From dfbf634505d98e7e8e20b9b1dff578c4115892e0 Mon Sep 17 00:00:00 2001
From: tonyp <unknown>
Date: Tue, 19 Apr 2011 15:46:59 -0400
Subject: [PATCH] 7011855: G1: non-product flag to artificially grow the heap
 Summary: It introduces non-product cmd line parameter G1DummyRegionsPerGC
 which indicates how many "dummy" regions to allocate at the end of each GC.
 This allows the G1 heap to grow artificially and makes concurrent marking
 cycles more frequent irrespective of what the application that is running is
 doing. The dummy regions will be found totally empty during cleanup so this
 parameter can also be used to stress the concurrent cleanup operation.
 Reviewed-by: brutisso, johnc

---
 .../gc_implementation/g1/g1CollectedHeap.cpp  | 24 +++++++++++++++++++
 .../gc_implementation/g1/g1CollectedHeap.hpp  |  8 +++++++
 .../vm/gc_implementation/g1/g1_globals.hpp    |  5 ++++
 3 files changed, 37 insertions(+)

diff --git a/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp b/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp
index 1c2b116a5..becc94512 100644
--- a/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp
+++ b/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp
@@ -2113,6 +2113,28 @@ bool G1CollectedHeap::should_do_concurrent_full_gc(GCCause::Cause cause) {
      (cause == GCCause::_java_lang_system_gc && ExplicitGCInvokesConcurrent));
 }
 
+#ifndef PRODUCT
+void G1CollectedHeap::allocate_dummy_regions() {
+  // Let's fill up most of the region
+  size_t word_size = HeapRegion::GrainWords - 1024;
+  // And as a result the region we'll allocate will be humongous.
+  guarantee(isHumongous(word_size), "sanity");
+
+  for (uintx i = 0; i < G1DummyRegionsPerGC; ++i) {
+    // Let's use the existing mechanism for the allocation
+    HeapWord* dummy_obj = humongous_obj_allocate(word_size);
+    if (dummy_obj != NULL) {
+      MemRegion mr(dummy_obj, word_size);
+      CollectedHeap::fill_with_object(mr);
+    } else {
+      // If we can't allocate once, we probably cannot allocate
+      // again. Let's get out of the loop.
+      break;
+    }
+  }
+}
+#endif // !PRODUCT
+
 void G1CollectedHeap::increment_full_collections_completed(bool concurrent) {
   MonitorLockerEx x(FullGCCount_lock, Mutex::_no_safepoint_check_flag);
 
@@ -3338,6 +3360,8 @@ G1CollectedHeap::do_collection_pause_at_safepoint(double target_pause_time_ms) {
         doConcurrentMark();
       }
 
+      allocate_dummy_regions();
+
 #if YOUNG_LIST_VERBOSE
       gclog_or_tty->print_cr("\nEnd of the pause.\nYoung_list:");
       _young_list->print();
diff --git a/src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp b/src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp
index a94127744..1b7e6a307 100644
--- a/src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp
+++ b/src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp
@@ -298,6 +298,14 @@ private:
   // started is maintained in _total_full_collections in CollectedHeap.
   volatile unsigned int _full_collections_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
+  // allocating a number of dead regions. This way we can induce very
+  // frequent marking cycles and stress the cleanup / concurrent
+  // cleanup code more (as all the regions that will be allocated by
+  // this method will be found dead by the marking cycle).
+  void allocate_dummy_regions() PRODUCT_RETURN;
+
   // These are macros so that, if the assert fires, we get the correct
   // line number, file, etc.
 
diff --git a/src/share/vm/gc_implementation/g1/g1_globals.hpp b/src/share/vm/gc_implementation/g1/g1_globals.hpp
index 5fd535533..cea902401 100644
--- a/src/share/vm/gc_implementation/g1/g1_globals.hpp
+++ b/src/share/vm/gc_implementation/g1/g1_globals.hpp
@@ -300,6 +300,11 @@
   develop(uintx, G1StressConcRegionFreeingDelayMillis, 0,                   \
           "Artificial delay during concurrent region freeing")              \
                                                                             \
+  develop(uintx, G1DummyRegionsPerGC, 0,                                    \
+          "The number of dummy regions G1 will allocate at the end of "     \
+          "each evacuation pause in order to artificially fill up the "     \
+          "heap and stress the marking implementation.")                    \
+                                                                            \
   develop(bool, ReduceInitialCardMarksForG1, false,                         \
           "When ReduceInitialCardMarks is true, this flag setting "         \
           " controls whether G1 allows the RICM optimization")              \
-- 
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