capacity(target_heap_regions);
+  }
+}

src/share/vm/gc_implementation/g1/elasticHeap.hpp

+/*
+ * Copyright (c) 2019 Alibaba Group Holding Limited. All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Alibaba designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef SHARE_VM_GC_IMPLEMENTATION_G1_ELASTICHEAP_HPP
+#define SHARE_VM_GC_IMPLEMENTATION_G1_ELASTICHEAP_HPP
+
+#include "gc_implementation/g1/heapRegionSet.hpp"
+#include "gc_implementation/g1/heapRegion.hpp"
+#include "runtime/mutex.hpp"
+#include "runtime/thread.inline.hpp"
+#include "utilities/exceptions.hpp"
+
+#define GC_INTERVAL_SEQ_LENGTH 10
+
+class ElasticHeap;
+
+// ElasticHeapConcThread:
+// Commit/uncommit memory (several GB) may cost significant time so we won't do it in STW.
+// We use a concurrent thread for doing commit/uncommit/pretouch the memory of regions
+// Heap regions will be removed from free list of _hrm and put into commit/uncommit list
+// for doing the commit/uncommit job and moved back into _hrm in next GC stw
+// after commit/uncommit finishes.
+
+class ElasticHeapConcThread : public NamedThread {
+friend class ElasticHeap;
+private:
+  ElasticHeap*        _elastic_heap;
+  // List of regions to uncommit
+  FreeRegionList      _uncommit_list;
+  // List of regions to commit
+  FreeRegionList      _commit_list;
+  // List of old regions to free
+  FreeRegionList      _to_free_list;
+
+  // Indicate the commit/uncommit is working
+  // Will be set when VM thread(GC) triggers ElasticHeapThread to do memory job
+  // and be cleared when the memory job finishes
+  //
+  // Java threads(Jcmd listener or MXBean) will check this flag if the memory work is done
+  // ElasticHeap::recover_for_full_gc will also check this flag
+  volatile bool       _working;
+
+  // ElasticHeapThread will wait on it for doing memory job
+  // And VM trhead(GC) will notify ElasticHeapThread to do memory job via _conc_lock
+  Monitor*            _conc_lock;
+  // Java threads(Jcmd listener or MXBean) will wait on _working_lock for the finish of memory work
+  // ElasticHeap::recover_for_full_gc will also wait on _working_lock for the finish of memory work
+  Monitor*            _working_lock;
+
+  // Number of parallel worker threads
+  uint                _parallel_worker_threads;
+  // Parallel workers
+  FlexibleWorkGang*   _parallel_workers;
+  // For terminating conc thread
+  bool                _should_terminate;
+  bool                _has_terminated;
+
+  void                sanity_check();
+  void                print_work_summary(uint uncommit_length, uint commit_length, double start);
+  // Commit/Uncommit phyical pages of regions
+  void                do_memory_job();
+  // Commit/Uncommit phyical pages of regions
+  uint                do_memory(FreeRegionList* list, HeapRegionClosure* cl);
+  // Parallel Commit/Uncommit phyical pages
+  void                par_work_on_regions(FreeRegionList* list, HeapRegionClosure* cl);
+  void                wait_for_universe_init();
+
+public:
+  ElasticHeapConcThread(ElasticHeap* elastic_heap);
+
+  // Region list for commit/uncommit
+  FreeRegionList*     uncommit_list()           { return &_uncommit_list; }
+  FreeRegionList*     commit_list()             { return &_commit_list; }
+  FreeRegionList*     to_free_list()            { return &_to_free_list; }
+
+  void                start();
+  bool                working() const           { return _working; }
+  void                set_working();
+  void                clear_working()           {
+    assert(_working, "Sanity");
+    _working = false;
+  }
+
+  // Lock for manipulating ElasticHeapThread data structures
+  Monitor*            conc_lock()               { return _conc_lock; }
+  Monitor*            working_lock()            { return _working_lock; }
+  void                sleep_before_next_cycle();
+  virtual void        run();
+  void                stop();
+
+  // Count of regions in FreeRegionList
+  uint                total_unavaiable_regions();
+};
+
+// Data structure for elastic heap timer thread
+// We will trigger young gc in this thread
+// but we cannot do it in a regular native thread(a limitation in JDK1.8)
+// so we have to make it a Java thread
+class ElasticHeapTimer : AllStatic {
+  friend class ElasticHeap;
+private:
+  volatile static bool _should_terminate;
+  static JavaThread*  _thread;
+  static Monitor*     _monitor;
+
+public:
+  // Timer thread entry
+  static void         timer_thread_entry(JavaThread* thread, TRAPS);
+  static void         start();
+  static void         stop();
+  static bool         has_error(TRAPS, const char* error);
+};
+
+class ElasticHeapEvaluator : public CHeapObj<mtGC> {
+protected:
+  ElasticHeap*        _elas;
+  G1CollectedHeap*    _g1h;
+  G1CollectorPolicy*  _g1_policy;
+  HeapRegionManager*  _hrm;
+public:
+  ElasticHeapEvaluator(ElasticHeap* eh);
+
+  void                sanity_check();
+  virtual void        evaluate() = 0;
+  virtual void        evaluate_young()                  { ShouldNotReachHere(); }
+  virtual void        evaluate_old()                    { ShouldNotReachHere(); }
+  virtual void        evaluate_old_common();
+
+  virtual bool        ready_to_initial_mark()       { ShouldNotReachHere(); }
+};
+
+class RecoverEvaluator : public ElasticHeapEvaluator {
+public:
+  RecoverEvaluator(ElasticHeap* eh)
+    : ElasticHeapEvaluator(eh) {}
+  virtual void        evaluate();
+};
+
+class PeriodicEvaluator : public ElasticHeapEvaluator {
+public:
+  PeriodicEvaluator(ElasticHeap* eh)
+    : ElasticHeapEvaluator(eh) {}
+  virtual void        evaluate();
+  virtual void        evaluate_young();
+  virtual void        evaluate_old()          { evaluate_old_common(); }
+  virtual bool        ready_to_initial_mark();
+};
+
+class GenerationLimitEvaluator : public ElasticHeapEvaluator {
+public:
+  GenerationLimitEvaluator(ElasticHeap* eh)
+    : ElasticHeapEvaluator(eh) {}
+  virtual void        evaluate();
+  virtual void        evaluate_young();
+  virtual void        evaluate_old()          { evaluate_old_common(); }
+  virtual bool        ready_to_initial_mark();
+};
+
+class SoftmxEvaluator : public ElasticHeapEvaluator {
+public:
+  SoftmxEvaluator(ElasticHeap* eh)
+    : ElasticHeapEvaluator(eh) {}
+  virtual void        evaluate();
+};
+
+class ElasticHeapGCStats : public CHeapObj<mtGC> {
+friend class ElasticHeap;
+public:
+  ElasticHeapGCStats(ElasticHeap*, G1CollectedHeap*);
+
+  double              avg_normalized_interval() const {
+    return _recent_ygc_normalized_interval_ms->avg();
+  }
+  double              last_normalized_interval() const {
+    return _recent_ygc_normalized_interval_ms->last();
+  }
+  int                 num_normalized_interval() const {
+    return _recent_ygc_normalized_interval_ms->num();
+  }
+  uint                last_normalized_eden_consumed_length() const {
+    return _last_normalized_eden_consumed_length;
+  }
+  double              last_initial_mark_timestamp_s() const {
+    return _last_initial_mark_timestamp_s;
+  }
+  double              last_initial_mark_interval_s() const {
+    return _last_initial_mark_interval_s;
+  }
+  size_t              last_initial_mark_non_young_bytes() const {
+    return _last_initial_mark_non_young_bytes;
+  }
+  // Reset the tracking info of mixed gc
+  void                reset_mixed_gc_info() {
+    _last_gc_mixed = false;
+    _mixed_gc_finished = false;;
+    _need_mixed_gc = false;
+  }
+
+  bool                last_gc_mixed() const          { return _last_gc_mixed; }
+
+  bool                need_mixed_gc() const          { return _need_mixed_gc; }
+  void                set_need_mixed_gc(bool f)      { _need_mixed_gc = f; }
+
+  double              last_gc_end_timestamp_s() const  { return _last_gc_end_timestamp_s; }
+  void                set_last_gc_end_timestamp_s(double s) { _last_gc_end_timestamp_s = s; }
+
+  void                track_gc_start(bool full_gc);
+
+  bool                check_mixed_gc_finished();
+private:
+  ElasticHeap*        _elas;
+  G1CollectedHeap*    _g1h;
+  // G1 will use non-fixed size of young generation
+  // We scale the gc interval to a normalized interval as max size of young generation
+  // e.g. we make interval X 2 if last GC only used 1/2 of max size of young gen
+  TruncatedSeq*       _recent_ygc_normalized_interval_ms;
+  // Time of last GC in seccond
+  volatile double     _last_gc_end_timestamp_s;
+  // Time of initial mark in seccond
+  volatile double     _last_initial_mark_timestamp_s;
+  // If last gc is mixed gc
+  volatile bool       _last_gc_mixed;
+  // If mixed gc has finished
+  volatile bool       _mixed_gc_finished;
+  // If mixed gc needs to happen
+  volatile bool       _need_mixed_gc;
+  // The interval in second between last 2 intial-marks
+  volatile double     _last_initial_mark_interval_s;
+  // Bytes of non-young part in last initial mark
+  size_t              _last_initial_mark_non_young_bytes;
+  // Number of eden regions consumed in last gc interval(normalized)
+  uint                _last_normalized_eden_consumed_length;
+};
+
+class ElasticHeapSetting;
+
+// ElasticHeap:
+// Main class of elastic heap feature
+class ElasticHeap : public CHeapObj<mtGC> {
+friend class ElasticHeapEvaluator;
+friend class RecoverEvaluator;
+friend class PeriodicEvaluator;
+friend class GenerationLimitEvaluator;
+friend class SoftmxEvaluator;
+public:
+  ElasticHeap(G1CollectedHeap* g1h);
+  ~ElasticHeap();
+
+  enum ErrorType {
+    NoError = 0,
+    HeapAdjustInProgress,
+    GCTooFrequent,
+    IllegalYoungPercent,
+    IllegalMode
+  };
+
+  // Modes when elastic heap is activated
+  enum EvaluationMode {
+    InactiveMode = 0,
+    PeriodicUncommitMode,
+    GenerationLimitMode,
+    SoftmxMode,
+    EvaluationModeNum
+  };
+
+  static uint         ignore_arg();
+
+  ElasticHeapGCStats* stats()         { return _stats; }
+  ElasticHeapSetting* setting()       { return _setting; }
+private:
+  G1CollectedHeap*    _g1h;
+  ElasticHeapGCStats* _stats;
+  ElasticHeapSetting* _setting;
+  // Initial value of InitiatingHeapOccupancyPercent
+  uint                _orig_ihop;
+  // Initial value of desired young length
+  uint                _orig_min_desired_young_length;
+  uint                _orig_max_desired_young_length;
+
+  // Indicates in the concurrent working cycle of memory job
+  // 1. A concurrent cycle starts (start_conc_cycle) in VM Thread(GC stw) when triggering
+  // ElasticHeapConcThread to do memory job
+  // 2. A concurrent cycle ends (end_conc_cycle) in the next gc pause after region
+  // commit/uncommit finishes and move regions in ElasticHeapConcThread back into _hrm
+  volatile bool       _in_conc_cycle;
+
+  // Concurrent thread for doing memory job
+  ElasticHeapConcThread*  _conc_thread;
+
+  volatile int        _configure_setting_lock;
+
+  ElasticHeapEvaluator* _evaluators[EvaluationModeNum];
+
+  bool _heap_capacity_changed;
+
+  void                start_conc_cycle();
+  void                end_conc_cycle();
+
+  void                move_regions_back_to_hrm();
+  // Move the regions in _thread back to _hrm and clear in_cycle
+  void                finish_conc_cycle();
+  // Check completion of previous ElasticHeapConcThread work
+  void                check_end_of_previous_conc_cycle();
+  // Update heap size information after expanding completes
+  void                update_expanded_heap_size();
+  // Do the elastic heap evaluation and operation
+  void                evaluate_elastic_work();
+
+  void                try_starting_conc_cycle();
+
+  void                wait_for_conc_thread_working_done(bool safepointCheck);
+  bool                enough_free_regions_to_uncommit(uint num_regions_to_uncommit);
+
+  // Update min/max desired young length after change young length
+  void                update_desired_young_length(uint unavailable_young_length);
+
+public:
+  void                uncommit_region_memory(HeapRegion* hr);
+  void                commit_region_memory(HeapRegion* hr, bool pretouch);
+  void                free_region_memory(HeapRegion* hr);
+
+  bool                in_conc_cycle()              { return _in_conc_cycle; }
+
+  // Record gc information
+  void                record_gc_start(bool full_gc = false);
+  void                record_gc_end();
+
+  void                prepare_in_gc_start();
+
+  // Main entry in GC pause for elastic heap
+  void                perform();
+  // Commit/uncommit regions
+  void                uncommit_regions(uint num);
+  void                commit_regions(uint num);
+
+  void                resize_young_length(uint target_length);
+  void                change_heap_capacity(uint target_heap_regions);
+  void                change_young_size_for_softmx();
+
+  uint                max_young_length() const      { return _orig_max_desired_young_length; }
+
+  // Number of regions that old gen overlap with young gen
+  // So young gen cannot use as many as MaxNewSize
+  uint                overlapped_young_regions_with_old_gen();
+
+  uint                num_unavailable_regions();
+
+  // Main entry for processing elastic heap via JCMD/MXBean
+  ErrorType           configure_setting(uint young_percent, uint uncommit_ihop, uint softmx_percent);
+
+  // Get the commit percent and freed bytes
+  int                 young_commit_percent() const;
+  jlong               young_uncommitted_bytes() const;
+  int                 softmx_percent() const;
+  jlong               uncommitted_bytes() const;
+  int                 uncommit_ihop() const;
+
+  // Wait for the conc thread working done and finish the current cycle
+  void                wait_for_conc_cycle_end();
+  // If Full GC happens in auto mode, elastic heap will wait to recover the uncommitted regions
+  void                wait_to_recover();
+
+  // If the gc is triggered by elastic heap to resize young gen
+  bool                is_gc_to_resize_young_gen();
+  // Max survivor regions in this gc.
+  // We probably do a young gen resize in the end of gc
+  // so we cannot leave a too large survior size if we will make young gen smaller
+  uint                max_available_survivor_regions();
+
+  // Check to initiate initial-mark
+  void                check_to_initate_conc_mark();
+  // Check to invoke a GC
+  void                check_to_trigger_ygc();
+
+  // With softmx mode, we will change the capacity of heap
+  bool                heap_capacity_changed()     { return _heap_capacity_changed; }
+  void                set_heap_capacity_changed(uint num);
+
+  EvaluationMode      evaluation_mode() const;
+  bool                conflict_mode(EvaluationMode target_mode);
+
+  // Get string from error type
+  static const char*  to_string(ErrorType type) {
+    switch(type) {
+      case HeapAdjustInProgress: return "last elastic-heap resize is still in progress";
+      case GCTooFrequent: return "gc is too frequent";
+      case IllegalYoungPercent: return "illegal percent";
+      case IllegalMode: return "not in correct mode";
+      default: ShouldNotReachHere(); return NULL;
+    }
+  }
+
+  // Get string from EvaluationMode
+  static const char*  to_string(EvaluationMode mode) {
+    switch (mode) {
+      case InactiveMode: return "inactive";
+      case PeriodicUncommitMode: return "periodic uncommit";
+      case GenerationLimitMode: return "generation limit";
+      case SoftmxMode: return "softmx";
+      default: ShouldNotReachHere(); return NULL;
+    }
+  }
+
+  void                destroy();
+
+  bool                can_turn_on_periodic_uncommit();
+
+  bool                ready_to_uncommit_after_mixed_gc();
+  void                uncommit_old_gen();
+
+
+  uint                calculate_young_list_desired_max_length();
+  double              g1_reserve_factor();
+  uint                g1_reserve_regions();
+};
+
+class ElasticHeapSetting : public CHeapObj<mtGC> {
+friend class ElasticHeap;
+public:
+  ElasticHeapSetting(ElasticHeap*, G1CollectedHeap*);
+  // Whether do elastic heap resize by explicit command
+  bool                generation_limit_set() const {
+      return young_percent_set() || uncommit_ihop_set();
+  }
+  // Whether a jcmd/mxbean command set the young commit percent
+  bool                young_percent_set() const {
+    return _young_percent != 0;
+  }
+  uint                young_percent() const {
+    return _young_percent;
+  }
+  uint                set_young_percent(uint p) {
+    _young_percent = p;
+  }
+  // Whether a jcmd/mxbean command set the uncommit ihop
+  bool                uncommit_ihop_set() const {
+    return _uncommit_ihop != 0;
+  }
+  uint                uncommit_ihop() const {
+    return _uncommit_ihop;
+  }
+  bool                softmx_percent_set() const {
+    return _softmx_percent != 0;
+  }
+  uint                softmx_percent() const {
+    return _softmx_percent;
+  }
+  void                set_softmx_percent(uint p) {
+    _softmx_percent = p;
+  }
+
+  ElasticHeap::ErrorType change_young_percent(uint young_percent, bool& trigger_gc);
+  ElasticHeap::ErrorType change_uncommit_ihop(uint uncommit_ihop, bool& trigger_gc);
+  ElasticHeap::ErrorType change_softmx_percent(uint softmx_percent, bool& trigger_gc);
+  ElasticHeap::ErrorType process_arg(uint young_percent, uint uncommit_ihop, uint softmx_percent,
+                                     bool& trigger_gc);
+  ElasticHeap::EvaluationMode target_evaluation_mode(uint young_percent,
+                                             uint uncommit_ihop,
+                                             uint softmx_percent);
+private:
+  ElasticHeap*        _elas;
+  G1CollectedHeap*    _g1h;
+  // Young list percentage set by command
+  volatile uint       _young_percent;
+  // Set the initiating heap occupancy for elastic heap and do uncommit after concurrent gc
+  volatile uint       _uncommit_ihop;
+  // Set the softmx percent
+  volatile uint       _softmx_percent;
+
+  // Check if we can change the young percent by jcmd/MXBean
+  bool                can_change_young_percent(uint percent);
+
+  static uint         ignore_arg()  { return (uint)-1; }
+  static bool         ignore_arg(uint arg, uint cur_value)  {
+    return arg == cur_value || arg == ignore_arg();
+  }
+};
+
+#endif // SHARE_VM_GC_IMPLEMENTATION_G1_ELASTICHEAP_HPP

src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp

@@ -67,6 +67,7 @@
 #include "oops/oop.pcgc.inline.hpp"
 #include "runtime/orderAccess.inline.hpp"
 #include "runtime/vmThread.hpp"
+#include "gc_implementation/g1/elasticHeap.hpp"
 
 size_t G1CollectedHeap::_humongous_object_threshold_in_words = 0;
 
