7172388: G1: _total_full_collections should not be incremented for concurrent cycles

Reviewed-by: azeemj, jmasa

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

@@ -293,7 +293,7 @@ void ConcurrentMarkThread::run() {
     // Java thread is waiting for a full GC to happen (e.g., it
     // called System.gc() with +ExplicitGCInvokesConcurrent).
     _sts.join();
-    g1h->increment_full_collections_completed(true /* concurrent */);
+    g1h->increment_old_marking_cycles_completed(true /* concurrent */);
     _sts.leave();
   }
   assert(_should_terminate, "just checking");

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

@@ -1299,6 +1299,7 @@ bool G1CollectedHeap::do_collection(bool explicit_gc,
 
     gc_prologue(true);
     increment_total_collections(true /* full gc */);
+    increment_old_marking_cycles_started();
 
     size_t g1h_prev_used = used();
     assert(used() == recalculate_used(), "Should be equal");
@@ -1501,7 +1502,7 @@ bool G1CollectedHeap::do_collection(bool explicit_gc,
     "young list should be empty at this point");
 
   // Update the number of full collections that have been completed.
-  increment_full_collections_completed(false /* concurrent */);
+  increment_old_marking_cycles_completed(false /* concurrent */);
 
   _hrs.verify_optional();
   verify_region_sets_optional();
@@ -1888,7 +1889,8 @@ G1CollectedHeap::G1CollectedHeap(G1CollectorPolicy* policy_) :
   _retained_old_gc_alloc_region(NULL),
   _expand_heap_after_alloc_failure(true),
   _surviving_young_words(NULL),
-  _full_collections_completed(0),
+  _old_marking_cycles_started(0),
+  _old_marking_cycles_completed(0),
   _in_cset_fast_test(NULL),
   _in_cset_fast_test_base(NULL),
   _dirty_cards_region_list(NULL),
@@ -2360,7 +2362,16 @@ void G1CollectedHeap::allocate_dummy_regions() {
 }
 #endif // !PRODUCT
 
-void G1CollectedHeap::increment_full_collections_completed(bool concurrent) {
+void G1CollectedHeap::increment_old_marking_cycles_started() {
+  assert(_old_marking_cycles_started == _old_marking_cycles_completed ||
+    _old_marking_cycles_started == _old_marking_cycles_completed + 1,
+    err_msg("Wrong marking cycle count (started: %d, completed: %d)",
+    _old_marking_cycles_started, _old_marking_cycles_completed));
+
+  _old_marking_cycles_started++;
+}
+
+void G1CollectedHeap::increment_old_marking_cycles_completed(bool concurrent) {
   MonitorLockerEx x(FullGCCount_lock, Mutex::_no_safepoint_check_flag);
 
   // We assume that if concurrent == true, then the caller is a
@@ -2368,11 +2379,6 @@ void G1CollectedHeap::increment_full_collections_completed(bool concurrent) {
   // Set. If there's ever a cheap way to check this, we should add an
   // assert here.
 
-  // We have already incremented _total_full_collections at the start
-  // of the GC, so total_full_collections() represents how many full
-  // collections have been started.
-  unsigned int full_collections_started = total_full_collections();
-
   // Given that this method is called at the end of a Full GC or of a
   // concurrent cycle, and those can be nested (i.e., a Full GC can
   // interrupt a concurrent cycle), the number of full collections
@@ -2382,21 +2388,21 @@ void G1CollectedHeap::increment_full_collections_completed(bool concurrent) {
 
   // This is the case for the inner caller, i.e. a Full GC.
   assert(concurrent ||
-         (full_collections_started == _full_collections_completed + 1) ||
-         (full_collections_started == _full_collections_completed + 2),
-         err_msg("for inner caller (Full GC): full_collections_started = %u "
-                 "is inconsistent with _full_collections_completed = %u",
-                 full_collections_started, _full_collections_completed));
+         (_old_marking_cycles_started == _old_marking_cycles_completed + 1) ||
+         (_old_marking_cycles_started == _old_marking_cycles_completed + 2),
+         err_msg("for inner caller (Full GC): _old_marking_cycles_started = %u "
+                 "is inconsistent with _old_marking_cycles_completed = %u",
+                 _old_marking_cycles_started, _old_marking_cycles_completed));
 
