changeset 27152:0b4c3ec93238

Merge
author jwilhelm
date Mon, 13 Oct 2014 16:05:46 +0200
parents e326bfa8aeed 46c8a68473f0
children 078af0a29311 ccf8883e01be
files
diffstat 14 files changed, 364 insertions(+), 19 deletions(-) [+]
line wrap: on
line diff
--- a/hotspot/src/share/vm/gc_implementation/g1/concurrentMark.cpp	Fri Oct 10 02:24:35 2014 -0700
+++ b/hotspot/src/share/vm/gc_implementation/g1/concurrentMark.cpp	Mon Oct 13 16:05:46 2014 +0200
@@ -131,7 +131,10 @@
   storage->set_mapping_changed_listener(&_listener);
 }
 
-void CMBitMapMappingChangedListener::on_commit(uint start_region, size_t num_regions) {
+void CMBitMapMappingChangedListener::on_commit(uint start_region, size_t num_regions, bool zero_filled) {
+  if (zero_filled) {
+    return;
+  }
   // We need to clear the bitmap on commit, removing any existing information.
   MemRegion mr(G1CollectedHeap::heap()->bottom_addr_for_region(start_region), num_regions * HeapRegion::GrainWords);
   _bm->clearRange(mr);
--- a/hotspot/src/share/vm/gc_implementation/g1/concurrentMark.hpp	Fri Oct 10 02:24:35 2014 -0700
+++ b/hotspot/src/share/vm/gc_implementation/g1/concurrentMark.hpp	Mon Oct 13 16:05:46 2014 +0200
@@ -127,7 +127,7 @@
 
   void set_bitmap(CMBitMap* bm) { _bm = bm; }
 
-  virtual void on_commit(uint start_idx, size_t num_regions);
+  virtual void on_commit(uint start_idx, size_t num_regions, bool zero_filled);
 };
 
 class CMBitMap : public CMBitMapRO {
--- a/hotspot/src/share/vm/gc_implementation/g1/g1BlockOffsetTable.hpp	Fri Oct 10 02:24:35 2014 -0700
+++ b/hotspot/src/share/vm/gc_implementation/g1/g1BlockOffsetTable.hpp	Mon Oct 13 16:05:46 2014 +0200
@@ -109,7 +109,7 @@
 
 class G1BlockOffsetSharedArrayMappingChangedListener : public G1MappingChangedListener {
  public:
-  virtual void on_commit(uint start_idx, size_t num_regions) {
+  virtual void on_commit(uint start_idx, size_t num_regions, bool zero_filled) {
     // Nothing to do. The BOT is hard-wired to be part of the HeapRegion, and we cannot
     // retrieve it here since this would cause firing of several asserts. The code
     // executed after commit of a region already needs to do some re-initialization of
--- a/hotspot/src/share/vm/gc_implementation/g1/g1CardCounts.cpp	Fri Oct 10 02:24:35 2014 -0700
+++ b/hotspot/src/share/vm/gc_implementation/g1/g1CardCounts.cpp	Mon Oct 13 16:05:46 2014 +0200
@@ -33,7 +33,10 @@
 
 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
 
-void G1CardCountsMappingChangedListener::on_commit(uint start_idx, size_t num_regions) {
+void G1CardCountsMappingChangedListener::on_commit(uint start_idx, size_t num_regions, bool zero_filled) {
+  if (zero_filled) {
+    return;
+  }
   MemRegion mr(G1CollectedHeap::heap()->bottom_addr_for_region(start_idx), num_regions * HeapRegion::GrainWords);
   _counts->clear_range(mr);
 }
--- a/hotspot/src/share/vm/gc_implementation/g1/g1CardCounts.hpp	Fri Oct 10 02:24:35 2014 -0700
+++ b/hotspot/src/share/vm/gc_implementation/g1/g1CardCounts.hpp	Mon Oct 13 16:05:46 2014 +0200
@@ -42,7 +42,7 @@
  public:
   void set_cardcounts(G1CardCounts* counts) { _counts = counts; }
 
-  virtual void on_commit(uint start_idx, size_t num_regions);
+  virtual void on_commit(uint start_idx, size_t num_regions, bool zero_filled);
 };
 
 // Table to track the number of times a card has been refined. Once
--- a/hotspot/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp	Fri Oct 10 02:24:35 2014 -0700
+++ b/hotspot/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp	Mon Oct 13 16:05:46 2014 +0200
@@ -389,7 +389,9 @@
   OtherRegionsTable::invalidate(start_idx, num_regions);
 }
 