@@ -775,7 +776,8 @@ HeapWord* G1CollectedHeap::humongous_obj_allocate(size_t word_size, AllocationCo
     }
   }
 
-  if (first == G1_NO_HRM_INDEX) {
+  // With G1ElasticHeap we don't allocate from (elastic) unavailable regions
+  if (first == G1_NO_HRM_INDEX && !G1ElasticHeap) {
     // Policy: We could not find enough regions for the humongous object in the
     // free list. Look through the heap to find a mix of free and uncommitted regions.
     // If so, try expansion.
@@ -1296,6 +1298,21 @@ bool G1CollectedHeap::do_collection(bool explicit_gc,
       double start = os::elapsedTime();
       g1_policy()->record_full_collection_start();
 
+      // With ElasticHeap, we may wait to finish some work
+      if (G1ElasticHeap) {
+        elastic_heap()->record_gc_start(true);
+        if (explicit_gc) {
+          // In explicit full gc, wait for conc cycle to finish
+          elastic_heap()->wait_for_conc_cycle_end();
+        } else {
+         if (ElasticHeapPeriodicUncommit) {
+          // If not explicit full gc and in elastic heap periodic GC mode
+          // recover the uncommitted regions
+          elastic_heap()->wait_to_recover();
+         }
+        }
+      }
+
       // Note: When we have a more flexible GC logging framework that
       // allows us to add optional attributes to a GC log record we
       // could consider timing and reporting how long we wait in the
@@ -1538,6 +1555,10 @@ bool G1CollectedHeap::do_collection(bool explicit_gc,
 
     post_full_gc_dump(gc_timer);
 
+    if (G1ElasticHeap) {
+      elastic_heap()->record_gc_end();
+    }
+
     gc_timer->register_gc_end();
     gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
   }
@@ -1560,6 +1581,10 @@ void G1CollectedHeap::do_full_collection(bool clear_all_soft_refs) {
 void
 G1CollectedHeap::
 resize_if_necessary_after_full_collection(size_t word_size) {
+  if (G1ElasticHeap) {
+    // We never resize heap in full GC with elastic heap
+    return;
+  }
   // Include the current allocation, if any, and bytes that will be
   // pre-allocated to support collections, as "used".
   const size_t used_after_gc = used();
@@ -1762,6 +1787,11 @@ bool G1CollectedHeap::expand(size_t expand_bytes) {
     return false;
   }
 
+  if (G1ElasticHeap && G1CollectedHeap::heap()->elastic_heap() != NULL) {
+    // Heap initialization completes. Don't expand ever.
+    return false;
+  }
+
   uint regions_to_expand = (uint)(aligned_expand_bytes / HeapRegion::GrainBytes);
   assert(regions_to_expand > 0, "Must expand by at least one region");
 
@@ -1860,6 +1890,7 @@ G1CollectedHeap::G1CollectedHeap(G1CollectorPolicy* policy_) :
   _has_humongous_reclaim_candidates(false),
   _free_regions_coming(false),
   _young_list(new YoungList(this)),
+  _elastic_heap(NULL),
   _gc_time_stamp(0),
   _survivor_plab_stats(YoungPLABSize, PLABWeight),
   _old_plab_stats(OldPLABSize, PLABWeight),
@@ -1952,6 +1983,19 @@ jint G1CollectedHeap::initialize() {
   size_t max_byte_size = collector_policy()->max_heap_byte_size();
   size_t heap_alignment = collector_policy()->heap_alignment();
 
+  if (G1ElasticHeap) {
+    size_t page_size = UseLargePages ? os::large_page_size() : os::vm_page_size();
+    if (HeapRegion::GrainBytes < page_size || (HeapRegion::GrainBytes % page_size) != 0) {
+      vm_exit_during_initialization(err_msg("G1ElasticHeap requires G1HeapRegionSize("
+                                            SIZE_FORMAT
+                                            " bytes) is multiple times of OS page size("
+                                            SIZE_FORMAT
+                                            " bytes)",
+                                             HeapRegion::GrainBytes, page_size));
+      return JNI_EINVAL;
+    }
+  }
+
   // Ensure that the sizes are properly aligned.
   Universe::check_alignment(init_byte_size, HeapRegion::GrainBytes, "g1 heap");
   Universe::check_alignment(max_byte_size, HeapRegion::GrainBytes, "g1 heap");
@@ -2081,6 +2125,10 @@ jint G1CollectedHeap::initialize() {
   // Perform any initialization actions delegated to the policy.
   g1_policy()->init();
 
+  if (G1ElasticHeap) {
+    _elastic_heap = new ElasticHeap(this);
+  }
+
   JavaThread::satb_mark_queue_set().initialize(SATB_Q_CBL_mon,
                                                SATB_Q_FL_lock,
                                                G1SATBProcessCompletedThreshold,
@@ -2145,6 +2193,9 @@ void G1CollectedHeap::stop() {
   // that are destroyed during shutdown.
   _cg1r->stop();
   _cmThread->stop();
+  if (G1ElasticHeap) {
+    elastic_heap()->destroy();
+  }
   if (G1StringDedup::is_enabled()) {
     G1StringDedup::stop();
   }
@@ -2522,6 +2573,7 @@ void G1CollectedHeap::collect(GCCause::Cause cause) {
       }
     } else {
       if (cause == GCCause::_gc_locker || cause == GCCause::_wb_young_gc
+          || cause == GCCause::_g1_elastic_heap_trigger_gc
           DEBUG_ONLY(|| cause == GCCause::_scavenge_alot)) {
 
         // Schedule a standard evacuation pause. We're setting word_size
@@ -4033,6 +4085,10 @@ G1CollectedHeap::do_collection_pause_at_safepoint(double target_pause_time_ms) {
     { // Call to jvmpi::post_class_unload_events must occur outside of active GC
       IsGCActiveMark x;
 
+      if (G1ElasticHeap) {
+        elastic_heap()->prepare_in_gc_start();
+      }
+
       gc_prologue(false);
       increment_total_collections(false /* full gc */);
       increment_gc_time_stamp();
@@ -4244,6 +4300,10 @@ G1CollectedHeap::do_collection_pause_at_safepoint(double target_pause_time_ms) {
         _cm->verify_no_cset_oops();
         _cm->note_end_of_gc();
 
+        if (G1ElasticHeap) {
+          elastic_heap()->perform();
+        }
+
         // This timing is only used by the ergonomics to handle our pause target.
         // It is unclear why this should not include the full pause. We will
         // investigate this in CR 7178365.

src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp

@@ -44,6 +44,7 @@
 #include "memory/memRegion.hpp"
 #include "memory/sharedHeap.hpp"
 #include "utilities/stack.hpp"
+#include "gc_implementation/g1/elasticHeap.hpp"
 
 // A "G1CollectedHeap" is an implementation of a java heap for HotSpot.
 // It uses the "Garbage First" heap organization and algorithm, which
@@ -75,6 +76,7 @@ class G1NewTracer;
 class G1OldTracer;
 class EvacuationFailedInfo;
 class nmethod;
+class ElasticHeap;
 
 typedef OverflowTaskQueue<StarTask, mtGC>         RefToScanQueue;
 typedef GenericTaskQueueSet<RefToScanQueue, mtGC> RefToScanQueueSet;
@@ -184,6 +186,8 @@ class G1CollectedHeap : public SharedHeap {
   friend class MutatorAllocRegion;
   friend class SurvivorGCAllocRegion;
   friend class OldGCAllocRegion;
+  friend class ElasticHeap;
+  friend class ElasticHeapEvaluator;
   friend class G1Allocator;
   friend class G1DefaultAllocator;
   friend class G1ResManAllocator;
@@ -447,6 +451,8 @@ protected:
   // The young region list.
   YoungList*  _young_list;
 
+  ElasticHeap* _elastic_heap;
+
   // The current policy object for the collector.
   G1CollectorPolicy* _g1_policy;
 
@@ -1101,7 +1107,13 @@ public:
   }
 
   // The current number of regions in the heap.
-  uint num_regions() const { return _hrm.length(); }
+  uint num_regions() const {
+    if (G1ElasticHeap && elastic_heap() != NULL && !elastic_heap()->heap_capacity_changed()) {
+      return _hrm.max_length();
+    } else {
+      return _hrm.length();
+    }
+  }
 
   // The max number of regions in the heap.
   uint max_regions() const { return _hrm.max_length(); }
@@ -1482,6 +1494,8 @@ public:
 
   YoungList* young_list() const { return _young_list; }
 
+  ElasticHeap* elastic_heap() const { return _elastic_heap; }
+
   // debugging
   bool check_young_list_well_formed() {
     return _young_list->check_list_well_formed();

src/share/vm/gc_implementation/g1/g1CollectorPolicy.cpp

@@ -41,6 +41,7 @@
 #include "runtime/java.hpp"
 #include "runtime/mutexLocker.hpp"
 #include "utilities/debug.hpp"
+#include "gc_implementation/g1/elasticHeap.hpp"
 
 // Different defaults for different number of GC threads
 // They were chosen by running GCOld and SPECjbb on debris with different
@@ -1483,6 +1484,12 @@ void G1CollectorPolicy::update_survivors_policy() {
   // smaller than 1.0) we'll get 1.
   _max_survivor_regions = (uint) ceil(max_survivor_regions_d);
 
+  if (G1ElasticHeap && _g1->elastic_heap()->is_gc_to_resize_young_gen()) {
+    // If elastic heap will shrink the young gen
+    // we need to make the survivor less than the target young gen size
+    _max_survivor_regions = MIN2(_max_survivor_regions, _g1->elastic_heap()->max_available_survivor_regions());
+  }
+
   _tenuring_threshold = _survivors_age_table.compute_tenuring_threshold(
         HeapRegion::GrainWords * _max_survivor_regions);
 }

src/share/vm/gc_implementation/g1/g1CollectorPolicy.hpp

@@ -39,6 +39,7 @@
 class HeapRegion;
 class CollectionSetChooser;
 class G1GCPhaseTimes;
+class ElasticHeap;
 
 // TraceGen0Time collects data on _both_ young and mixed evacuation pauses
 // (the latter may contain non-young regions - i.e. regions that are
@@ -158,9 +159,17 @@ public:
   bool adaptive_young_list_length() {
     return _adaptive_size;
   }
+  void resize_min_desired_young_length(uint size) {
+    _min_desired_young_length = size;
+  }
+  void resize_max_desired_young_length(uint size) {
+    _max_desired_young_length = size;
+  }
 };
 
 class G1CollectorPolicy: public CollectorPolicy {
+  friend class ElasticHeap;
+  friend class ElasticHeapEvaluator;
 private:
   static G1IHOPControl* create_ihop_control();
 
@@ -843,6 +852,10 @@ public:
     _gcs_are_young = gcs_are_young;
   }
 
+  bool last_young_gc() const {
+    return _last_young_gc;
+  }
+
   bool adaptive_young_list_length() {
     return _young_gen_sizer->adaptive_young_list_length();
   }

src/share/vm/gc_implementation/g1/g1PageBasedVirtualSpace.cpp

@@ -224,6 +224,21 @@ bool G1PageBasedVirtualSpace::commit(size_t start_page, size_t size_in_pages) {
   return zero_filled;
 }
 
+void G1PageBasedVirtualSpace::par_commit(size_t start_page, size_t size_in_pages, bool allow_pretouch) {
+  // We need to make sure to commit all pages covered by the given area.
+  guarantee(is_area_uncommitted(start_page, size_in_pages), "Specified area is not uncommitted");
+  guarantee(!_special, "sanity");
+
+  size_t end_page = start_page + size_in_pages;
+
+  commit_internal(start_page, end_page);
+  _committed.par_set_range(start_page, end_page, BitMap::unknown_range);
+
+  if (AlwaysPreTouch && allow_pretouch) {
+    pretouch_internal(start_page, end_page);
+  }
+}
+
 void G1PageBasedVirtualSpace::uncommit_internal(size_t start_page, size_t end_page) {
   guarantee(start_page < end_page,
             err_msg("Given start page " SIZE_FORMAT " is larger or equal to end page " SIZE_FORMAT, start_page, end_page));
@@ -232,6 +247,14 @@ void G1PageBasedVirtualSpace::uncommit_internal(size_t start_page, size_t end_pa
   os::uncommit_memory(start_addr, pointer_delta(bounded_end_addr(end_page), start_addr, sizeof(char)));
 }
 
+void G1PageBasedVirtualSpace::free_memory_internal(size_t start_page, size_t end_page) {
+  guarantee(start_page < end_page,
+            err_msg("Given start page " SIZE_FORMAT " is larger or equal to end page " SIZE_FORMAT, start_page, end_page));
+
+  char* start_addr = page_start(start_page);
+  os::free_memory(start_addr, pointer_delta(bounded_end_addr(end_page), start_addr, sizeof(char)), _page_size);
+}
+
 void G1PageBasedVirtualSpace::uncommit(size_t start_page, size_t size_in_pages) {
   guarantee(is_area_committed(start_page, size_in_pages), "checking");
 
@@ -247,6 +270,23 @@ void G1PageBasedVirtualSpace::uncommit(size_t start_page, size_t size_in_pages)
   _committed.clear_range(start_page, end_page);
 }
 
+void G1PageBasedVirtualSpace::par_uncommit(size_t start_page, size_t size_in_pages) {
+  guarantee(is_area_committed(start_page, size_in_pages), "checking");
+  guarantee(!_special, "sanity");
+
+  size_t end_page = start_page + size_in_pages;
+  uncommit_internal(start_page, end_page);
+  _committed.par_clear_range(start_page, end_page, BitMap::unknown_range);
+}
+
+void G1PageBasedVirtualSpace::free_memory(size_t start_page, size_t size_in_pages) {
+  guarantee(is_area_committed(start_page, size_in_pages), "checking");
+  guarantee(!_special, "sanity");
+
+  size_t end_page = start_page + size_in_pages;
+  free_memory_internal(start_page, end_page);
+}
+
 bool G1PageBasedVirtualSpace::contains(const void* p) const {
   return _low_boundary <= (const char*) p && (const char*) p < _high_boundary;
 }

src/share/vm/gc_implementation/g1/g1PageBasedVirtualSpace.hpp

@@ -85,6 +85,9 @@ class G1PageBasedVirtualSpace VALUE_OBJ_CLASS_SPEC {
   // Uncommit the given memory range.
   void uncommit_internal(size_t start_page, size_t end_page);
 
+  // Free the given memory range.
+  void free_memory_internal(size_t start_page, size_t end_page);
+
   // Pretouch the given memory range.
   void pretouch_internal(size_t start_page, size_t end_page);
 
@@ -117,6 +120,15 @@ class G1PageBasedVirtualSpace VALUE_OBJ_CLASS_SPEC {
   // Uncommit the given area of pages starting at start being size_in_pages large.
   void uncommit(size_t start_page, size_t size_in_pages);
 
+  // MT-safe commit the given area of pages starting at start being size_in_pages large.
+  void par_commit(size_t start_page, size_t size_in_pages, bool allow_pretouch = true);
+
+  // MT-safe uncommit the given area of pages starting at start being size_in_pages large.
+  void par_uncommit(size_t start_page, size_t size_in_pages);
+
+  // Free the given area of pages starting at start being size_in_pages large.
+  void free_memory(size_t start_page, size_t size_in_pages);
+
   // Initialize the given reserved space with the given base address and the size
   // actually used.
   // Prefer to commit in page_size chunks.

src/share/vm/gc_implementation/g1/g1RegionToSpaceMapper.cpp

@@ -76,6 +76,21 @@ class G1RegionsLargerThanCommitSizeMapper : public G1RegionToSpaceMapper {
     _storage.uncommit((size_t)start_idx * _pages_per_region, num_regions * _pages_per_region);
     _commit_map.clear_range(start_idx, start_idx + num_regions);
   }
+
+  virtual void par_commit_region_memory(uint idx) {
+    _storage.par_commit((size_t)idx * _pages_per_region, _pages_per_region, false);
+    _commit_map.par_set_range(idx, idx + 1, BitMap::unknown_range);
+  }
+
+  virtual void par_uncommit_region_memory(uint idx) {
+    _storage.par_uncommit((size_t)idx * _pages_per_region, _pages_per_region);
+    _commit_map.par_clear_range(idx, idx + 1, BitMap::unknown_range);
+  }
+
+  virtual void free_region_memory(uint idx) {
+    _storage.free_memory((size_t)idx * _pages_per_region, _pages_per_region);
+  }
+
 };
 
 // G1RegionToSpaceMapper implementation where the region granularity is smaller
@@ -139,6 +154,18 @@ class G1RegionsSmallerThanCommitSizeMapper : public G1RegionToSpaceMapper {
       _commit_map.clear_bit(i);
     }
   }
+
+  virtual void par_commit_region_memory(uint idx) {
+    ShouldNotReachHere();
+  }
+
+  virtual void par_uncommit_region_memory(uint idx) {
+    ShouldNotReachHere();
+  }
+
+  virtual void free_region_memory(uint idx) {
+    ShouldNotReachHere();
+  }
 };
 
 void G1RegionToSpaceMapper::fire_on_commit(uint start_idx, size_t num_regions, bool zero_filled) {

src/share/vm/gc_implementation/g1/g1RegionToSpaceMapper.hpp

@@ -72,6 +72,9 @@ class G1RegionToSpaceMapper : public CHeapObj<mtGC> {
 
   virtual void commit_regions(uint start_idx, size_t num_regions = 1) = 0;
   virtual void uncommit_regions(uint start_idx, size_t num_regions = 1) = 0;
+  virtual void par_commit_region_memory(uint idx) = 0;
+  virtual void par_uncommit_region_memory(uint idx) = 0;
+  virtual void free_region_memory(uint idx) = 0;
 
   // Creates an appropriate G1RegionToSpaceMapper for the given parameters.
   // The actual space to be used within the given reservation is given by actual_size.

src/share/vm/gc_implementation/g1/heapRegionManager.cpp

@@ -29,6 +29,8 @@
 #include "gc_implementation/g1/g1CollectedHeap.inline.hpp"
 #include "gc_implementation/g1/concurrentG1Refine.hpp"
 #include "memory/allocation.hpp"
+#include "runtime/os.hpp"
+#include "gc_implementation/g1/elasticHeap.hpp"
 
 void HeapRegionManager::initialize(G1RegionToSpaceMapper* heap_storage,
                                G1RegionToSpaceMapper* prev_bitmap,
@@ -91,6 +93,33 @@ void HeapRegionManager::commit_regions(uint index, size_t num_regions) {
   _card_counts_mapper->commit_regions(index, num_regions);
 }
 