   // This is the case for the outer caller, i.e. the concurrent cycle.
   assert(!concurrent ||
-         (full_collections_started == _full_collections_completed + 1),
+         (_old_marking_cycles_started == _old_marking_cycles_completed + 1),
          err_msg("for outer caller (concurrent cycle): "
-                 "full_collections_started = %u "
-                 "is inconsistent with _full_collections_completed = %u",
-                 full_collections_started, _full_collections_completed));
+                 "_old_marking_cycles_started = %u "
+                 "is inconsistent with _old_marking_cycles_completed = %u",
+                 _old_marking_cycles_started, _old_marking_cycles_completed));
 
-  _full_collections_completed += 1;
+  _old_marking_cycles_completed += 1;
 
   // We need to clear the "in_progress" flag in the CM thread before
   // we wake up any waiters (especially when ExplicitInvokesConcurrent
@@ -2432,7 +2438,7 @@ void G1CollectedHeap::collect(GCCause::Cause cause) {
   assert_heap_not_locked();
 
   unsigned int gc_count_before;
-  unsigned int full_gc_count_before;
+  unsigned int old_marking_count_before;
   bool retry_gc;
 
   do {
@@ -2443,7 +2449,7 @@ void G1CollectedHeap::collect(GCCause::Cause cause) {
 
       // Read the GC count while holding the Heap_lock
       gc_count_before = total_collections();
-      full_gc_count_before = total_full_collections();
+      old_marking_count_before = _old_marking_cycles_started;
     }
 
     if (should_do_concurrent_full_gc(cause)) {
@@ -2458,7 +2464,7 @@ void G1CollectedHeap::collect(GCCause::Cause cause) {
 
       VMThread::execute(&op);
       if (!op.pause_succeeded()) {
-        if (full_gc_count_before == total_full_collections()) {
+        if (old_marking_count_before == _old_marking_cycles_started) {
           retry_gc = op.should_retry_gc();
         } else {
           // A Full GC happened while we were trying to schedule the
@@ -2486,7 +2492,7 @@ void G1CollectedHeap::collect(GCCause::Cause cause) {
         VMThread::execute(&op);
       } else {
         // Schedule a Full GC.
-        VM_G1CollectFull op(gc_count_before, full_gc_count_before, cause);
+        VM_G1CollectFull op(gc_count_before, old_marking_count_before, cause);
         VMThread::execute(&op);
       }
     }
@@ -3613,7 +3619,7 @@ G1CollectedHeap::do_collection_pause_at_safepoint(double target_pause_time_ms) {
     if (g1_policy()->during_initial_mark_pause()) {
       // We are about to start a marking cycle, so we increment the
       // full collection counter.
-      increment_total_full_collections();
+      increment_old_marking_cycles_started();
     }
     // if the log level is "finer" is on, we'll print long statistics information
     // in the collector policy code, so let's not print this as the output

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

@@ -359,10 +359,13 @@ private:
   // (c) cause == _g1_humongous_allocation
   bool should_do_concurrent_full_gc(GCCause::Cause cause);
 
-  // Keeps track of how many "full collections" (i.e., Full GCs or
-  // concurrent cycles) we have completed. The number of them we have
-  // started is maintained in _total_full_collections in CollectedHeap.
-  volatile unsigned int _full_collections_completed;
+  // Keeps track of how many "old marking cycles" (i.e., Full GCs or
+  // concurrent cycles) we have started.
+  volatile unsigned int _old_marking_cycles_started;
+
+  // Keeps track of how many "old marking cycles" (i.e., Full GCs or
+  // concurrent cycles) we have completed.
+  volatile unsigned int _old_marking_cycles_completed;
 
   // This is a non-product method that is helpful for testing. It is
   // called at the end of a GC and artificially expands the heap by
@@ -673,8 +676,12 @@ public:
            (size_t) _in_cset_fast_test_length * sizeof(bool));
   }
 