-void G1RegionMappingChangedListener::on_commit(uint start_idx, size_t num_regions) {
+void G1RegionMappingChangedListener::on_commit(uint start_idx, size_t num_regions, bool zero_filled) {
+  // The from card cache is not the memory that is actually committed. So we cannot
+  // take advantage of the zero_filled parameter.
   reset_from_card_cache(start_idx, num_regions);
 }
 
@@ -3610,7 +3612,7 @@
                                                                   cl.candidate_humongous());
   _has_humongous_reclaim_candidates = cl.candidate_humongous() > 0;
 
-  if (_has_humongous_reclaim_candidates) {
+  if (_has_humongous_reclaim_candidates || G1TraceReclaimDeadHumongousObjectsAtYoungGC) {
     clear_humongous_is_live_table();
   }
 }
@@ -6272,9 +6274,10 @@
         g1h->humongous_region_is_always_live(region_idx)) {
 
       if (G1TraceReclaimDeadHumongousObjectsAtYoungGC) {
-        gclog_or_tty->print_cr("Live humongous %d region %d with remset "SIZE_FORMAT" code roots "SIZE_FORMAT" is marked %d live-other %d obj array %d",
+        gclog_or_tty->print_cr("Live humongous %d region %d size "SIZE_FORMAT" with remset "SIZE_FORMAT" code roots "SIZE_FORMAT" is marked %d live-other %d obj array %d",
                                r->is_humongous(),
                                region_idx,
+                               obj->size()*HeapWordSize,
                                r->rem_set()->occupied(),
                                r->rem_set()->strong_code_roots_list_length(),
                                next_bitmap->isMarked(r->bottom()),
@@ -6291,8 +6294,9 @@
                       r->bottom()));
 
     if (G1TraceReclaimDeadHumongousObjectsAtYoungGC) {
-      gclog_or_tty->print_cr("Reclaim humongous region %d start "PTR_FORMAT" region %d length "UINT32_FORMAT" with remset "SIZE_FORMAT" code roots "SIZE_FORMAT" is marked %d live-other %d obj array %d",
+      gclog_or_tty->print_cr("Reclaim humongous region %d size "SIZE_FORMAT" start "PTR_FORMAT" region %d length "UINT32_FORMAT" with remset "SIZE_FORMAT" code roots "SIZE_FORMAT" is marked %d live-other %d obj array %d",
                              r->is_humongous(),
+                             obj->size()*HeapWordSize,
                              r->bottom(),
                              region_idx,
                              r->region_num(),
@@ -6331,7 +6335,8 @@
 void G1CollectedHeap::eagerly_reclaim_humongous_regions() {
   assert_at_safepoint(true);
 
-  if (!G1ReclaimDeadHumongousObjectsAtYoungGC || !_has_humongous_reclaim_candidates) {
+  if (!G1ReclaimDeadHumongousObjectsAtYoungGC ||
+      (!_has_humongous_reclaim_candidates && !G1TraceReclaimDeadHumongousObjectsAtYoungGC)) {
     g1_policy()->phase_times()->record_fast_reclaim_humongous_time_ms(0.0, 0);
     return;
   }
--- a/hotspot/src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp	Fri Oct 10 02:24:35 2014 -0700
+++ b/hotspot/src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp	Mon Oct 13 16:05:46 2014 +0200
@@ -172,7 +172,7 @@
  private:
   void reset_from_card_cache(uint start_idx, size_t num_regions);
  public:
-  virtual void on_commit(uint start_idx, size_t num_regions);
+  virtual void on_commit(uint start_idx, size_t num_regions, bool zero_filled);
 };
 
 class G1CollectedHeap : public SharedHeap {
--- a/hotspot/src/share/vm/gc_implementation/g1/g1RegionToSpaceMapper.cpp	Fri Oct 10 02:24:35 2014 -0700
+++ b/hotspot/src/share/vm/gc_implementation/g1/g1RegionToSpaceMapper.cpp	Mon Oct 13 16:05:46 2014 +0200
@@ -69,7 +69,7 @@
   virtual void commit_regions(uintptr_t start_idx, size_t num_regions) {
     _storage.commit(start_idx * _pages_per_region, num_regions * _pages_per_region);
     _commit_map.set_range(start_idx, start_idx + num_regions);
-    fire_on_commit(start_idx, num_regions);
+    fire_on_commit(start_idx, num_regions, true);
   }
 
   virtual void uncommit_regions(uintptr_t start_idx, size_t num_regions) {
@@ -115,12 +115,14 @@
       assert(!_commit_map.at(i), err_msg("Trying to commit storage at region "INTPTR_FORMAT" that is already committed", i));
       uintptr_t idx = region_idx_to_page_idx(i);
       uint old_refcount = _refcounts.get_by_index(idx);
+      bool zero_filled = false;
       if (old_refcount == 0) {
         _storage.commit(idx, 1);
+        zero_filled = true;
       }
       _refcounts.set_by_index(idx, old_refcount + 1);
       _commit_map.set_bit(i);
-      fire_on_commit(i, 1);
+      fire_on_commit(i, 1, zero_filled);
     }
   }
 