+void HeapRegionManager::uncommit_region_memory(uint idx) {
+  assert(G1ElasticHeap, "Precondition");
+  // Print before uncommitting.
+  if (G1CollectedHeap::heap()->hr_printer()->is_active()) {
+    HeapRegion* hr = at(idx);
+    G1CollectedHeap::heap()->hr_printer()->uncommit(hr->bottom(), hr->end());
+  }
+
+  _heap_mapper->par_uncommit_region_memory(idx);
+}
+
+void HeapRegionManager::commit_region_memory(uint idx) {
+  assert(G1ElasticHeap, "Precondition");
+  // Print before committing.
+  if (G1CollectedHeap::heap()->hr_printer()->is_active()) {
+    HeapRegion* hr = at(idx);
+    G1CollectedHeap::heap()->hr_printer()->commit(hr->bottom(), hr->end());
+  }
+
+  _heap_mapper->par_commit_region_memory(idx);
+}
+
+void HeapRegionManager::free_region_memory(uint idx) {
+  assert(G1ElasticHeap, "Precondition");
+  _heap_mapper->free_region_memory(idx);
+}
+
 void HeapRegionManager::uncommit_regions(uint start, size_t num_regions) {
   guarantee(num_regions >= 1, err_msg("Need to specify at least one region to uncommit, tried to uncommit zero regions at %u", start));
   guarantee(_num_committed >= num_regions, "pre-condition");
@@ -172,6 +201,11 @@ uint HeapRegionManager::expand_at(uint start, uint num_regions) {
     return 0;
   }
 
+  if (G1ElasticHeap && G1CollectedHeap::heap()->elastic_heap() != NULL) {
+    // Heap initialization completes. Don't expand ever.
+    return 0;
+  }
+
   uint cur = start;
   uint idx_last_found = 0;
   uint num_last_found = 0;
@@ -197,7 +231,7 @@ uint HeapRegionManager::find_contiguous(size_t num, bool empty_only) {
 
   while (length_found < num && cur < max_length()) {
     HeapRegion* hr = _regions.get_by_index(cur);
-    if ((!empty_only && !is_available(cur)) || (is_available(cur) && hr != NULL && hr->is_empty())) {
+    if ((!empty_only && !is_available(cur) && !G1ElasticHeap) || (is_available(cur) && hr != NULL && hr->is_empty())) {
       // This region is a potential candidate for allocation into.
       length_found++;
     } else {
@@ -353,6 +387,135 @@ void HeapRegionManager::par_iterate(HeapRegionClosure* blk, uint worker_id, uint
   }
 }
 
+void HeapRegionManager::commit_region_memory(FreeRegionList* list) {
+  assert(G1ElasticHeap, "Precondition");
+
+  FreeRegionListIterator iter(list);
+  while (iter.more_available()) {
+    HeapRegion* hr = iter.get_next();
+    commit_region_memory(hr->hrm_index());
+  }
+}
+
+void HeapRegionManager::uncommit_region_memory(FreeRegionList* list) {
+  assert(G1ElasticHeap, "Precondition");
+
+  FreeRegionListIterator iter(list);
+  while (iter.more_available()) {
+    HeapRegion* hr = iter.get_next();
+    uncommit_region_memory(hr->hrm_index());
+  }
+}
+
+void HeapRegionManager::set_region_available(FreeRegionList* list) {
+  assert(G1ElasticHeap, "Precondition");
+  FreeRegionListIterator iter(list);
+  while (iter.more_available()) {
+    HeapRegion* hr = iter.get_next();
+    _available_map.par_set_range(hr->hrm_index(), hr->hrm_index() + 1, BitMap::unknown_range);
+  }
+  _num_committed += list->length();
+}
+
+void HeapRegionManager::set_region_unavailable(FreeRegionList* list) {
+  assert(G1ElasticHeap, "Precondition");
+  FreeRegionListIterator iter(list);
+  while (iter.more_available()) {
+    HeapRegion* hr = iter.get_next();
+    _available_map.par_clear_range(hr->hrm_index(), hr->hrm_index() + 1, BitMap::unknown_range);
+  }
+  assert(_num_committed > list->length(), "sanity");
+  _num_committed -= list->length();
+}
+
+uint HeapRegionManager::num_uncommitted_regions() {
+  assert(G1ElasticHeap, "Precondition");
+  return _uncommitted_list.length();
+}
+
+void HeapRegionManager::recover_uncommitted_regions() {
+  assert(G1ElasticHeap, "Precondition");
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  commit_region_memory(&_uncommitted_list);
+  set_region_available(&_uncommitted_list);
+  _free_list.add_ordered(&_uncommitted_list);
+}
+
+void HeapRegionManager::move_to_uncommitted_list(FreeRegionList* list) {
+  assert(G1ElasticHeap, "Precondition");
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  _uncommitted_list.add_ordered(list);
+}
+
+void HeapRegionManager::move_to_free_list(FreeRegionList* list) {
+  assert(G1ElasticHeap, "Precondition");
+  assert_at_safepoint(true /* should_be_vm_thread */);
+
+  set_region_available(list);
+  _free_list.add_ordered(list);
+}
+
+void HeapRegionManager::prepare_uncommit_regions(FreeRegionList* list, uint num) {
+  assert(G1ElasticHeap, "Precondition");
+  assert(num <= _free_list.length(), "sanity");
+  assert_at_safepoint(true /* should_be_vm_thread */);
+  assert(list->is_empty(), "sanity");
+
+  G1CollectedHeap* g1h = G1CollectedHeap::heap();
+  for (uint i = 0; i < num; i++) {
+    HeapRegion* hr = _free_list.remove_region(false /* from_head */);
+    list->add_ordered(hr);
+  }
+  set_region_unavailable(list);
+}
+
+void HeapRegionManager::prepare_commit_regions(FreeRegionList* list, uint num) {
+  assert(G1ElasticHeap, "Precondition");
+  assert(num <= _uncommitted_list.length(), "sanity");
+  assert_at_safepoint(true /* should_be_vm_thread */);
+  assert(list->is_empty(), "sanity");
+
+  G1CollectedHeap* g1h = G1CollectedHeap::heap();
+  for (uint i = 0; i < num; i++) {
+    HeapRegion* hr = _uncommitted_list.remove_region(true /* from_head */);
+    assert(!is_available(hr->hrm_index()), "sanity");
+    list->add_ordered(hr);
+  }
+}
+
+void HeapRegionManager::prepare_old_region_list_to_free(FreeRegionList* to_free_list,
+                                                        uint reserve_regions,
+                                                        uint free_regions_for_young_gen) {
+  assert(G1ElasticHeap, "Precondition");
+  assert_at_safepoint(true /* should_be_vm_thread */);
+  assert(to_free_list->is_empty(), "sanity");
+
+  G1CollectedHeap* g1h = G1CollectedHeap::heap();
+  assert(!g1h->elastic_heap()->in_conc_cycle(), "Precondition");
+
+  if (_free_list.length() <= (reserve_regions + free_regions_for_young_gen)) {
+    // Not enough free regions
+    return;
+  }
+
+  uint uncommit_regions = _free_list.length() - reserve_regions - free_regions_for_young_gen;
+  FreeRegionListIterator iter(&_free_list);
+  // Skip reserve regions from the head of _free_list
+  for (uint i = 0; i < reserve_regions; i++) {
+    assert(iter.more_available(), "sanity");
+    iter.get_next();
+  }
+  // Remove regions out of free list for uncommit
+  for (uint i = 0; i < uncommit_regions; i++) {
+    assert(iter.more_available(), "sanity");
+    HeapRegion* hr = iter.remove_next();
+    to_free_list->add_ordered(hr);
+  }
+  set_region_unavailable(to_free_list);
+}
+
 uint HeapRegionManager::shrink_by(uint num_regions_to_remove) {
   assert(length() > 0, "the region sequence should not be empty");
   assert(length() <= _allocated_heapregions_length, "invariant");

src/share/vm/gc_implementation/g1/heapRegionManager.hpp

@@ -79,6 +79,7 @@ class HeapRegionManager: public CHeapObj<mtGC> {
 
   FreeRegionList _free_list;
 
+  FreeRegionList _uncommitted_list;
   // Each bit in this bitmap indicates that the corresponding region is available
   // for allocation.
   BitMap _available_map;
@@ -131,7 +132,8 @@ public:
   HeapRegionManager() : _regions(), _heap_mapper(NULL), _num_committed(0),
                     _next_bitmap_mapper(NULL), _prev_bitmap_mapper(NULL), _bot_mapper(NULL),
                     _allocated_heapregions_length(0), _available_map(),
-                    _free_list("Free list", new MasterFreeRegionListMtSafeChecker())
+                    _free_list("Free list", new MasterFreeRegionListMtSafeChecker()),
+                    _uncommitted_list("Free list of uncommitted regions", new MasterFreeRegionListMtSafeChecker())
   { }
 
   void initialize(G1RegionToSpaceMapper* heap_storage,
@@ -232,6 +234,34 @@ public:
   // Return the actual number of uncommitted regions.
   uint shrink_by(uint num_regions_to_remove);
 
+  // Number of regions in uncommitted free list
+  uint num_uncommitted_regions();
+  // Move uncommitted regions back into free list
+  void recover_uncommitted_regions();
+
+  // Move regions into uncommitted list
+  void move_to_uncommitted_list(FreeRegionList* list);
+  // Move regions back into free list
+  void move_to_free_list(FreeRegionList* list);
+
+  // Remove regions from free list for uncommitment
+  void prepare_uncommit_regions(FreeRegionList* list, uint num);
+  // Remove regions from uncommitted list for commitment
+  void prepare_commit_regions(FreeRegionList* list, uint num);
+  // Remove old regions to free
+  void prepare_old_region_list_to_free(FreeRegionList* to_free_list,
+                                       uint reserve_regions,
+                                       uint free_regions_for_young_gen);
+
+  void commit_region_memory(FreeRegionList* list);
+  void uncommit_region_memory(FreeRegionList* list);
+  void set_region_available(FreeRegionList* list);
+  void set_region_unavailable(FreeRegionList* list);
+
+  void commit_region_memory(uint idx);
+  void uncommit_region_memory(uint idx);
+  void free_region_memory(uint idx);
+
   void verify();
 
   // Do some sanity checking.

src/share/vm/gc_implementation/g1/heapRegionSet.hpp

@@ -214,6 +214,9 @@ private:
   inline HeapRegion* remove_from_head_impl();
   inline HeapRegion* remove_from_tail_impl();
 
+  // Only called in FreeRegionListIterator so make it private
+  HeapRegion* remove_region(HeapRegion* hr);
+
 protected:
   virtual void fill_in_ext_msg_extra(hrs_ext_msg* msg);
 
@@ -287,6 +290,19 @@ public:
     return hr;
   }
 
+  HeapRegion* remove_next() {
+    assert(more_available(),
+           "remove_next() should be called when more regions are available");
+
+    HeapRegion* hr = _curr;
+    _list->verify_region(hr);
+
+    _curr = hr->next();
+
+    hr = _list->remove_region(hr);
+    return hr;
+  }
+
   FreeRegionListIterator(FreeRegionList* list) : _curr(NULL), _list(list) {
     _curr = list->_head;
   }

src/share/vm/gc_implementation/g1/heapRegionSet.inline.hpp

@@ -148,5 +148,40 @@ inline HeapRegion* FreeRegionList::remove_region(bool from_head) {
   return hr;
 }
 
+inline HeapRegion* FreeRegionList::remove_region(HeapRegion* hr) {
+  check_mt_safety();
+  verify_optional();
+
+  HeapRegion* prev = hr->prev();
+  HeapRegion* next = hr->next();
+
+  if (prev) {
+    prev->set_next(next);
+  } else {
+    // hr is _head
+    assert(_head == hr, "Sanity");
+    _head = next;
+  }
+
+  if (next) {
+    next->set_prev(prev);
+  } else {
+    // hr is _tail
+    assert(_tail == hr, "Sanity");
+    _tail = prev;
+  }
+
+  hr->set_prev(NULL);
+  hr->set_next(NULL);
+
+  if (_last == hr) {
+    _last = NULL;
+  }
+
+  // remove() will verify the region and check mt safety.
+  remove(hr);
+  return hr;
+}
+
 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_HEAPREGIONSET_INLINE_HPP
 

src/share/vm/gc_interface/gcCause.cpp

@@ -100,6 +100,9 @@ const char* GCCause::to_string(GCCause::Cause cause) {
     case _g1_humongous_allocation:
       return "G1 Humongous Allocation";
 
+    case _g1_elastic_heap_trigger_gc:
+      return "Elastic Heap triggered GC";
+
     case _last_ditch_collection:
       return "Last ditch collection";
 

src/share/vm/gc_interface/gcCause.hpp

@@ -73,6 +73,8 @@ class GCCause : public AllStatic {
     _g1_inc_collection_pause,
     _g1_humongous_allocation,
 
+    _g1_elastic_heap_trigger_gc,
+
     _last_ditch_collection,
     _last_gc_cause
   };

src/share/vm/prims/jvm.cpp

@@ -78,6 +78,8 @@
 #include "utilities/histogram.hpp"
 #include "utilities/top.hpp"
 #include "utilities/utf8.hpp"
+#include "gc_implementation/g1/g1CollectedHeap.hpp"
+#include "gc_implementation/g1/elasticHeap.hpp"
 #ifdef TARGET_OS_FAMILY_linux
 # include "jvm_linux.h"
 #endif
@@ -4748,3 +4750,89 @@ JVM_ENTRY(void, JVM_NotifyJVMDeoptWarmUpMethods(JNIEnv *env, jclass clazz))
   }
 }
 JVM_END
+
+JVM_ENTRY(jint, JVM_ElasticHeapGetEvaluationMode(JNIEnv *env, jclass klass))
+  JVMWrapper("JVM_ElasticHeapGetEvaluationMode");
+  assert(G1ElasticHeap, "Precondition");
+
+  return G1CollectedHeap::heap()->elastic_heap()->evaluation_mode();
+JVM_END
+
+JVM_ENTRY(void, JVM_ElasticHeapSetYoungGenCommitPercent(JNIEnv *env, jclass klass, jint percent))
+  JVMWrapper("JVM_ElasticHeapSetYoungGenCommitPercent");
+  assert(G1ElasticHeap, "Precondition");
+
+  ElasticHeap* elas = G1CollectedHeap::heap()->elastic_heap();
+  ElasticHeap::ErrorType error = elas->configure_setting(percent, ElasticHeap::ignore_arg(),
+                                                           ElasticHeap::ignore_arg());
+
+  if (error == ElasticHeap::IllegalYoungPercent) {
+    char as_chars[256];
+    jio_snprintf(as_chars, sizeof(as_chars), "percent should be 0, or between %u and 100 ", ElasticHeapMinYoungCommitPercent);
+    THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), as_chars);
+  } else if (error != ElasticHeap::NoError) {
+    THROW_MSG(vmSymbols::java_lang_IllegalStateException(), ElasticHeap::to_string(error));
+  }
+JVM_END
+
+JVM_ENTRY(jint, JVM_ElasticHeapGetYoungGenCommitPercent(JNIEnv *env, jclass klass))
+  JVMWrapper("JVM_ElasticHeapGetYoungGenCommitPercent");
+  assert(G1ElasticHeap, "Precondition");
+
+  return G1CollectedHeap::heap()->elastic_heap()->young_commit_percent();
+JVM_END
+
+JVM_ENTRY(void, JVM_ElasticHeapSetUncommitIHOP(JNIEnv *env, jclass klass, jint percent))
+  JVMWrapper("JVM_ElasticHeapSetUncommitIHOP");
+  assert(G1ElasticHeap, "Precondition");
+  assert(percent >= 0 && percent <= 100, "sanity");
+
+  ElasticHeap* elas = G1CollectedHeap::heap()->elastic_heap();
+  ElasticHeap::ErrorType error = elas->configure_setting(ElasticHeap::ignore_arg(), percent,
+                                                           ElasticHeap::ignore_arg());
+  if (error != ElasticHeap::NoError) {
+    THROW_MSG(vmSymbols::java_lang_IllegalStateException(), ElasticHeap::to_string(error));
+  }
+JVM_END
+
+JVM_ENTRY(jint, JVM_ElasticHeapGetUncommitIHOP(JNIEnv *env, jclass klass))
+  JVMWrapper("JVM_ElasticHeapGetUncommitIHOP");
+  assert(G1ElasticHeap, "Precondition");
+
+  return G1CollectedHeap::heap()->elastic_heap()->uncommit_ihop();
+JVM_END
+
+JVM_ENTRY(jlong, JVM_ElasticHeapGetTotalYoungUncommittedBytes(JNIEnv *env, jclass klass))
+  JVMWrapper("JVM_ElasticHeapGetTotalYoungUncommittedBytes");
+  assert(G1ElasticHeap, "Precondition");
+
+  return G1CollectedHeap::heap()->elastic_heap()->young_uncommitted_bytes();
+JVM_END
+
+JVM_ENTRY(void, JVM_ElasticHeapSetSoftmxPercent(JNIEnv *env, jclass klass, jint percent))
+  JVMWrapper("JVM_ElasticHeapSetSoftmxPercent");
+  assert(G1ElasticHeap, "Precondition");
+  assert(percent >= 0 && percent <= 100, "sanity");
+
+  ElasticHeap* elas = G1CollectedHeap::heap()->elastic_heap();
+
+  ElasticHeap::ErrorType error = elas->configure_setting(ElasticHeap::ignore_arg(),
+                                                           ElasticHeap::ignore_arg(), percent);
+  if (error != ElasticHeap::NoError) {
+    THROW_MSG(vmSymbols::java_lang_IllegalStateException(), ElasticHeap::to_string(error));
+  }
+JVM_END
+
+JVM_ENTRY(jint, JVM_ElasticHeapGetSoftmxPercent(JNIEnv *env, jclass klass))
+  JVMWrapper("JVM_ElasticHeapGetSoftmxPercent");
+  assert(G1ElasticHeap, "Precondition");
+
+  return G1CollectedHeap::heap()->elastic_heap()->softmx_percent();
+JVM_END
+
+JVM_ENTRY(jlong, JVM_ElasticHeapGetTotalUncommittedBytes(JNIEnv *env, jclass klass))
+  JVMWrapper("JVM_ElasticHeapGetTotalUncommittedBytes");
+  assert(G1ElasticHeap, "Precondition");
+
+  return G1CollectedHeap::heap()->elastic_heap()->uncommitted_bytes();
+JVM_END

src/share/vm/prims/jvm.h

@@ -1714,6 +1714,28 @@ JVM_CheckJWarmUpCompilationIsComplete(JNIEnv* env, jclass ignored);
 JNIEXPORT void JNICALL
 JVM_NotifyJVMDeoptWarmUpMethods(JNIEnv* env, jclass clz);
 