+  // This is called at the start of either a concurrent cycle or a Full
+  // GC to update the number of old marking cycles started.
+  void increment_old_marking_cycles_started();
+
   // This is called at the end of either a concurrent cycle or a Full
-  // GC to update the number of full collections completed. Those two
+  // GC to update the number of old marking cycles completed. Those two
   // can happen in a nested fashion, i.e., we start a concurrent
   // cycle, a Full GC happens half-way through it which ends first,
   // and then the cycle notices that a Full GC happened and ends
@@ -683,14 +690,14 @@ public:
   // false, the caller is the inner caller in the nesting (i.e., the
   // Full GC). If concurrent is true, the caller is the outer caller
   // in this nesting (i.e., the concurrent cycle). Further nesting is
-  // not currently supported. The end of the this call also notifies
+  // not currently supported. The end of this call also notifies
   // the FullGCCount_lock in case a Java thread is waiting for a full
   // GC to happen (e.g., it called System.gc() with
   // +ExplicitGCInvokesConcurrent).
-  void increment_full_collections_completed(bool concurrent);
+  void increment_old_marking_cycles_completed(bool concurrent);
 
-  unsigned int full_collections_completed() {
-    return _full_collections_completed;
+  unsigned int old_marking_cycles_completed() {
+    return _old_marking_cycles_completed;
   }
 
   G1HRPrinter* hr_printer() { return &_hr_printer; }

src/share/vm/gc_implementation/g1/vm_operations_g1.cpp

@@ -64,7 +64,7 @@ VM_G1IncCollectionPause::VM_G1IncCollectionPause(
     _should_initiate_conc_mark(should_initiate_conc_mark),
     _target_pause_time_ms(target_pause_time_ms),
     _should_retry_gc(false),
-    _full_collections_completed_before(0) {
+    _old_marking_cycles_completed_before(0) {
   guarantee(target_pause_time_ms > 0.0,
             err_msg("target_pause_time_ms = %1.6lf should be positive",
                     target_pause_time_ms));
@@ -112,11 +112,11 @@ void VM_G1IncCollectionPause::doit() {
 
   GCCauseSetter x(g1h, _gc_cause);
   if (_should_initiate_conc_mark) {
-    // It's safer to read full_collections_completed() here, given
+    // It's safer to read old_marking_cycles_completed() here, given
     // that noone else will be updating it concurrently. Since we'll
     // only need it if we're initiating a marking cycle, no point in
     // setting it earlier.
-    _full_collections_completed_before = g1h->full_collections_completed();
+    _old_marking_cycles_completed_before = g1h->old_marking_cycles_completed();
 
     // At this point we are supposed to start a concurrent cycle. We
     // will do so if one is not already in progress.
@@ -181,17 +181,17 @@ void VM_G1IncCollectionPause::doit_epilogue() {
 
     G1CollectedHeap* g1h = G1CollectedHeap::heap();
 
-    // In the doit() method we saved g1h->full_collections_completed()
-    // in the _full_collections_completed_before field. We have to
-    // wait until we observe that g1h->full_collections_completed()
+    // In the doit() method we saved g1h->old_marking_cycles_completed()
+    // in the _old_marking_cycles_completed_before field. We have to
+    // wait until we observe that g1h->old_marking_cycles_completed()
     // has increased by at least one. This can happen if a) we started
     // a cycle and it completes, b) a cycle already in progress
     // completes, or c) a Full GC happens.
 
     // If the condition has already been reached, there's no point in
     // actually taking the lock and doing the wait.
-    if (g1h->full_collections_completed() <=
-                                          _full_collections_completed_before) {
+    if (g1h->old_marking_cycles_completed() <=
+                                          _old_marking_cycles_completed_before) {
       // The following is largely copied from CMS
 
       Thread* thr = Thread::current();
@@ -200,8 +200,8 @@ void VM_G1IncCollectionPause::doit_epilogue() {
       ThreadToNativeFromVM native(jt);
 
       MutexLockerEx x(FullGCCount_lock, Mutex::_no_safepoint_check_flag);
-      while (g1h->full_collections_completed() <=
-                                          _full_collections_completed_before) {
+      while (g1h->old_marking_cycles_completed() <=
+                                          _old_marking_cycles_completed_before) {
         FullGCCount_lock->wait(Mutex::_no_safepoint_check_flag);
       }
     }

src/share/vm/gc_implementation/g1/vm_operations_g1.hpp

@@ -80,7 +80,7 @@ private:
   bool         _should_initiate_conc_mark;
   bool         _should_retry_gc;
   double       _target_pause_time_ms;
-  unsigned int _full_collections_completed_before;
+  unsigned int _old_marking_cycles_completed_before;
 public:
   VM_G1IncCollectionPause(unsigned int   gc_count_before,
                           size_t         word_size,