+/*
+ * com.alibaba.management.ElasticHeapMXBeanImpl
+ */
+JNIEXPORT jint JNICALL
+JVM_ElasticHeapGetEvaluationMode(JNIEnv *env, jclass clazz);
+JNIEXPORT void JNICALL
+JVM_ElasticHeapSetYoungGenCommitPercent(JNIEnv *env, jclass klass, jint percent);
+JNIEXPORT jint JNICALL
+JVM_ElasticHeapGetYoungGenCommitPercent(JNIEnv *env, jclass klass);
+JNIEXPORT void JNICALL
+JVM_ElasticHeapSetUncommitIHOP(JNIEnv *env, jclass clazz, jint percent);
+JNIEXPORT jint JNICALL
+JVM_ElasticHeapGetUncommitIHOP(JNIEnv *env, jclass clazz);
+JNIEXPORT jlong JNICALL
+JVM_ElasticHeapGetTotalYoungUncommittedBytes(JNIEnv *env, jclass klass);
+JNIEXPORT void JNICALL
+JVM_ElasticHeapSetSoftmxPercent(JNIEnv *env, jclass clazz, jint percent);
+JNIEXPORT jint JNICALL
+JVM_ElasticHeapGetSoftmxPercent(JNIEnv *env, jclass clazz);
+JNIEXPORT jlong JNICALL
+JVM_ElasticHeapGetTotalUncommittedBytes(JNIEnv *env, jclass clazz);
+
 #ifdef __cplusplus
 } /* extern "C" */
 #endif /* __cplusplus */

src/share/vm/runtime/arguments.cpp

@@ -2293,6 +2293,33 @@ bool Arguments::check_vm_args_consistency() {
   // Note: Needs platform-dependent factoring.
   bool status = true;
 
+  if (G1ElasticHeap) {
+    if (!UseG1GC) {
+      vm_exit_during_initialization("G1ElasticHeap only works with UseG1GC");
+    }
+    status = status && verify_interval(ElasticHeapMinYoungCommitPercent, 1, 100, "ElasticHeapMinYoungCommitPercent");
+    status = status && verify_interval(ElasticHeapPeriodicMinYoungCommitPercent, ElasticHeapMinYoungCommitPercent, 100, "ElasticHeapMinYoungCommitPercentAuto");
+    PropertyList_unique_add(&_system_properties, "com.alibaba.jvm.gc.ElasticHeapEnabled", (char*)"true");
+    status = status && verify_interval(ElasticHeapOldGenReservePercent, 1, 100, "ElasticHeapOldGenReservePercent");
+
+    if (InitialHeapSize != MaxHeapSize) {
+      jio_fprintf(defaultStream::error_stream(),
+                  "G1ElasticHeap requires Xms:"
+                  SIZE_FORMAT
+                  " bytes same to Xmx: "
+                  SIZE_FORMAT
+                  " bytes",
+                  InitialHeapSize, MaxHeapSize);
+      status = false;
+    }
+  }
+
+  if (ElasticHeapPeriodicUncommit) {
+    if (!G1ElasticHeap) {
+      vm_exit_during_initialization("ElasticHeapPeriodicUncommit only works with G1ElasticHeap");
+    }
+  }
+
   // Allow both -XX:-UseStackBanging and -XX:-UseBoundThreads in non-product
   // builds so the cost of stack banging can be measured.
 #if (defined(PRODUCT) && defined(SOLARIS))

src/share/vm/runtime/globals_ext.hpp

@@ -38,6 +38,62 @@
              "Desired size of array space allocation before "               \
              "printing a warning")                                          \
                                                                             \
+  product(bool, G1ElasticHeap, false,                                       \
+          "Allow java heap to be resized in runtime")                       \
+                                                                            \
+  manageable(uintx, ElasticHeapMinYoungCommitPercent, 10,                   \
+          "Minimal commit percentage of young gen size")                    \
+          /* Similar to G1NewSizePercent/G1MaxNewSizePercent */             \
+                                                                            \
+  manageable(uintx, ElasticHeapYGCIntervalMinMillis, 5000,                  \
+          "Might uncommit memory only if young GC interval "                \
+          "larger than this threshold in milliseconds ")                    \
+                                                                            \
+  manageable(uintx, ElasticHeapInitialMarkIntervalMinMillis, 60000,         \
+          "Might uncommit memory only if initial mark interval "            \
+          "larger than this threshold in milliseconds ")                    \
+                                                                            \
+  manageable(bool, ElasticHeapPeriodicUncommit, false,                      \
+          "Uncommit memory by periodic GC")                                 \
+                                                                            \
+  manageable(uintx, ElasticHeapPeriodicUncommitStartupDelay, 300,           \
+          "Starup delay in seconds for periodic uncommit")                  \
+                                                                            \
+  manageable(uintx, ElasticHeapPeriodicMinYoungCommitPercent, 50,           \
+          "Minimal commit percentage of young gen in periodic gc mode")     \
+                                                                            \
+  manageable(uintx, ElasticHeapPeriodicYGCIntervalMillis, 15000,            \
+          "Target young gc interval in milliseconds after "                 \
+          "resizing young gen in periodic gc mode")                         \
+                                                                            \
+  manageable(uintx, ElasticHeapPeriodicInitialMarkIntervalMillis, 3600000,  \
+          "Target initial mark interval "                                   \
+          "in milliseconds in periodic gc mode. "                           \
+          "Free regions after mixed gc will be uncommitted. ")              \
+                                                                            \
+  manageable(uintx, ElasticHeapPeriodicYGCIntervalCeilingPercent, 25,       \
+          "Ceiling percent of the young gc inverval larger than "           \
+          "ElasticHeapPeriodicYGCIntervalMillis")                           \
+                                                                            \
+  manageable(uintx, ElasticHeapPeriodicYGCIntervalFloorPercent, 25,         \
+          "Floor percent of the young gc interval less than "               \
+          "ElasticHeapPeriodicYGCIntervalMillis")                           \
+                                                                            \
+  manageable(uintx, ElasticHeapEagerMixedGCIntervalMillis, 15000,           \
+          "Mixed GC will be triggered if desired mixed gc doesn't happen "  \
+          "after the interval in milliseconds")                             \
+                                                                            \
+  manageable(uintx, ElasticHeapOldGenReservePercent, 5,                     \
+          "Percentage(0-100) of heap size to be reserved for "              \
+          "old gen to grow")                                                \
+                                                                            \
+  manageable(bool, PrintElasticHeapDetails, true,                           \
+          "Print Elastic Heap detail information in GC log")                \
+                                                                            \
+  product(uintx, ElasticHeapParallelWorkers, 0,                             \
+          "Number of parallel worker threads for memory "                   \
+          "commit/uncommit. 0 be same as ConcGCThreads")                    \
+
   //add new AJVM specific flags here
 
 

src/share/vm/runtime/thread.cpp

@@ -102,6 +102,7 @@
 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
 #include "gc_implementation/g1/concurrentMarkThread.inline.hpp"
 #include "gc_implementation/parallelScavenge/pcTasks.hpp"
+#include "gc_implementation/g1/elasticHeap.hpp"
 #endif // INCLUDE_ALL_GCS
 #ifdef COMPILER1
 #include "c1/c1_Compiler.hpp"
@@ -3625,6 +3626,12 @@ jint Threads::create_vm(JavaVMInitArgs* args, bool* canTryAgain) {
       vm_exit_during_initialization(Handle(THREAD, PENDING_EXCEPTION));
     }
   }
+  if (G1ElasticHeap) {
+    ElasticHeapTimer::start();
+    if (HAS_PENDING_EXCEPTION) {
+      vm_exit_during_initialization(Handle(THREAD, PENDING_EXCEPTION));
+    }
+  }
 #endif // INCLUDE_ALL_GCS
 
   // Always call even when there are not JVMTI environments yet, since environments

src/share/vm/services/attachListener.cpp

@@ -36,6 +36,8 @@
 #include "services/attachListener.hpp"
 #include "services/diagnosticCommand.hpp"
 #include "services/heapDumper.hpp"
+#include "gc_implementation/g1/g1CollectedHeap.hpp"
+#include "gc_implementation/g1/elasticHeap.hpp"
 
 volatile bool AttachListener::_initialized;
 
@@ -257,6 +259,13 @@ static jint set_bool_flag(const char* name, AttachOperation* op, outputStream* o
     }
     value = (tmp != 0);
   }
+  if (strcmp(name, "ElasticHeapPeriodicUncommit") == 0 & value) {
+    if (G1ElasticHeap &&
+        !G1CollectedHeap::heap()->elastic_heap()->can_turn_on_periodic_uncommit()) {
+      out->print_cr("cannot be set because of illegal state.");
+      return JNI_ERR;
+    }
+  }
   bool res = CommandLineFlags::boolAtPut((char*)name, &value, Flag::ATTACH_ON_DEMAND);
   if (! res) {
     out->print_cr("setting flag %s failed", name);
@@ -312,6 +321,16 @@ static jint set_uintx_flag(const char* name, AttachOperation* op, outputStream*
       return JNI_ERR;
     }
   }
+
+  if (strcmp(name, "ElasticHeapMinYoungCommitPercent") == 0 ||
+      strcmp(name, "ElasticHeapPeriodicMinYoungCommitPercent") == 0 ||
+      strcmp(name, "ElasticHeapPeriodicYGCIntervalCeilingPercent") == 0 ||
+      strcmp(name, "ElasticHeapPeriodicYGCIntervalFloorPercent") == 0) {
+    if (value < 1 || value > 100) {
+      out->print_cr("%s must be between 1 and 100", name);
+      return JNI_ERR;
+    }
+  }
   bool res = CommandLineFlags::uintxAtPut((char*)name, &value, Flag::ATTACH_ON_DEMAND);
   if (! res) {
     out->print_cr("setting flag %s failed", name);

src/share/vm/services/diagnosticCommand.cpp

@@ -34,6 +34,7 @@
 #include "services/management.hpp"
 #include "utilities/macros.hpp"
 #include "oops/objArrayOop.hpp"
+#include "gc_implementation/g1/elasticHeap.hpp"
 
 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
 
@@ -73,6 +74,7 @@ void DCmdRegistrant::register_dcmds(){
   DCmdFactory::register_DCmdFactory(new DCmdFactoryImpl<JMXStartLocalDCmd>(jmx_agent_export_flags, true,false));
   DCmdFactory::register_DCmdFactory(new DCmdFactoryImpl<JMXStopRemoteDCmd>(jmx_agent_export_flags, true,false));
 
+  DCmdFactory::register_DCmdFactory(new DCmdFactoryImpl<ElasticHeapDCmd>(full_export, true, false));
 }
 
 #ifndef HAVE_EXTRA_DCMD
@@ -849,3 +851,114 @@ void JWarmupDCmd::print_info() {
                        "-help: %s\n",
                        _notify_startup.description(), _check_compile_finished.description(), _deopt.description(), _help.description());
 }
+
+ElasticHeapDCmd::ElasticHeapDCmd(outputStream* output, bool heap) :
+                           DCmdWithParser(output, heap),
+    _young_commit_percent("young_commit_percent",
+                          "Percentage of committed size in young generation to be adjusted to",
+                          "INT", false),
+    _uncommit_ihop("uncommit_ihop",
+                   "Percentage of heap to trigger concurrent mark to uncommit memory",
+                   "INT", false),
+    _softmx_percent("softmx_percent",
+                         "Percentage of committed size of heap to be adjusted to",
+                         "INT", false) {
+  _dcmdparser.add_dcmd_option(&_young_commit_percent);
+  _dcmdparser.add_dcmd_option(&_uncommit_ihop);
+  _dcmdparser.add_dcmd_option(&_softmx_percent);
+}
+
+int ElasticHeapDCmd::num_arguments() {
+  ResourceMark rm;
+  int num_args = 0;
+  ElasticHeapDCmd* dcmd = new ElasticHeapDCmd(NULL, false);
+
+  if (dcmd != NULL) {
+    DCmdMark mark(dcmd);
+    num_args = dcmd->_dcmdparser.num_arguments();
+  }
+
+  return num_args;
+}
+
+bool ElasticHeapDCmd::illegal_percent(uint percent, const char* name) {
+  if (percent > 100) {
+    output()->print_cr("Error: %s between 0 and 100.", name);
+    print_info();
+    return true;
+  }
+  return false;
+}
+
+void ElasticHeapDCmd::execute(DCmdSource source, TRAPS) {
+  if (!G1ElasticHeap) {
+    output()->print_cr("Error: -XX:+G1ElasticHeap is not enabled!");
+    return;
+  }
+
+  uint young_percent= ElasticHeap::ignore_arg();
+  uint uncommit_ihop = ElasticHeap::ignore_arg();
+  uint softmx_percent = ElasticHeap::ignore_arg();
+  bool option_set = false;
+
+  if (_young_commit_percent.is_set()) {
+    young_percent = _young_commit_percent.value();
+    option_set = true;
+  }
+  if (_uncommit_ihop.is_set()) {
+    uncommit_ihop = _uncommit_ihop.value();
+    if (illegal_percent(uncommit_ihop, "uncommit_ihop")) {
+      return;
+    }
+    option_set = true;
+  }
+  if (_softmx_percent.is_set()) {
+    if (_young_commit_percent.is_set() || _uncommit_ihop.is_set()) {
+      output()->print_cr("Error: softmx_percent should be set alone!");
+      print_info();
+      return;
+    }
+    softmx_percent = _softmx_percent.value();
+    if (illegal_percent(softmx_percent, "softmx_percent")) {
+      return;
+    }
+    option_set = true;
+  }
+
+  if (option_set) {
+    ElasticHeap::ErrorType error = G1CollectedHeap::heap()->elastic_heap()->configure_setting(young_percent, uncommit_ihop, softmx_percent);
+    if (error == ElasticHeap::IllegalMode) {
+      output()->print_cr("Error: not in correct mode.");
+    } else if (error == ElasticHeap::IllegalYoungPercent) {
+      output()->print_cr("Error: young_commit_percent should be 0, or between %d and 100", ElasticHeapMinYoungCommitPercent);
+    } else if (error != ElasticHeap::NoError) {
+      output()->print_cr("Error: command fails because %s", ElasticHeap::to_string(error));
+    } else {
+      // Success
+    }
+  }
+  print_info();
+}
+
+void ElasticHeapDCmd::print_info() {
+  uint percent;
+  jlong uncommitted_bytes;
+  ElasticHeap::EvaluationMode mode = G1CollectedHeap::heap()->elastic_heap()->evaluation_mode();
+  switch (mode) {
+    case ElasticHeap::InactiveMode:
+      output()->print_cr("[GC.elastic_heap: inactive]");
+      break;
+    case ElasticHeap::SoftmxMode:
+      output()->print_cr("[GC.elastic_heap: in %s mode]", ElasticHeap::to_string(mode));
+      percent = G1CollectedHeap::heap()->elastic_heap()->softmx_percent();
+      uncommitted_bytes = G1CollectedHeap::heap()->elastic_heap()->uncommitted_bytes();
+      output()->print_cr("[GC.elastic_heap: softmx percent %d, uncommitted memory %ld B]", percent, uncommitted_bytes);
+      break;
+    default:
+      output()->print_cr("[GC.elastic_heap: in %s mode]", ElasticHeap::to_string(mode));
+      percent = G1CollectedHeap::heap()->elastic_heap()->young_commit_percent();
+      uncommitted_bytes = G1CollectedHeap::heap()->elastic_heap()->young_uncommitted_bytes();
+      output()->print_cr("[GC.elastic_heap: young generation commit percent %d, uncommitted memory %ld B]", percent, uncommitted_bytes);
+      break;
+  }
+}

src/share/vm/services/diagnosticCommand.hpp

@@ -461,4 +461,23 @@ public:
   virtual void execute(DCmdSource source, TRAPS);
 };
 
+class ElasticHeapDCmd : public DCmdWithParser {
+protected:
+  DCmdArgument<jlong> _young_commit_percent;
+  DCmdArgument<jlong> _uncommit_ihop;
+  DCmdArgument<jlong> _softmx_percent;
+  void print_info();
+  bool illegal_percent(uint percent, const char* name);
+public:
+  ElasticHeapDCmd(outputStream* output, bool heap_allocated);
+  static const char* name() {
+    return "GC.elastic_heap";
+  }
+  static const char* description() {
+    return "Elastic Heap Command";
+  }
+  static int num_arguments();
+  virtual void execute(DCmdSource source, TRAPS);
+};
+
 #endif // SHARE_VM_SERVICES_DIAGNOSTICCOMMAND_HPP

test/elastic-heap/TestElasticHeapConflictCommand.java

+/*
+ * Copyright (c) 2019 Alibaba Group Holding Limited. All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Alibaba designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+import java.io.File;
+import com.oracle.java.testlibrary.*;
+
+/* @test
+ * @summary test elastic-heap conflict commands
+ * @library /testlibrary
+ * @build TestElasticHeapConflictCommand
+ * @run main/othervm/timeout=200
+         -XX:+UseG1GC -XX:+G1ElasticHeap -Xmx1000m -Xms1000m
+                -XX:ElasticHeapPeriodicYGCIntervalMillis=400
+                -XX:ElasticHeapPeriodicUncommitStartupDelay=0
+                -Xmn200m -XX:G1HeapRegionSize=1m -XX:+AlwaysPreTouch
+                -XX:ElasticHeapYGCIntervalMinMillis=50
+                -verbose:gc -XX:+PrintGCDetails -XX:+PrintGCTimeStamps
+                TestElasticHeapConflictCommand
+ */
+
+public class TestElasticHeapConflictCommand {
+    public static void main(String[] args) throws Exception {
+        OutputAnalyzer output;
+        byte[] arr = new byte[200*1024];
+        // Allocate 200k per 1ms , 200M per second
+        // so 2 GCs per second
+        for (int i = 0; i < 1000 * 3; i++) {
+            arr = new byte[200*1024];
+            Thread.sleep(1);
+        }
+        int rssFull = getRss();
+        System.out.println("rssFull: " + rssFull);
+
+        output = triggerJinfo("+ElasticHeapPeriodicUncommit");
+        output.shouldHaveExitValue(0);
+        // Allocate 200k per ms , 200M per second
+        // so 1 GC per second
+        for (int i = 0; i < 1000 * 5; i++) {
+            arr = new byte[200*1024];
+            Thread.sleep(1);
+        }
+
+        output = triggerJcmd("GC.elastic_heap", "young_commit_percent=50");
+        System.out.println(output.getOutput());
+        output.shouldContain("Error: not in correct mode");
+        output.shouldHaveExitValue(0);
+
+        output = triggerJcmd("GC.elastic_heap", "uncommit_ihop=50");
+        System.out.println(output.getOutput());
+        output.shouldContain("Error: not in correct mode");
+        output.shouldHaveExitValue(0);
+
+        output = triggerJcmd("GC.elastic_heap", "softmx_percent=50");
+        System.out.println(output.getOutput());
+        output.shouldContain("not in correct mode");
+        output.shouldHaveExitValue(0);
+
+        output = triggerJinfo("-ElasticHeapPeriodicUncommit");
+        output.shouldHaveExitValue(0);
+        // Allocate 200k per ms , 200M per second
+        // so 1 GC per second
+        for (int i = 0; i < 1000 * 5; i++) {
+            arr = new byte[200*1024];
+            Thread.sleep(1);
+        }
+
+        output = triggerJcmd("GC.elastic_heap", "young_commit_percent=50");
+        System.out.println(output.getOutput());
+        output.shouldContain("[GC.elastic_heap: young generation commit percent 50, uncommitted memory 104857600 B]");
+        output.shouldHaveExitValue(0);
+
+        output = triggerJinfo("+ElasticHeapPeriodicUncommit");
+        System.out.println(output.getOutput());
+        output.shouldContain("cannot be set because of illegal state");
+        output.shouldHaveExitValue(1);
+
+        output = triggerJcmd("GC.elastic_heap", "softmx_percent=80");
+        System.out.println(output.getOutput());
+        output.shouldContain("Error: not in correct mode");
+        output.shouldHaveExitValue(0);
+
+
+        // Allocate 200k per ms , 200M per second
+        // so 1 GC per second
+        for (int i = 0; i < 1000 * 5; i++) {
+            arr = new byte[200*1024];
+            Thread.sleep(1);
+        }
+        output = triggerJcmd("GC.elastic_heap", "young_commit_percent=0", "uncommit_ihop=30");
+        System.out.println(output.getOutput());
+        output.shouldContain("[GC.elastic_heap: young generation commit percent 100, uncommitted memory 0 B]");
+        output.shouldHaveExitValue(0);
+
+        // Allocate 200k per ms , 200M per second
+        // so 1 GC per second
+        for (int i = 0; i < 1000 * 5; i++) {
+            arr = new byte[200*1024];
+            Thread.sleep(1);
+        }
+        output = triggerJinfo("+ElasticHeapPeriodicUncommit");
+        System.out.println(output.getOutput());
+        output.shouldContain("cannot be set because of illegal state");
+        output.shouldHaveExitValue(1);
+
+        output = triggerJcmd("GC.elastic_heap", "softmx_percent=80");
+        System.out.println(output.getOutput());
+        output.shouldContain("Error: not in correct mode");
+        output.shouldHaveExitValue(0);
+
+        output = triggerJcmd("GC.elastic_heap", "uncommit_ihop=0");
+        System.out.println(output.getOutput());
+        output.shouldContain("[GC.elastic_heap: inactive]");
+        output.shouldHaveExitValue(0);
+        // Allocate 200k per ms , 200M per second
+        // so 1 GC per second
+        for (int i = 0; i < 1000 * 5; i++) {
+            arr = new byte[200*1024];
+            Thread.sleep(1);
+        }
+
+        output = triggerJcmd("GC.elastic_heap", "softmx_percent=80");
+        System.out.println(output.getOutput());
+        output.shouldContain("in softmx mode");
+        output.shouldHaveExitValue(0);
+        // Allocate 400k per ms , 400M per second
+        // so 2 GC per second
+        for (int i = 0; i < 1000 * 5; i++) {
+            arr = new byte[200*1024];
+            arr = new byte[200*1024];
+            Thread.sleep(1);
+        }
+
+        output = triggerJinfo("+ElasticHeapPeriodicUncommit");
+        System.out.println(output.getOutput());
+        output.shouldContain("cannot be set because of illegal state");
+        output.shouldHaveExitValue(1);
+
+        output = triggerJcmd("GC.elastic_heap", "young_commit_percent=80");
+        System.out.println(output.getOutput());
+        output.shouldContain("Error: not in correct mode");
+        output.shouldHaveExitValue(0);
+
+        output = triggerJcmd("GC.elastic_heap", "uncommit_ihop=30");
+        System.out.println(output.getOutput());
+        output.shouldContain("Error: not in correct mode");
+        output.shouldHaveExitValue(0);
+    }
+
+    private static OutputAnalyzer triggerJcmd(String arg1, String arg2) throws Exception {
+        return triggerJcmd(arg1, arg2, null);
+    }
+    private static OutputAnalyzer triggerJcmd(String arg1, String arg2, String arg3) throws Exception {
+        String pid = Integer.toString(ProcessTools.getProcessId());
+        JDKToolLauncher jcmd = JDKToolLauncher.create("jcmd").addToolArg(pid);
+        if (arg1 != null) {
+            jcmd.addToolArg(arg1);
+        }
+        if (arg2 != null) {
+            jcmd.addToolArg(arg2);
+        }
+        if (arg3 != null) {
+            jcmd.addToolArg(arg3);
+        }
+        ProcessBuilder pb = new ProcessBuilder(jcmd.getCommand());
+        return new OutputAnalyzer(pb.start());
+    }
+
+    private static OutputAnalyzer triggerJinfo(String arg) throws Exception {
+        String pid = Integer.toString(ProcessTools.getProcessId());
+        JDKToolLauncher jcmd = JDKToolLauncher.create("jinfo")
+                                              .addToolArg("-flag")
+                                              .addToolArg(arg)
+                                              .addToolArg(pid);
+        ProcessBuilder pb = new ProcessBuilder(jcmd.getCommand());
+        return new OutputAnalyzer(pb.start());
+    }
+    private static int getRss() throws Exception {
+        String pid = Integer.toString(ProcessTools.getProcessId());
+        int rss = 0;
+        Process ps = Runtime.getRuntime().exec("cat /proc/"+pid+"/status");
+        ps.waitFor();
+        BufferedReader br = new BufferedReader(new InputStreamReader(ps.getInputStream()));
+        String line;
+        while (( line = br.readLine()) != null ) {
+            if (line.startsWith("VmRSS:") ) {
+                int numEnd = line.length() - 3;
+                int numBegin = line.lastIndexOf(" ", numEnd - 1) + 1;
+                rss = Integer.parseInt(line.substring(numBegin, numEnd));
+                break;
+            }
+        }
+        return rss;
+    }
+}

test/elastic-heap/TestElasticHeapGenerationLimit.java

+/*
+ * Copyright (c) 2019 Alibaba Group Holding Limited. All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Alibaba designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+import java.io.File;
+import com.oracle.java.testlibrary.*;
+
+/* @test
+ * @summary test elastic-heap with jcmd
+ * @library /testlibrary
+ * @build TestElasticHeapGenerationLimit
+ * @run main/othervm/timeout=500
+         -XX:+UseG1GC -XX:+G1ElasticHeap -Xmx1000m -Xms1000m
+                -XX:MaxNewSize=400m -XX:G1HeapRegionSize=1m
+                -XX:ElasticHeapYGCIntervalMinMillis=500
+                -verbose:gc -XX:+PrintGCDetails -XX:+PrintGCTimeStamps
+                TestElasticHeapGenerationLimit
+ */
+
+public class TestElasticHeapGenerationLimit {
+    public static void main(String[] args) throws Exception {
+        for (int i = 0; i < 3; i++) {
+            test();
+        }
+    }
+    public static void test() throws Exception {
+        byte[] arr = new byte[200*1024];
+        OutputAnalyzer output;
+        // Allocate 200k per 1ms, 200M per second
+        // so 0.5 GCs per second
+        for (int i = 0; i < 1000 * 5; i++) {
+            arr = new byte[200*1024];
+            Thread.sleep(1);
+        }
+        int rssFull = getRss();
+        System.out.println("Full rss: " + rssFull);
+        System.gc();
+        output = triggerJcmd("GC.elastic_heap", "young_commit_percent=50");
+        System.out.println(output.getOutput());
+        output.shouldContain("[GC.elastic_heap: young generation commit percent 50, uncommitted memory 209715200 B]");
+        output.shouldHaveExitValue(0);
+        for (int i = 0; i < 1000 * 5; i++) {
+            arr = new byte[200*1024];
+            Thread.sleep(1);
+        }
+        int rss50 = getRss();
+        System.out.println("50% rss: " + rss50);
+        Asserts.assertTrue(rss50 < rssFull);
+        Asserts.assertTrue(Math.abs(rssFull - rss50) > 150 * 1024);
+
+        output = triggerJcmd("GC.elastic_heap", "young_commit_percent=100");
+        System.out.println(output.getOutput());
+        output.shouldContain("[GC.elastic_heap: young generation commit percent 100, uncommitted memory 0 B]");
+        output.shouldHaveExitValue(0);
+        for (int i = 0; i < 1000 * 5; i++) {
+            arr = new byte[200*1024];
+            Thread.sleep(1);
+        }
+        int rss100 = getRss();
+        System.out.println("100% rss: " + rss100);
+        Asserts.assertTrue(Math.abs(rss100 - rssFull) < 50 * 1024);
+        Asserts.assertTrue(Math.abs(rss100 - rss50) > 150 * 1024);
+
+        output = triggerJcmd("GC.elastic_heap", "young_commit_percent=0");
+        System.out.println(output.getOutput());
+        output.shouldContain("[GC.elastic_heap: inactive]");
+        for (int i = 0; i < 1000 * 5; i++) {
+            arr = new byte[200*1024];
+            Thread.sleep(1);
+        }
+        int rss0 = getRss();
+        System.out.println("Recover rss: " + rss0);
+        Asserts.assertTrue(Math.abs(rss0 - rssFull) < 50 * 1024);
+        Asserts.assertTrue(Math.abs(rss0 - rss50) > 150 * 1024);
+
+        output = triggerJcmd("GC.elastic_heap", "young_commit_percent=30");
+        System.out.println(output.getOutput());
+        output.shouldContain("[GC.elastic_heap: young generation commit percent 30, uncommitted memory 293601280 B]");
+        for (int i = 0; i < 1000 * 5; i++) {
+            arr = new byte[200*1024];
+            Thread.sleep(1);
+        }
+
+        System.gc();
+        int rss30 = getRss();
+        System.out.println("rss30: " + rss30);
+        Asserts.assertTrue(rss30 < rss50);
+        Asserts.assertTrue(Math.abs(rss30 - rssFull) > 250 * 1024);
+        for (int i = 0; i < 1000 * 5; i++) {
+            arr = new byte[200*1024];
+            arr = new byte[200*1024];
+            Thread.sleep(1);
+        }
+
+        output = triggerJcmd("GC.elastic_heap", "young_commit_percent=20");
+        System.out.println(output.getOutput());
+        output.shouldContain("gc is too frequent");
+        output = triggerJcmd("GC.elastic_heap", "young_commit_percent=40");
+        System.out.println(output.getOutput());
+        output.shouldContain("[GC.elastic_heap: young generation commit percent 40, uncommitted memory 251658240 B]");
+        for (int i = 0; i < 1000 * 3; i++) {
+            arr = new byte[200*1024];
+            arr = new byte[200*1024];
+            Thread.sleep(1);
+        }
+
+        output = triggerJcmd("GC.elastic_heap", "young_commit_percent=0");
+        System.out.println(output.getOutput());
+    }
+
+    private static OutputAnalyzer triggerJcmd(String arg1, String arg2) throws Exception {
+        String pid = Integer.toString(ProcessTools.getProcessId());
+        JDKToolLauncher jcmd = JDKToolLauncher.create("jcmd")
+                                              .addToolArg(pid);
+        if (arg1 != null) {
+            jcmd.addToolArg(arg1);
+        }
+        if (arg2 != null) {
+            jcmd.addToolArg(arg2);
+        }
+        ProcessBuilder pb = new ProcessBuilder(jcmd.getCommand());
+        return new OutputAnalyzer(pb.start());
+    }
+
+    private static int getRss() throws Exception {
+        String pid = Integer.toString(ProcessTools.getProcessId());
+        int rss = 0;
+        Process ps = Runtime.getRuntime().exec("cat /proc/"+pid+"/status");
+        ps.waitFor();
+        BufferedReader br = new BufferedReader(new InputStreamReader(ps.getInputStream()));
+        String line;
+        while (( line = br.readLine()) != null ) {
+            if (line.startsWith("VmRSS:") ) {
+                int numEnd = line.length() - 3;
+                int numBegin = line.lastIndexOf(" ", numEnd - 1) + 1;
+                rss = Integer.parseInt(line.substring(numBegin, numEnd));
+                break;
+            }
+        }
+        return rss;
+    }
+}

test/elastic-heap/TestElasticHeapGenerationLimitUncommitIhop.java

+/*
+ * Copyright (c) 2019 Alibaba Group Holding Limited. All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Alibaba designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+import java.io.File;
+import com.oracle.java.testlibrary.*;
+
+/* @test
+ * @summary test elastic-heap with jcmd
+ * @library /testlibrary
+ * @build TestElasticHeapGenerationLimitUncommitIhop
+ * @run main/othervm/timeout=200 -XX:+UseG1GC -XX:+G1ElasticHeap -Xmx1000m -Xms1000m -XX:MaxNewSize=400m -XX:G1HeapRegionSize=1m -XX:ElasticHeapEagerMixedGCIntervalMillis=1000 -XX:ElasticHeapInitialMarkIntervalMinMillis=0 -XX:+AlwaysPreTouch -verbose:gc -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+PrintGCDateStamps -XX:ElasticHeapYGCIntervalMinMillis=10 TestElasticHeapGenerationLimitUncommitIhop
+ */
+
+public class TestElasticHeapGenerationLimitUncommitIhop {
+    public static void main(String[] args) throws Exception {
+        byte[] arr = new byte[200*1024];
+        OutputAnalyzer output;
+        // Promote 480M into old gen
+        Object[] root = new Object[5 * 1024];
+        for (int i = 0; i < 1000 * 5 - 200; i++) {
+            root[i] = new byte[100*1024];
+            Thread.sleep(1);
+        }
+        System.gc();
+        int rssFull = getRss();
+        System.out.println("Full rss: " + rssFull);
+        root = null;
+        output = triggerJcmd("GC.elastic_heap", "uncommit_ihop=30", "young_commit_percent=50");
+        System.out.println(output.getOutput());
+        output.shouldContain("[GC.elastic_heap: young generation commit percent 50, uncommitted memory 209715200 B]");
+        output.shouldHaveExitValue(0);
+        // Guaranteed gc will happen and mixed gc will finish
+        for (int i = 0; i < 1000 * 10; i++) {
+            arr = new byte[200];
+            Thread.sleep(1);
+        }
+        int rssLess = getRss();
+        System.out.println("Less rss: " + rssLess);
+        Asserts.assertTrue(rssLess < rssFull);
+        Asserts.assertTrue(Math.abs(rssFull - rssLess) > 350 * 1024);
+    }
+
+    private static OutputAnalyzer triggerJcmd(String arg1, String arg2, String arg3) throws Exception {
+        String pid = Integer.toString(ProcessTools.getProcessId());
+        JDKToolLauncher jcmd = JDKToolLauncher.create("jcmd")
+                                              .addToolArg(pid);
+        if (arg1 != null) {
+            jcmd.addToolArg(arg1);
+        }
+        if (arg2 != null) {
+            jcmd.addToolArg(arg2);
+        }
+        if (arg3 != null) {
+            jcmd.addToolArg(arg3);
+        }
+        ProcessBuilder pb = new ProcessBuilder(jcmd.getCommand());
+        return new OutputAnalyzer(pb.start());
+    }
+
+    private static int getRss() throws Exception {
+        String pid = Integer.toString(ProcessTools.getProcessId());
+        int rss = 0;
+        Process ps = Runtime.getRuntime().exec("cat /proc/"+pid+"/status");
+        ps.waitFor();
+        BufferedReader br = new BufferedReader(new InputStreamReader(ps.getInputStream()));
+        String line;
+        while (( line = br.readLine()) != null ) {
+            if (line.startsWith("VmRSS:") ) {
+                int numEnd = line.length() - 3;
+                int numBegin = line.lastIndexOf(" ", numEnd - 1) + 1;
+                rss = Integer.parseInt(line.substring(numBegin, numEnd));
+                break;
+            }
+        }
+        return rss;
+    }
+}

test/elastic-heap/TestElasticHeapJcmdError.java

+/*
+ * Copyright (c) 2019 Alibaba Group Holding Limited. All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Alibaba designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+import com.oracle.java.testlibrary.*;
+
+/* @test
+ * @summary test elastic-heap error with jcmd
+ * @library /testlibrary
+ * @build TestElasticHeapJcmdError
+ * @run main/othervm/timeout=100 TestElasticHeapJcmdError
+ */
+
+public class TestElasticHeapJcmdError {
+    public static void main(String[] args) throws Exception {
+        ProcessBuilder serverBuilder;
+
+        serverBuilder = ProcessTools.createJavaProcessBuilder("-XX:+UseG1GC",
+                "-Xmx1g", "-Xms1g",
+                "-Xmn100m", "-XX:G1HeapRegionSize=1m",
+                "-XX:ElasticHeapYGCIntervalMinMillis=50",
+                "-verbose:gc", "-XX:+PrintGCDetails", "-XX:+PrintGCTimeStamps",
+                "-Dtest.jdk=" + System.getProperty("test.jdk"),
+                Server.class.getName());
+        Process server = serverBuilder.start();
+
+        OutputAnalyzer output = new OutputAnalyzer(server);
+        System.out.println(output.getOutput());
+        output.shouldContain("Error: -XX:+G1ElasticHeap is not enabled");
+        Asserts.assertTrue(output.getExitValue() == 0);
+    }
+
+    private static class Server {
+        public static void main(String[] args) throws Exception {
+            byte[] arr = new byte[200*1024];
+            // Allocate 200k per 1ms, 200M per second
+            // so 2 GCs per second
+            for (int i = 0; i < 1000 * 5; i++) {
+                arr = new byte[200*1024];
+                Thread.sleep(1);
+            }
+            triggerJcmd("GC.elastic_heap", "young_commit_percent=50");
+            for (int i = 0; i < 1000 * 5; i++) {
+                arr = new byte[200*1024];
+                Thread.sleep(1);
+            }
+        }
+        private static void triggerJcmd(String arg1, String arg2) throws Exception {
+            String pid = Integer.toString(ProcessTools.getProcessId());
+            JDKToolLauncher jcmd = JDKToolLauncher.create("jcmd")
+                                                  .addToolArg(pid);
+            if (arg1 != null) {
+                jcmd.addToolArg(arg1);
+            }
+            if (arg2 != null) {
+                jcmd.addToolArg(arg2);
+            }
+            ProcessBuilder pb = new ProcessBuilder(jcmd.getCommand());
+            OutputAnalyzer output = new OutputAnalyzer(pb.start());
+            System.out.println(output.getOutput());
+            output.shouldHaveExitValue(0);
+        }
+    }
+}

test/elastic-heap/TestElasticHeapManyJcmds.java

+/*
+ * Copyright (c) 2019 Alibaba Group Holding Limited. All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Alibaba designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+import java.io.File;
+import com.oracle.java.testlibrary.*;
+
+/* @test
+ * @summary test elastic-heap with many jcmds
+ * @library /testlibrary
+ * @build TestElasticHeapManyJcmds
+ * @run main/othervm/timeout=300 TestElasticHeapManyJcmds
+ */
+
+class TestElasticHeapManyJcmdsSetter implements Runnable {
+    private int loopNum;
+    public TestElasticHeapManyJcmdsSetter(int ln) {
+        loopNum = ln;
+    }
+    private OutputAnalyzer triggerJcmd(String arg1, String arg2) throws Exception {
+        String pid = Integer.toString(ProcessTools.getProcessId());
+        JDKToolLauncher jcmd = JDKToolLauncher.create("jcmd")
+                                              .addToolArg(pid);
+        if (arg1 != null) {
+            jcmd.addToolArg(arg1);
+        }
+        if (arg2 != null) {
+            jcmd.addToolArg(arg2);
+        }
+        ProcessBuilder pb = new ProcessBuilder(jcmd.getCommand());
+        return new OutputAnalyzer(pb.start());
+    }
+    public void run() {
+        OutputAnalyzer output;
+        for (int i = 0; i < loopNum; i++) {
+            int p = 50 + i % 50;
+            try {
+                output = triggerJcmd("GC.elastic_heap", "young_commit_percent=" + p);
+                System.out.println(output.getOutput());
+            } catch (Exception e) {
+                System.out.println("Error: "+ e.getMessage());
+            }
+        }
+    }
+}
+
+public class TestElasticHeapManyJcmds {
+    public static void main(String[] args) throws Exception {
+        ProcessBuilder serverBuilder;
+
+        if (Platform.isDebugBuild()) {
+            serverBuilder = ProcessTools.createJavaProcessBuilder(
+                "-XX:+UseG1GC",
+                "-XX:+G1ElasticHeap", "-Xmx1g", "-Xms1g",
+                "-Xmn100m", "-XX:G1HeapRegionSize=1m",
+                "-XX:ElasticHeapYGCIntervalMinMillis=50",
+                "-verbose:gc", "-XX:+PrintGCDetails", "-XX:+PrintGCTimeStamps",
+                "-Dtest.jdk=" + System.getProperty("test.jdk"),
+                Server.class.getName(), "10");
+        } else {
+            serverBuilder = ProcessTools.createJavaProcessBuilder(
+                "-XX:+UseG1GC",
+                "-XX:+G1ElasticHeap", "-Xmx1g", "-Xms1g",
+                "-Xmn100m", "-XX:G1HeapRegionSize=1m",
+                "-XX:ElasticHeapYGCIntervalMinMillis=50",
+                "-verbose:gc", "-XX:+PrintGCDetails", "-XX:+PrintGCTimeStamps",
+                "-Dtest.jdk=" + System.getProperty("test.jdk"),
+                Server.class.getName(), "30");
+        }
+        Process server = serverBuilder.start();
+
+        OutputAnalyzer output = new OutputAnalyzer(server);
+        System.out.println(output.getOutput());
+        output.shouldContain("[GC.elastic_heap");
+        Asserts.assertTrue(output.getExitValue() == 0);
+    }
+
+    private static class Server {
+        public static void main(String[] args) throws Exception {
+            int loopNum = Integer.parseInt(args[0]);
+            byte[] arr = new byte[200*1024];
+            for (int i = 0; i < 1000 * 5; i++) {
+                arr = new byte[200*1024];
+                Thread.sleep(1);
+            }
+            TestElasticHeapManyJcmdsSetter setter = new TestElasticHeapManyJcmdsSetter(loopNum);
+            int count = Runtime.getRuntime().availableProcessors();
+            Thread[] t = new Thread[count];
+            for (int i = 0; i < count ; i++) {
+                t[i] = new Thread(setter, "t" + i);
+                t[i].start();
+            }
+            for (int i = 0; i < 1000 * 60; i++) {
+                arr = new byte[200*1024];
+                Thread.sleep(1);
+            }
+            System.exit(0);
+        }
+    }
+}

test/elastic-heap/TestElasticHeapMisc.java

+/*
+ * Copyright (c) 2019 Alibaba Group Holding Limited. All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Alibaba designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+import com.oracle.java.testlibrary.*;
+
+/* @test
+ * @summary test elastic-heap
+ * @library /testlibrary
+ * @build TestElasticHeapMisc
+ * @run main/othervm/timeout=100 TestElasticHeapMisc
+ */
+
+public class TestElasticHeapMisc {
+    public static void main(String[] args) throws Exception {
+        ProcessBuilder serverBuilder;
+
+        serverBuilder = ProcessTools.createJavaProcessBuilder("-XX:+UseG1GC",
+                "-XX:+G1ElasticHeap", "-Xmx1g", "-Xms1g",
+                "-Xmn100m", "-XX:G1HeapRegionSize=1m", "-XX:SurvivorRatio=1",
+                "-XX:ElasticHeapYGCIntervalMinMillis=50",
+                "-XX:InitiatingHeapOccupancyPercent=80",
+                "-verbose:gc", "-XX:+PrintGCDetails", "-XX:+PrintGCTimeStamps",
+                "-Dtest.jdk=" + System.getProperty("test.jdk"),
+                GenerationLimitLargerSurvivor.class.getName());
+        Process server = serverBuilder.start();
+
+        OutputAnalyzer output = new OutputAnalyzer(server);
+        System.out.println(output.getOutput());
+        // Will uncommit 70M in first time
+        output.shouldContain("[Elastic Heap concurrent thread: uncommit 71680K");
+        Asserts.assertTrue(output.getExitValue() == 0);
+
+        serverBuilder = ProcessTools.createJavaProcessBuilder("-XX:+UseG1GC",
+                "-XX:+G1ElasticHeap", "-Xmx1g", "-Xms1g",
+                "-Xmn100m", "-XX:G1HeapRegionSize=1m",
+                "-XX:ElasticHeapYGCIntervalMinMillis=50",
+                "-XX:ElasticHeapPeriodicYGCIntervalMillis=200",
+                "-XX:ElasticHeapPeriodicInitialMarkIntervalMillis=5000",
+                "-XX:InitiatingHeapOccupancyPercent=80",
+                "-verbose:gc", "-XX:+PrintGCDetails", "-XX:+PrintGCTimeStamps",
+                "-Dtest.jdk=" + System.getProperty("test.jdk"),
+                NoElasticHeapGC.class.getName());
+        server = serverBuilder.start();
+
+        output = new OutputAnalyzer(server);
+        System.out.println(output.getOutput());
+        output.shouldNotContain("Elastic Heap triggered GC");
+        Asserts.assertTrue(output.getExitValue() == 0);
+    }
+
+    private static class NoElasticHeapGC {
+        public static void main(String[] args) throws Exception {
+            byte[] arr;
+            for (int i = 0; i < 1000 * 15; i++) {
+                arr = new byte[20*1024];
+                Thread.sleep(1);
+            }
+        }
+    }
+
+    private static class GenerationLimitLargerSurvivor {
+        public static void main(String[] args) throws Exception {
+            Object[] root = new Object[1024*1024];
+            int rootIndex = 0;
+            byte[] arr = new byte[200*1024];
+            // Allocate 200k per 1ms , 200M per second
+            // so 2 GCs per second
+            // Make 10% survive
+            for (int i = 0; i < 1000 * 5; i++) {
+                if (i % 10 != 0) {
+                    arr = new byte[200*1024];
+                }
+                else {
+                    root[rootIndex++] = new byte[200*1024];
+                }
+                Thread.sleep(1);
+            }
+            triggerJcmd("GC.elastic_heap", "young_commit_percent=30");
+            for (int i = 0; i < 1000 * 7; i++) {
+                arr = new byte[200*1024];
+                Thread.sleep(1);
+            }
+        }
+        private static void triggerJcmd(String arg1, String arg2) throws Exception {
+            String pid = Integer.toString(ProcessTools.getProcessId());
+            JDKToolLauncher jcmd = JDKToolLauncher.create("jcmd")
+                                                  .addToolArg(pid);
+            if (arg1 != null) {
+                jcmd.addToolArg(arg1);
+            }
+            if (arg2 != null) {
+                jcmd.addToolArg(arg2);
+            }
+            ProcessBuilder pb = new ProcessBuilder(jcmd.getCommand());
+            OutputAnalyzer output = new OutputAnalyzer(pb.start());
+            System.out.println(output.getOutput());
+            output.shouldHaveExitValue(0);
+        }
+    }
+}

test/elastic-heap/TestElasticHeapPeriodic.java

+/*
+ * Copyright (c) 2019 Alibaba Group Holding Limited. All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Alibaba designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+import java.io.File;
+import com.oracle.java.testlibrary.*;
+
+/* @test
+ * @summary test elastic-heap periodic gc djust
+ * @library /testlibrary
+ * @build TestElasticHeapPeriodic
+ * @run main/othervm/timeout=600
+         -XX:+UseG1GC -XX:+G1ElasticHeap -Xmx1000m -Xms1000m
+                -XX:ElasticHeapPeriodicYGCIntervalMillis=400
+                -XX:ElasticHeapPeriodicUncommitStartupDelay=0
+                -Xmn200m -XX:G1HeapRegionSize=1m -XX:+AlwaysPreTouch
+                -XX:ElasticHeapYGCIntervalMinMillis=50
+                -verbose:gc -XX:+PrintGCDetails -XX:+PrintGCTimeStamps
+                TestElasticHeapPeriodic
+ */
+
+public class TestElasticHeapPeriodic {
+    public static void main(String[] args) throws Exception {
+        for (int i = 0; i < 3; i++) {
+            test();
+        }
+    }
+    public static void test() throws Exception {
+        OutputAnalyzer output;
+        byte[] arr = new byte[200*1024];
+        // Allocate 200k per 1ms , 200M per second
+        // so 2 GCs per second
+        for (int i = 0; i < 1000 * 3; i++) {
+            arr = new byte[200*1024];
+            Thread.sleep(1);
+        }
+        int rssFull = getRss();
+        System.out.println("rssFull: " + rssFull);
+        output = triggerJcmd("GC.elastic_heap", null);
+        System.out.println(output.getOutput());
+        output.shouldContain("[GC.elastic_heap: inactive]");
+        output.shouldHaveExitValue(0);
+
+        output = triggerJinfo("+ElasticHeapPeriodicUncommit");
+        output.shouldHaveExitValue(0);
+        output = triggerJinfo("ElasticHeapPeriodicMinYoungCommitPercent=50");
+        output.shouldHaveExitValue(0);
+        // Allocate 200k per ms , 200M per second
+        // so 1 GC per second
+        for (int i = 0; i < 1000 * 12; i++) {
+            arr = new byte[200*1024];
+            Thread.sleep(1);
+        }
+        int rss50 = getRss();
+        System.out.println("rss50: " + rss50);
+        output = triggerJcmd("GC.elastic_heap", null);
+        System.out.println(output.getOutput());
+        output.shouldContain("[GC.elastic_heap: young generation commit percent 50, uncommitted memory 104857600 B]");
+        output.shouldHaveExitValue(0);
+        System.gc();
+        Asserts.assertTrue(rss50 < rssFull);
+        Asserts.assertTrue(Math.abs(rssFull - rss50) > 80 * 1024);
+
+        // Allocate 1200k per ms, 1200M per second
+        // 6 GCs per second
+        for (int i = 0; i < 1000 * 10; i++) {
+            arr = new byte[400*1024];
+            arr = new byte[400*1024];
+            arr = new byte[400*1024];
+            Thread.sleep(1);
+        }
+        int rss100 = getRss();
+        System.out.println("rss100: " + rss100);
+        output = triggerJcmd("GC.elastic_heap", null);
+        System.out.println(output.getOutput());
+        output.shouldContain("[GC.elastic_heap: young generation commit percent 100, uncommitted memory 0 B]");
+        Asserts.assertTrue(rss50 < rssFull);
+        Asserts.assertTrue(Math.abs(rssFull - rss50) > 80 * 1024);
+        output.shouldHaveExitValue(0);
+
+        output = triggerJinfo("ElasticHeapPeriodicMinYoungCommitPercent=30");
+        output.shouldHaveExitValue(0);
+
+        // Allocate 100k per ms , 100M per second
+        // so 0.5 GC per second
+        for (int i = 0; i < 1000 * 22; i++) {
+            arr = new byte[100*1024];
+            Thread.sleep(1);
+        }
+
+        // Auto adjust happens
+        output = triggerJcmd("GC.elastic_heap", null);
+        System.out.println(output.getOutput());
+        output.shouldContain("[GC.elastic_heap: young generation commit percent 30, uncommitted memory 146800640 B]");
+        output.shouldHaveExitValue(0);
+        System.gc();
+        int rss30 = getRss();
+        System.out.println("rss30: " + rss30);
+        Asserts.assertTrue(rss30 < rss50);
+        Asserts.assertTrue(Math.abs(rssFull - rss30) > 120 * 1024);
+
+        output = triggerJinfo("ElasticHeapPeriodicMinYoungCommitPercent=70");
+        output.shouldHaveExitValue(0);
+        for (int i = 0; i < 1000 * 3; i++) {
+            arr = new byte[200*1024];
+            arr = new byte[200*1024];
+            arr = new byte[200*1024];
+            Thread.sleep(1);
+        }
+
+        // Allocate 200k per ms , 200M per second
+        // so 1 GC per second
+        for (int i = 0; i < 1000 * 12; i++) {
+            arr = new byte[200*1024];
+            Thread.sleep(1);
+        }
+        int rss70 = getRss();
+        System.out.println("rss70: " + rss70);
+        output = triggerJcmd("GC.elastic_heap", null);
+        System.out.println(output.getOutput());
+        output.shouldContain("[GC.elastic_heap: young generation commit percent 70, uncommitted memory 62914560 B]");
+        output.shouldHaveExitValue(0);
+        Asserts.assertTrue(rss70 < rssFull);
+        Asserts.assertTrue(rss70 > rss50);
+        Asserts.assertTrue(Math.abs(rssFull - rss70) > 40 * 1024);
+        output = triggerJinfo("-ElasticHeapPeriodicUncommit");
+        output.shouldHaveExitValue(0);
+        for (int i = 0; i < 1000 * 3; i++) {
+            arr = new byte[200*1024];
+            arr = new byte[200*1024];
+            arr = new byte[200*1024];
+            arr = new byte[200*1024];
+            arr = new byte[200*1024];
+            Thread.sleep(1);
+        }
+    }
+
+    private static OutputAnalyzer triggerJcmd(String arg1, String arg2) throws Exception {
+        String pid = Integer.toString(ProcessTools.getProcessId());
+        JDKToolLauncher jcmd = JDKToolLauncher.create("jcmd")
+                                              .addToolArg(pid);
+        if (arg1 != null) {
+            jcmd.addToolArg(arg1);
+        }
+        if (arg2 != null) {
+            jcmd.addToolArg(arg2);
+        }
+        ProcessBuilder pb = new ProcessBuilder(jcmd.getCommand());
+        return new OutputAnalyzer(pb.start());
+    }
+
+    private static OutputAnalyzer triggerJinfo(String arg) throws Exception {
+        String pid = Integer.toString(ProcessTools.getProcessId());
+        JDKToolLauncher jcmd = JDKToolLauncher.create("jinfo")
+                                              .addToolArg("-flag")
+                                              .addToolArg(arg)
+                                              .addToolArg(pid);
+        ProcessBuilder pb = new ProcessBuilder(jcmd.getCommand());
+        return new OutputAnalyzer(pb.start());
+    }
+    private static int getRss() throws Exception {
+        String pid = Integer.toString(ProcessTools.getProcessId());
+        int rss = 0;
+        Process ps = Runtime.getRuntime().exec("cat /proc/"+pid+"/status");
+        ps.waitFor();
+        BufferedReader br = new BufferedReader(new InputStreamReader(ps.getInputStream()));
+        String line;
+        while (( line = br.readLine()) != null ) {
+            if (line.startsWith("VmRSS:") ) {
+                int numEnd = line.length() - 3;
+                int numBegin = line.lastIndexOf(" ", numEnd - 1) + 1;
+                rss = Integer.parseInt(line.substring(numBegin, numEnd));
+                break;
+            }
+        }
+        return rss;
+    }
+}

test/elastic-heap/TestElasticHeapPeriodicHumAlloc.java

+/*
+ * Copyright (c) 2019 Alibaba Group Holding Limited. All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Alibaba designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+import com.oracle.java.testlibrary.*;
+
+/* @test
+ * @summary test elastic-heap periodic adjust with humongous allocation
+ * @library /testlibrary
+ * @build TestElasticHeapPeriodicHumAlloc
+ * @run main/othervm/timeout=300 TestElasticHeapPeriodicHumAlloc
+ */
+
+public class TestElasticHeapPeriodicHumAlloc {
+    public static void main(String[] args) throws Exception {
+        ProcessBuilder serverBuilder;
+
+        serverBuilder = ProcessTools.createJavaProcessBuilder(
+            "-XX:ElasticHeapPeriodicInitialMarkIntervalMillis=60000",
+            "-XX:ElasticHeapPeriodicMinYoungCommitPercent=10",
+            "-XX:+ElasticHeapPeriodicUncommit",
+            "-XX:ElasticHeapPeriodicUncommitStartupDelay=1",
+            "-XX:ElasticHeapPeriodicYGCIntervalMillis=5000",
+            "-XX:ElasticHeapYGCIntervalMinMillis=2000",
+            "-Xmx1g", "-Xms1g", "-XX:MaxNewSize=350m", "-XX:+PrintGC",
+            "-XX:+PrintGCDateStamps", "-XX:+PrintGCDetails", "-XX:+PrintGCTimeStamps",
+            "-XX:+UseG1GC", "-XX:+G1ElasticHeap",
+            Server.class.getName());
+        Process server = serverBuilder.start();
+
+        OutputAnalyzer output = new OutputAnalyzer(server);
+        System.out.println(output.getOutput());
+        output.shouldContain("G1 Humongous Allocation");
+        Asserts.assertTrue(output.getExitValue() == 0);
+    }
+
+    private static class Server {
+        public static void main(String[] args) throws Exception {
+            for (int i = 0; i < 2; i++) {
+                testloop();
+            }
+        }
+
+        public static void testloop() throws Exception {
+            Object[] root = new Object[40 * 1024];
+            for (int i = 0; i < 40 * 1024; i++) {
+                root[i] = new byte[10*1024];
+                if (i % 10 == 0) {
+                    Thread.sleep(1);
+                }
+            }
+
+            byte[] array;
+            for (int i = 0; i < 1000 * 20; i++) {
+                array = new byte[2*1024];
+                if ((i % 10)== 0) {
+                    array = new byte[600*1024];
+                }
+                Thread.sleep(1);
+            }
+            for (int i = 0; i < 1000 * 20; i++) {
+                array = new byte[100*1024];
+                array = new byte[100*1024];
+                array = new byte[100*1024];
+                if ((i % 10)== 0) {
+                    array = new byte[600*1024];
+                }
+                Thread.sleep(1);
+            }
+            root = null;
+            for (int i = 0; i < 1000 * 20; i++) {
+                array = new byte[2*1024];
+                if ((i % 10)== 0) {
+                    array = new byte[600*1024];
+                }
+                Thread.sleep(1);
+            }
+            for (int i = 0; i < 1000 * 20; i++) {
+                array = new byte[100*1024];
+                array = new byte[100*1024];
+                array = new byte[100*1024];
+                if ((i % 10)== 0) {
+                    array = new byte[600*1024];
+                }
+                Thread.sleep(1);
+            }
+        }
+    }
+}

test/elastic-heap/TestElasticHeapPeriodicInitialMark.java

+/*
+ * Copyright (c) 2019 Alibaba Group Holding Limited. All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Alibaba designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+import java.io.File;
+import com.oracle.java.testlibrary.*;
+
+/* @test
+ * @summary test elastic-heap periodic old gc uncommit with RSS check
+ * @library /testlibrary /testlibrary/whitebox
+ * @build TestElasticHeapPeriodicInitialMark
+ * @run main/othervm/timeout=200 TestElasticHeapPeriodicInitialMark
+ */
+
+public class TestElasticHeapPeriodicInitialMark {
+    public static void main(String[] args) throws Exception {
+        ProcessBuilder serverBuilder;
+        serverBuilder = ProcessTools.createJavaProcessBuilder("-XX:+UseG1GC",
+            "-XX:+G1ElasticHeap", "-XX:+ElasticHeapPeriodicUncommit",
+            "-XX:ElasticHeapPeriodicInitialMarkIntervalMillis=5000",
+            "-XX:ElasticHeapEagerMixedGCIntervalMillis=1000",
+            "-XX:ElasticHeapPeriodicMinYoungCommitPercent=100",
+            "-XX:ElasticHeapPeriodicUncommitStartupDelay=0",
+            "-Xmx1g", "-Xms1g", "-Xmn200m", "-XX:G1HeapRegionSize=1m",
+            "-XX:ElasticHeapYGCIntervalMinMillis=50",
+            "-XX:ElasticHeapInitialMarkIntervalMinMillis=0",
+            "-verbose:gc", "-XX:+PrintGCDetails", "-XX:+PrintGCTimeStamps",
+            "-XX:+PrintGCDateStamps",
+            "-Dtest.jdk=" + System.getProperty("test.jdk"),
+            Server.class.getName());
+        Process server = serverBuilder.start();
+        OutputAnalyzer output = new OutputAnalyzer(server);
+        System.out.println(output.getOutput());
+        Asserts.assertTrue(output.getExitValue() == 0);
+
+        serverBuilder = ProcessTools.createJavaProcessBuilder("-XX:+UseG1GC",
+            "-XX:+G1ElasticHeap", "-XX:+ElasticHeapPeriodicUncommit",
+            "-XX:ElasticHeapPeriodicInitialMarkIntervalMillis=5000",
+            "-XX:ElasticHeapPeriodicMinYoungCommitPercent=100",
+            "-XX:ElasticHeapPeriodicUncommitStartupDelay=0",
+            "-Xmx1g", "-Xms1g", "-Xmn200m", "-XX:G1HeapRegionSize=1m",
+            "-XX:ElasticHeapYGCIntervalMinMillis=50",
+            "-XX:ElasticHeapInitialMarkIntervalMinMillis=0",
+            "-verbose:gc", "-XX:+PrintGCDetails", "-XX:+PrintGCTimeStamps",
+            "-XX:+PrintGCDateStamps",
+            "-Dtest.jdk=" + System.getProperty("test.jdk"),
+            Server2.class.getName());
+        server = serverBuilder.start();
+        output = new OutputAnalyzer(server);
+        output.shouldContain("initial-mark");
+        output.shouldNotContain("(Elastic Heap triggered GC) (young),");
+        output.shouldMatch("(Elastic Heap triggered GC).*initial-mark");
+        System.out.println(output.getOutput());
+        Asserts.assertTrue(output.getExitValue() == 0);
+    }
+
+    private static class Server2 {
+        public static void main(String[] args) throws Exception {
+            byte[] arr = new byte[200*1024];
+            // Guaranteed gc will happen and mixed gc will finish
+            for (int i = 0; i < 1000 * 20; i++) {
+                arr = new byte[100 * 1024];
+                arr = new byte[100 * 1024];
+                Thread.sleep(1);
+            }
+        }
+    }
+
+    private static class Server {
+        public static void main(String[] args) throws Exception {
+            // Pretouch young gen
+            byte[] arr = new byte[200*1024];
+            for (int i = 0; i < 1000 * 5; i++) {
+                arr = new byte[200*1024];
+            }
+
+            // Promote 500M into old gen
+            Object[] root = new Object[5 * 1024];
+            for (int i = 0; i < 5 * 1024; i++) {
+                root[i] = new byte[100*1024];
+            }
+            System.gc();
+            root = null;
+            int fullRss = getRss();
+
+            // Guaranteed gc will happen and mixed gc will finish
+            for (int i = 0; i < 1000 * 15; i++) {
+                arr = new byte[2*1024];
+                Thread.sleep(1);
+            }
+            int lessRss = getRss();
+            Asserts.assertTrue((fullRss > lessRss) && (Math.abs(fullRss - lessRss) > 300 * 1024));
+        }
+
+        private static int getRss() throws Exception {
+            String pid = Integer.toString(ProcessTools.getProcessId());
+            int rss = 0;
+            Process ps = Runtime.getRuntime().exec("cat /proc/"+pid+"/status");
+            ps.waitFor();
+            BufferedReader br = new BufferedReader(new InputStreamReader(ps.getInputStream()));
+            String line;
+            while (( line = br.readLine()) != null ) {
+                if (line.startsWith("VmRSS:") ) {
+                    int numEnd = line.length() - 3;
+                    int numBegin = line.lastIndexOf(" ", numEnd - 1) + 1;
+                    rss = Integer.parseInt(line.substring(numBegin, numEnd));
+                    break;
+                }
+            }
+            return rss;
+        }
+    }
+}

test/elastic-heap/TestElasticHeapPeriodicOOM.java

+/*
+ * Copyright (c) 2019 Alibaba Group Holding Limited. All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Alibaba designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+import com.oracle.java.testlibrary.*;
+
+/* @test
+ * @summary test elastic-heap periodic adjust with OOM
+ * @library /testlibrary
+ * @build TestElasticHeapPeriodicOOM
+ * @run main/othervm/timeout=100 TestElasticHeapPeriodicOOM
+ */
+
+public class TestElasticHeapPeriodicOOM {
+    public static void main(String[] args) throws Exception {
+        ProcessBuilder serverBuilder;
+
+        serverBuilder = ProcessTools.createJavaProcessBuilder("-XX:+UseG1GC",
+                "-XX:+G1ElasticHeap", "-Xmx1g", "-Xms1g",
+                "-XX:+ElasticHeapPeriodicUncommit", "-XX:ElasticHeapPeriodicYGCIntervalMillis=50",
+                "-XX:ElasticHeapPeriodicUncommitStartupDelay=5",
+                "-Xmn100m", "-XX:G1HeapRegionSize=1m",
+                "-XX:ElasticHeapYGCIntervalMinMillis=10",
+                "-XX:ElasticHeapPeriodicMinYoungCommitPercent=30",
+                "-XX:InitiatingHeapOccupancyPercent=80",
+                "-verbose:gc", "-XX:+PrintGCDetails", "-XX:+PrintGCTimeStamps",
+                "-Dtest.jdk=" + System.getProperty("test.jdk"),
+                Server.class.getName());
+        Process server = serverBuilder.start();
+
+        OutputAnalyzer output = new OutputAnalyzer(server);
+        System.out.println(output.getOutput());
+        output.shouldContain("Elastic Heap concurrent thread: uncommit");
+        output.shouldContain("Elastic Heap recovers");
+        Asserts.assertTrue(output.getExitValue() != 0);
+    }
+
+    private static class Server {
+        public static void main(String[] args) throws Exception {
+            Object[] root = new Object[1024*1024];
+            int rootIndex = 0;
+            byte[] arr = new byte[200*1024];
+            // Allocate 200k per 1ms , 200M per second
+            // so 2 GCs per second
+            // Make 10% survive
+            for (int i = 0; i < 1000 * 10; i++) {
+                if (i % 10 != 0) {
+                    arr = new byte[200*1024];
+                }
+                else {
+                    root[rootIndex++] = new byte[200*1024];
+                }
+                Thread.sleep(1);
+            }
+            // Make 100M per second survive
+            for (int i = 0; i < 1000 * 10; i++) {
+                if (i % 2 != 0) {
+                    arr = new byte[200*1024];
+                }
+                else {
+                    root[rootIndex++] = new byte[200*1024];
+                }
+                Thread.sleep(1);
+            }
+        }
+    }
+}

test/elastic-heap/TestElasticHeapPeriodicYoung.java

+/*
+ * Copyright (c) 2019 Alibaba Group Holding Limited. All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Alibaba designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+import com.oracle.java.testlibrary.*;
+
+/* @test
+ * @summary test elastic-heap periodic adjust young gen
+ * @library /testlibrary
+ * @build TestElasticHeapPeriodicYoung
+ * @run main/othervm/timeout=200 TestElasticHeapPeriodicYoung
+ */
+
+public class TestElasticHeapPeriodicYoung {
+    public static void main(String[] args) throws Exception {
+        ProcessBuilder serverBuilder;
+
+        serverBuilder = ProcessTools.createJavaProcessBuilder("-XX:+UseG1GC",
+                "-XX:+G1ElasticHeap", "-Xmx1g", "-Xms1g",
+                "-XX:+ElasticHeapPeriodicUncommit", "-XX:ElasticHeapPeriodicYGCIntervalMillis=150",
+                "-XX:ElasticHeapPeriodicUncommitStartupDelay=5",
+                "-Xmn100m", "-XX:G1HeapRegionSize=1m", "-XX:SurvivorRatio=1",
+                "-XX:ElasticHeapYGCIntervalMinMillis=10",
+                "-XX:ElasticHeapPeriodicMinYoungCommitPercent=40",
+                "-XX:InitiatingHeapOccupancyPercent=80",
+                "-verbose:gc", "-XX:+PrintGCDetails", "-XX:+PrintGCTimeStamps",
+                "-Dtest.jdk=" + System.getProperty("test.jdk"),
+                Server.class.getName());
+        Process server = serverBuilder.start();
+
+        OutputAnalyzer output = new OutputAnalyzer(server);
+        System.out.println(output.getOutput());
+        // Will not deallocate 60M in first time because of 50M survivor size
+        String s = output.firstMatch("Elastic Heap concurrent thread: uncommit \\d+");
+        Asserts.assertTrue(s != null);
+        Asserts.assertFalse("Elastic Heap concurrent thread: uncommit 60".equals(s));
+        Asserts.assertTrue(output.getExitValue() == 0);
+
+        serverBuilder = ProcessTools.createJavaProcessBuilder("-XX:+UseG1GC",
+                "-XX:+G1ElasticHeap", "-Xmx1g", "-Xms1g",
+                "-XX:+ElasticHeapPeriodicUncommit", "-XX:ElasticHeapPeriodicYGCIntervalMillis=500",
+                "-XX:ElasticHeapPeriodicUncommitStartupDelay=1",
+                "-Xmn100m", "-XX:G1HeapRegionSize=1m",
+                "-XX:ElasticHeapYGCIntervalMinMillis=10",
+                "-XX:ElasticHeapPeriodicMinYoungCommitPercent=40",
+                "-XX:InitiatingHeapOccupancyPercent=80",
+                "-verbose:gc", "-XX:+PrintGCDetails", "-XX:+PrintGCTimeStamps",
+                "-Dtest.jdk=" + System.getProperty("test.jdk"),
+                Server2.class.getName());
+        server = serverBuilder.start();
+
+        output = new OutputAnalyzer(server);
+        System.out.println(output.getOutput());
+        output.shouldContain("Elastic Heap concurrent thread: uncommit");
+        Asserts.assertTrue(output.getExitValue() == 0);
+    }
+
+    private static class Server2 {
+        public static void main(String[] args) throws Exception {
+            byte[] arr = new byte[200*1024];
+            for (int i = 0; i < 1000 * 4; i++) {
+                arr = new byte[200*1024];
+                Thread.sleep(1);
+            }
+            for (int i = 0; i < 1000 * 20; i++) {
+                Thread.sleep(1);
+            }
+        }
+    }
+
+    private static class Server {
+        public static void main(String[] args) throws Exception {
+            Object[] root = new Object[1024*1024];
+            int rootIndex = 0;
+            byte[] arr = new byte[200*1024];
+            // Allocate 200k per 1ms , 200M per second
+            // so 2 GCs per second
+            // Make 10% survive
+            for (int i = 0; i < 1000 * 12; i++) {
+                if (i % 10 != 0) {
+                    arr = new byte[200*1024];
+                }
+                else {
+                    root[rootIndex++] = new byte[200*1024];
+                }
+                Thread.sleep(1);
+            }
+        }
+    }
+}

test/elastic-heap/TestElasticHeapSoftmxPercent.java

+/*
+ * Copyright (c) 2019 Alibaba Group Holding Limited. All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Alibaba designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+import java.io.File;
+import com.oracle.java.testlibrary.*;
+
+/* @test
+ * @summary test elastic-heap setting softmx percent with RSS check
+ * @library /testlibrary /testlibrary/whitebox
+ * @build TestElasticHeapSoftmxPercent
+ * @run main/othervm/timeout=200 TestElasticHeapSoftmxPercent
+ */
+
+public class TestElasticHeapSoftmxPercent {
+    public static void main(String[] args) throws Exception {
+        ProcessBuilder serverBuilder;
+        serverBuilder = ProcessTools.createJavaProcessBuilder("-XX:+UseG1GC",
+            "-XX:+G1ElasticHeap",
+            "-Xmx1000m", "-Xms1000m", "-XX:G1HeapRegionSize=1m", "-XX:+AlwaysPreTouch",
+            "-verbose:gc", "-XX:+PrintGCDetails", "-XX:+PrintGCTimeStamps",
+            "-Dtest.jdk=" + System.getProperty("test.jdk"),
+            Server.class.getName());
+        Process server = serverBuilder.start();
+        OutputAnalyzer output = new OutputAnalyzer(server);
+        System.out.println(output.getOutput());
+        // Should not have regular initial-mark
+        output.shouldNotContain("[GC pause (G1 Evacuation Pause) (young) (initial-mark)");
+        Asserts.assertTrue(output.getExitValue() == 0);
+    }
+
+    private static class Server {
+        public static void main(String[] args) throws Exception {
+            // Promote 400M into old gen
+            Object[] root = new Object[4 * 1024];
+            for (int i = 0; i < 4 * 1024; i++) {
+                root[i] = new byte[100*1024];
+            }
+
+            byte[] arr = new byte[200*1024];
+            // Allocate 200k per 1ms, 200M per second
+            for (int i = 0; i < 1000 * 10; i++) {
+                arr = new byte[200*1024];
+                Thread.sleep(1);
+            }
+
+            System.gc();
+            int fullRss = getRss();
+            System.out.println("Full rss: " + fullRss);
+            Asserts.assertTrue(fullRss > 1000 * 1024);
+            OutputAnalyzer output = triggerJcmd("GC.elastic_heap", "softmx_percent=50");
+            System.out.println(output.getOutput());
+
+            // Allocate 400k per 1ms, 400M per second
+            for (int i = 0; i < 1000 * 10; i++) {
+                arr = new byte[400*1024];
+                Thread.sleep(1);
+            }
+            output = triggerJcmd("GC.elastic_heap", null);
+            System.out.println(output.getOutput());
+            output.shouldContain("[GC.elastic_heap: inactive]");
+
+            output = triggerJcmd("GC.elastic_heap", "softmx_percent=60");
+            System.out.println(output.getOutput());
+            // Allocate 400k per 1ms, 400M per second
+            for (int i = 0; i < 1000 * 10; i++) {
+                arr = new byte[400*1024];
+                Thread.sleep(1);
+            }
+
+            output = triggerJcmd("GC.elastic_heap", null);
+            System.out.println(output.getOutput());
+            output.shouldContain("[GC.elastic_heap: in softmx mode]");
+            output.shouldContain("[GC.elastic_heap: softmx percent 60, uncommitted memory 419430400 B]");
+            int rss60 = getRss();
+            System.out.println("60% rss: " + rss60);
+            Asserts.assertTrue(Math.abs(fullRss - rss60) > 350 * 1024);
+
+            System.gc();
+
+            output = triggerJcmd("GC.elastic_heap", "softmx_percent=80");
+            System.out.println(output.getOutput());
+            // Allocate 400k per 1ms, 400M per second
+            for (int i = 0; i < 1000 * 10; i++) {
+                arr = new byte[400*1024];
+                Thread.sleep(1);
+            }
+
+            output = triggerJcmd("GC.elastic_heap", null);
+            System.out.println(output.getOutput());
+            output.shouldContain("[GC.elastic_heap: in softmx mode]");
+            output.shouldContain("[GC.elastic_heap: softmx percent 80, uncommitted memory 209715200 B]");
+            int rss80 = getRss();
+            System.out.println("80% rss: " + rss80);
+            Asserts.assertTrue(Math.abs(fullRss - rss80) > 150 * 1024);
+            Asserts.assertTrue(Math.abs(rss80 - rss60) > 150 * 1024);
+
+            output = triggerJcmd("GC.elastic_heap", "softmx_percent=0");
+            System.out.println(output.getOutput());
+            // Allocate 400k per 1ms, 400M per second
+            for (int i = 0; i < 1000 * 10; i++) {
+                arr = new byte[400*1024];
+                Thread.sleep(1);
+            }
+
+            output = triggerJcmd("GC.elastic_heap", null);
+            System.out.println(output.getOutput());
+            output.shouldContain("[GC.elastic_heap: inactive]");
+            int rss100 = getRss();
+            System.out.println("100% rss: " + rss100);
+            Asserts.assertTrue(Math.abs(fullRss - rss100) < 100 * 1024);
+
+            output = triggerJcmd("GC.elastic_heap", "softmx_percent=70");
+            System.out.println(output.getOutput());
+            // Allocate 400k per 1ms, 400M per second
+            for (int i = 0; i < 1000 * 10; i++) {
+                arr = new byte[400*1024];
+                Thread.sleep(1);
+            }
+            System.gc();
+
+            output = triggerJcmd("GC.elastic_heap", null);
+            System.out.println(output.getOutput());
+            output.shouldContain("[GC.elastic_heap: in softmx mode]");
+            output.shouldContain("[GC.elastic_heap: softmx percent 70, uncommitted memory 314572800 B]");
+            int rss70 = getRss();
+            System.out.println("70% rss: " + rss70);
+            Asserts.assertTrue(Math.abs(fullRss - rss70) > 250 * 1024);
+        }
+
+        private static OutputAnalyzer triggerJcmd(String arg1, String arg2) throws Exception {
+            String pid = Integer.toString(ProcessTools.getProcessId());
+            JDKToolLauncher jcmd = JDKToolLauncher.create("jcmd")
+                                                  .addToolArg(pid);
+            if (arg1 != null) {
+                jcmd.addToolArg(arg1);
+            }
+            if (arg2 != null) {
+                jcmd.addToolArg(arg2);
+            }
+            ProcessBuilder pb = new ProcessBuilder(jcmd.getCommand());
+            return new OutputAnalyzer(pb.start());
+        }
+
+        private static int getRss() throws Exception {
+            String pid = Integer.toString(ProcessTools.getProcessId());
+            int rss = 0;
+            Process ps = Runtime.getRuntime().exec("cat /proc/"+pid+"/status");
+            ps.waitFor();
+            BufferedReader br = new BufferedReader(new InputStreamReader(ps.getInputStream()));
+            String line;
+            while (( line = br.readLine()) != null ) {
+                if (line.startsWith("VmRSS:") ) {
+                    int numEnd = line.length() - 3;
+                    int numBegin = line.lastIndexOf(" ", numEnd - 1) + 1;
+                    rss = Integer.parseInt(line.substring(numBegin, numEnd));
+                    break;
+                }
+            }
+            return rss;
+        }
+    }
+}

test/elastic-heap/TestElasticHeapSoftmxPercentFail.java

+/*
+ * Copyright (c) 2019 Alibaba Group Holding Limited. All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Alibaba designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+import java.io.File;
+import com.oracle.java.testlibrary.*;
+
+/* @test
+ * @summary test elastic-heap setting heap commit percent fail
+ * @library /testlibrary /testlibrary/whitebox
+ * @build TestElasticHeapSoftmxPercentFail
+ * @run main/othervm/timeout=200 TestElasticHeapSoftmxPercentFail
+ */
+
+public class TestElasticHeapSoftmxPercentFail {
+    public static void main(String[] args) throws Exception {
+        ProcessBuilder serverBuilder;
+        Process server;
+        OutputAnalyzer output;
+        serverBuilder = ProcessTools.createJavaProcessBuilder("-XX:+UseG1GC",
+            "-XX:+G1ElasticHeap",
+            "-Xmx1000m", "-Xms1000m", "-XX:G1HeapRegionSize=1m", "-XX:+AlwaysPreTouch",
+            "-verbose:gc", "-XX:+PrintGCDetails", "-XX:+PrintGCTimeStamps",
+            "-Dtest.jdk=" + System.getProperty("test.jdk"),
+            Server.class.getName());
+        server = serverBuilder.start();
+        output = new OutputAnalyzer(server);
+        System.out.println(output.getOutput());
+        output.shouldContain("softmx percent setting failed");
+        Asserts.assertTrue(output.getExitValue() == 0);
+
+        serverBuilder = ProcessTools.createJavaProcessBuilder("-XX:+UseG1GC",
+            "-XX:+G1ElasticHeap",
+            "-Xmx600m", "-Xms600m", "-XX:G1HeapRegionSize=1m", "-XX:+AlwaysPreTouch",
+            "-Xmn300m",
+            "-verbose:gc", "-XX:+PrintGCDetails", "-XX:+PrintGCTimeStamps",
+            "-Dtest.jdk=" + System.getProperty("test.jdk"),
+            Server2.class.getName());
+        server = serverBuilder.start();
+        output = new OutputAnalyzer(server);
+        System.out.println(output.getOutput());
+        output.shouldContain("to-space exhausted");
+        Asserts.assertTrue(output.getExitValue() == 0);
+
+        serverBuilder = ProcessTools.createJavaProcessBuilder("-XX:+UseG1GC",
+            "-XX:+G1ElasticHeap",
+            "-Xmx1000m", "-Xms1000m", "-XX:G1HeapRegionSize=1m", "-XX:+AlwaysPreTouch",
+            "-Xmn300m",
+            "-verbose:gc", "-XX:+PrintGCDetails", "-XX:+PrintGCTimeStamps",
+            "-Dtest.jdk=" + System.getProperty("test.jdk"),
+            Server3.class.getName());
+        server = serverBuilder.start();
+        output = new OutputAnalyzer(server);
+        System.out.println(output.getOutput());
+        output.shouldNotContain("to-space exhausted");
+        output.shouldNotContain("softmx percent setting failed");
+        Asserts.assertTrue(output.getExitValue() == 0);
+
+        serverBuilder = ProcessTools.createJavaProcessBuilder("-XX:+UseG1GC",
+            "-XX:+G1ElasticHeap",
+            "-Xmx1000m", "-Xms1000m", "-XX:G1HeapRegionSize=1m", "-XX:+AlwaysPreTouch",
+            "-Xmn200m",
+            "-verbose:gc", "-XX:+PrintGCDetails", "-XX:+PrintGCTimeStamps",
+            "-Dtest.jdk=" + System.getProperty("test.jdk"),
+            Server4.class.getName());
+        server = serverBuilder.start();
+        output = new OutputAnalyzer(server);
+        System.out.println(output.getOutput());
+        output.shouldContain("Eden: 101376.0K");
+        output.shouldNotContain("softmx percent setting failed");
+        Asserts.assertTrue(output.getExitValue() == 0);
+
+        serverBuilder = ProcessTools.createJavaProcessBuilder("-XX:+UseG1GC",
+            "-XX:+G1ElasticHeap",
+            "-Xmx1000m", "-Xms500m", "-XX:G1HeapRegionSize=1m", "-XX:+AlwaysPreTouch",
+            "-Xmn200m",
+            "-verbose:gc", "-XX:+PrintGCDetails", "-XX:+PrintGCTimeStamps",
+            "-Dtest.jdk=" + System.getProperty("test.jdk"),
+            Server4.class.getName());
+        server = serverBuilder.start();
+        output = new OutputAnalyzer(server);
+        System.out.println(output.getOutput());
+        output.shouldContain("same to Xmx");
+        Asserts.assertTrue(output.getExitValue() != 0);
+
+    }
+
+    private static class Server {
+        public static void main(String[] args) throws Exception {
+            // Promote 400M into old gen
+            Object[] root = new Object[4 * 1024];
+            for (int i = 0; i < 4 * 1024; i++) {
+                root[i] = new byte[99*1024];
+            }
+
+            byte[] arr = new byte[200*1024];
+            // Allocate 200k per 1ms, 200M per second
+            for (int i = 0; i < 1000 * 10; i++) {
+                arr = new byte[200*1024];
+                Thread.sleep(1);
+            }
+
+            OutputAnalyzer output = triggerJcmd("GC.elastic_heap", "softmx_percent=50");
+            System.out.println(output.getOutput());
+            // Allocate 200k per 1ms, 200M per second
+            for (int i = 0; i < 1000 * 10; i++) {
+                arr = new byte[200*1024];
+                Thread.sleep(1);
+            }
+        }
+
+        private static OutputAnalyzer triggerJcmd(String arg1, String arg2) throws Exception {
+            String pid = Integer.toString(ProcessTools.getProcessId());
+            JDKToolLauncher jcmd = JDKToolLauncher.create("jcmd")
+                                                  .addToolArg(pid);
+            if (arg1 != null) {
+                jcmd.addToolArg(arg1);
+            }
+            if (arg2 != null) {
+                jcmd.addToolArg(arg2);
+            }
+            ProcessBuilder pb = new ProcessBuilder(jcmd.getCommand());
+            return new OutputAnalyzer(pb.start());
+        }
+    }
+    private static class Server2 extends Server {
+        public static void main(String[] args) throws Exception {
+            // Promote 400M into old gen
+            Object[] root = new Object[4 * 1024];
+            for (int i = 0; i < 4 * 1024; i++) {
+                root[i] = new byte[99*1024];
+            }
+
+            byte[] arr = new byte[200*1024];
+            for (int i = 0; i < 1000 * 10; i++) {
+                arr = new byte[200*1024];
+                arr = new byte[200*1024];
+                Thread.sleep(1);
+            }
+        }
+    }
+
+    private static class Server3 extends Server {
+        public static void main(String[] args) throws Exception {
+            // Promote 400M into old gen
+            Object[] root = new Object[4 * 1024];
+            for (int i = 0; i < 4 * 1024; i++) {
+                root[i] = new byte[99*1024];
+            }
+
+            byte[] arr = new byte[200*1024];
+            // Allocate 200k per 1ms, 200M per second
+            for (int i = 0; i < 1000 * 10; i++) {
+                arr = new byte[200*1024];
+                arr = new byte[200*1024];
+                Thread.sleep(1);
+            }
+
+            OutputAnalyzer output = Server.triggerJcmd("GC.elastic_heap", "softmx_percent=60");
+            System.out.println(output.getOutput());
+            // Allocate 200k per 1ms, 200M per second
+            for (int i = 0; i < 1000 * 10; i++) {
+                arr = new byte[200*1024];
+                arr = new byte[200*1024];
+                Thread.sleep(1);
+            }
+        }
+    }
+
+    private static class Server4 extends Server {
+        public static void main(String[] args) throws Exception {
+            // Promote 200M into old gen
+            Object[] root = new Object[2 * 1024];
+            for (int i = 0; i < 2 * 1024; i++) {
+                root[i] = new byte[99*1024];
+            }
+
+            byte[] arr = new byte[200*1024];
+            // Allocate 200k per 1ms, 200M per second
+            for (int i = 0; i < 1000 * 10; i++) {
+                arr = new byte[200*1024];
+                arr = new byte[200*1024];
+                Thread.sleep(1);
+            }
+
+            OutputAnalyzer output = Server.triggerJcmd("GC.elastic_heap", "softmx_percent=50");
+            System.out.println(output.getOutput());
+            // Allocate 200k per 1ms, 200M per second
+            for (int i = 0; i < 1000 * 10; i++) {
+                arr = new byte[200*1024];
+                arr = new byte[200*1024];
+                Thread.sleep(1);
+            }
+        }
+    }
+}

test/elastic-heap/TestElasticHeapYoungOldGenOverlap.java

+/*
+ * Copyright (c) 2019 Alibaba Group Holding Limited. All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Alibaba designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+import java.io.File;
+import com.oracle.java.testlibrary.*;
+
+/* @test
+ * @summary test elastic-heap with young-gen old-gen overlap
+ * @library /testlibrary
+ * @build TestElasticHeapYoungOldGenOverlap
+ * @run main/othervm/timeout=200 TestElasticHeapYoungOldGenOverlap
+ */
+
+public class TestElasticHeapYoungOldGenOverlap {
+    public static void main(String[] args) throws Exception {
+        ProcessBuilder serverBuilder;
+        Process server;
+        OutputAnalyzer output;
+
+        serverBuilder = ProcessTools.createJavaProcessBuilder("-XX:+UseG1GC",
+                "-XX:+G1ElasticHeap", "-Xmx1000m", "-Xms1000m",
+                "-XX:+ElasticHeapPeriodicUncommit",
+                "-XX:ElasticHeapPeriodicYGCIntervalMillis=400",
+                "-XX:ElasticHeapPeriodicUncommitStartupDelay=0",
+                "-XX:MaxNewSize=400m", "-XX:G1HeapRegionSize=1m", "-XX:+AlwaysPreTouch",
+                "-XX:InitiatingHeapOccupancyPercent=90",
+                "-XX:ElasticHeapYGCIntervalMinMillis=100",
+                "-verbose:gc", "-XX:+PrintGCDetails", "-XX:+PrintGCTimeStamps",
+                "-Dtest.jdk=" + System.getProperty("test.jdk"),
+                Server.class.getName());
+        server = serverBuilder.start();
+
+        output = new OutputAnalyzer(server);
+        System.out.println(output.getOutput());
+        output.shouldContain("Elastic Heap concurrent thread: commit");
+        output.shouldNotContain("Full GC");
+        Asserts.assertTrue(output.getExitValue() == 0);
+
+        serverBuilder = ProcessTools.createJavaProcessBuilder("-XX:+UseG1GC",
+                "-XX:+G1ElasticHeap", "-Xmx1000m", "-Xms1000m",
+                "-XX:ElasticHeapPeriodicYGCIntervalMillis=400",
+                "-XX:ElasticHeapPeriodicUncommitStartupDelay=0",
+                "-XX:MaxNewSize=400m", "-XX:G1HeapRegionSize=1m", "-XX:+AlwaysPreTouch",
+                "-XX:InitiatingHeapOccupancyPercent=90",
+                "-XX:ElasticHeapYGCIntervalMinMillis=50",
+                "-verbose:gc", "-XX:+PrintGCDetails", "-XX:+PrintGCTimeStamps",
+                "-Dtest.jdk=" + System.getProperty("test.jdk"),
+                Server2.class.getName());
+        server = serverBuilder.start();
+        output = new OutputAnalyzer(server);
+        System.out.println(output.getOutput());
+        Asserts.assertTrue(output.getExitValue() == 0);
+
+        serverBuilder = ProcessTools.createJavaProcessBuilder("-XX:+UseG1GC",
+                "-XX:+G1ElasticHeap", "-Xmx1000m", "-Xms1000m",
+                "-XX:ElasticHeapPeriodicYGCIntervalMillis=400",
+                "-XX:ElasticHeapPeriodicUncommitStartupDelay=0",
+                "-XX:MaxNewSize=400m", "-XX:G1HeapRegionSize=1m", "-XX:+AlwaysPreTouch",
+                "-XX:InitiatingHeapOccupancyPercent=50",
+                "-XX:ElasticHeapYGCIntervalMinMillis=50",
+                "-verbose:gc", "-XX:+PrintGCDetails", "-XX:+PrintGCTimeStamps",
+                "-Dtest.jdk=" + System.getProperty("test.jdk"),
+                Server3.class.getName());
+        server = serverBuilder.start();
+        output = new OutputAnalyzer(server);
+        System.out.println(output.getOutput());
+        Asserts.assertTrue(output.getExitValue() == 0);
+    }
+
+    private static class Server {
+        public static void main(String[] args) throws Exception {
+            OutputAnalyzer output;
+            byte[] arr = new byte[200*1024];
+            // Allocate 400k per 1ms , 400M per second
+            // so 1 GC per second
+            for (int i = 0; i < 1000 * 15; i++) {
+                arr = new byte[200*1024];
+                arr = new byte[200*1024];
+                Thread.sleep(1);
+            }
+            output = triggerJcmd("GC.elastic_heap", null);
+            System.out.println(output.getOutput());
+            output.shouldContain("[GC.elastic_heap: young generation commit percent 50, uncommitted memory 209715200 B]");
+            output.shouldHaveExitValue(0);
+
+            // Promote 800m to old gen
+            Object[] root = new Object[8000];
+            for (int i = 0; i < 8000; i += 4) {
+                root[i] = new byte[100*1024];
+                root[i+1] = new byte[100*1024];
+                root[i+2] = new byte[100*1024];
+                root[i+3] = new byte[100*1024];
+                Thread.sleep(1);
+            }
+            for (int i = 0; i < 1000 * 1; i++) {
+                arr = new byte[200*1024];
+                arr = new byte[200*1024];
+                Thread.sleep(1);
+            }
+
+            output = triggerJcmd("GC.elastic_heap", null);
+            System.out.println(output.getOutput());
+            output.shouldContain("[GC.elastic_heap: young generation commit percent 100, uncommitted memory 0 B]");
+            output.shouldHaveExitValue(0);
+
+        }
+
+        private static OutputAnalyzer triggerJcmd(String arg1, String arg2) throws Exception {
+            String pid = Integer.toString(ProcessTools.getProcessId());
+            JDKToolLauncher jcmd = JDKToolLauncher.create("jcmd")
+                                                  .addToolArg(pid);
+            if (arg1 != null) {
+                jcmd.addToolArg(arg1);
+            }
+            if (arg2 != null) {
+                jcmd.addToolArg(arg2);
+            }
+            ProcessBuilder pb = new ProcessBuilder(jcmd.getCommand());
+            return new OutputAnalyzer(pb.start());
+        }
+
+        private static OutputAnalyzer triggerJinfo(String arg) throws Exception {
+            String pid = Integer.toString(ProcessTools.getProcessId());
+            JDKToolLauncher jcmd = JDKToolLauncher.create("jinfo")
+                                                  .addToolArg("-flag")
+                                                  .addToolArg(arg)
+                                                  .addToolArg(pid);
+            ProcessBuilder pb = new ProcessBuilder(jcmd.getCommand());
+            return new OutputAnalyzer(pb.start());
+        }
+        private static int getRss() throws Exception {
+            String pid = Integer.toString(ProcessTools.getProcessId());
+            int rss = 0;
+            Process ps = Runtime.getRuntime().exec("cat /proc/"+pid+"/status");
+            ps.waitFor();
+            BufferedReader br = new BufferedReader(new InputStreamReader(ps.getInputStream()));
+            String line;
+            while (( line = br.readLine()) != null ) {
+                if (line.startsWith("VmRSS:") ) {
+                    int numEnd = line.length() - 3;
+                    int numBegin = line.lastIndexOf(" ", numEnd - 1) + 1;
+                    rss = Integer.parseInt(line.substring(numBegin, numEnd));
+                    break;
+                }
+            }
+            return rss;
+        }
+    }
+
+    private static class Server2 extends Server {
+        public static void main(String[] args) throws Exception {
+            OutputAnalyzer output;
+            byte[] arr = new byte[200*1024];
+            // Allocate 400k per 1ms , 400M per second
+            // so 1 GC per second
+            for (int i = 0; i < 1000 * 15; i++) {
+                arr = new byte[200*1024];
+                arr = new byte[200*1024];
+                Thread.sleep(1);
+            }
+            output = Server.triggerJcmd("GC.elastic_heap", "young_commit_percent=20");
+            System.out.println(output.getOutput());
+            output.shouldContain("Error: command fails");
+            output.shouldHaveExitValue(0);
+        }
+    }
+    private static class Server3 extends Server {
+        public static void main(String[] args) throws Exception {
+            OutputAnalyzer output;
+            byte[] arr = new byte[200*1024];
+            // Allocate 100k per 1ms , 100M per second
+            for (int i = 0; i < 1000 * 15; i++) {
+                arr = new byte[100*1024];
+                Thread.sleep(1);
+            }
+            output = Server.triggerJcmd("GC.elastic_heap", "young_commit_percent=20");
+            System.out.println(output.getOutput());
+            output.shouldContain("[GC.elastic_heap: young generation commit percent 20");
+            output.shouldHaveExitValue(0);
+        }
+    }
+
+}