@@ -139,9 +141,9 @@
   }
 };
 
-void G1RegionToSpaceMapper::fire_on_commit(uint start_idx, size_t num_regions) {
+void G1RegionToSpaceMapper::fire_on_commit(uint start_idx, size_t num_regions, bool zero_filled) {
   if (_listener != NULL) {
-    _listener->on_commit(start_idx, num_regions);
+    _listener->on_commit(start_idx, num_regions, zero_filled);
   }
 }
 
--- a/hotspot/src/share/vm/gc_implementation/g1/g1RegionToSpaceMapper.hpp	Fri Oct 10 02:24:35 2014 -0700
+++ b/hotspot/src/share/vm/gc_implementation/g1/g1RegionToSpaceMapper.hpp	Mon Oct 13 16:05:46 2014 +0200
@@ -33,7 +33,9 @@
  public:
   // Fired after commit of the memory, i.e. the memory this listener is registered
   // for can be accessed.
-  virtual void on_commit(uint start_idx, size_t num_regions) = 0;
+  // Zero_filled indicates that the memory can be considered as filled with zero bytes
+  // when called.
+  virtual void on_commit(uint start_idx, size_t num_regions, bool zero_filled) = 0;
 };
 
 // Maps region based commit/uncommit requests to the underlying page sized virtual
@@ -51,7 +53,7 @@
 
   G1RegionToSpaceMapper(ReservedSpace rs, size_t commit_granularity, size_t region_granularity, MemoryType type);
 
-  void fire_on_commit(uint start_idx, size_t num_regions);
+  void fire_on_commit(uint start_idx, size_t num_regions, bool zero_filled);
  public:
   MemRegion reserved() { return _storage.reserved(); }
 
--- a/hotspot/src/share/vm/gc_implementation/g1/g1SATBCardTableModRefBS.cpp	Fri Oct 10 02:24:35 2014 -0700
+++ b/hotspot/src/share/vm/gc_implementation/g1/g1SATBCardTableModRefBS.cpp	Mon Oct 13 16:05:46 2014 +0200
@@ -125,7 +125,8 @@
 }
 #endif
 
-void G1SATBCardTableLoggingModRefBSChangedListener::on_commit(uint start_idx, size_t num_regions) {
+void G1SATBCardTableLoggingModRefBSChangedListener::on_commit(uint start_idx, size_t num_regions, bool zero_filled) {
+  // Default value for a clean card on the card table is -1. So we cannot take advantage of the zero_filled parameter.
   MemRegion mr(G1CollectedHeap::heap()->bottom_addr_for_region(start_idx), num_regions * HeapRegion::GrainWords);
   _card_table->clear(mr);
 }
--- a/hotspot/src/share/vm/gc_implementation/g1/g1SATBCardTableModRefBS.hpp	Fri Oct 10 02:24:35 2014 -0700
+++ b/hotspot/src/share/vm/gc_implementation/g1/g1SATBCardTableModRefBS.hpp	Mon Oct 13 16:05:46 2014 +0200
@@ -136,7 +136,7 @@
 
   void set_card_table(G1SATBCardTableLoggingModRefBS* card_table) { _card_table = card_table; }
 
-  virtual void on_commit(uint start_idx, size_t num_regions);
+  virtual void on_commit(uint start_idx, size_t num_regions, bool zero_filled);
 };
 
 // Adds card-table logging to the post-barrier.
--- a/hotspot/src/share/vm/opto/graphKit.cpp	Fri Oct 10 02:24:35 2014 -0700
+++ b/hotspot/src/share/vm/opto/graphKit.cpp	Mon Oct 13 16:05:46 2014 +0200
@@ -3826,6 +3826,110 @@
   // Final sync IdealKit and GraphKit.
   final_sync(ideal);
 }
+/*
+ * Determine if the G1 pre-barrier can be removed. The pre-barrier is
+ * required by SATB to make sure all objects live at the start of the
+ * marking are kept alive, all reference updates need to any previous
+ * reference stored before writing.
+ *
+ * If the previous value is NULL there is no need to save the old value.
+ * References that are NULL are filtered during runtime by the barrier
+ * code to avoid unnecessary queuing.
+ *
+ * However in the case of newly allocated objects it might be possible to
+ * prove that the reference about to be overwritten is NULL during compile
+ * time and avoid adding the barrier code completely.
+ *
+ * The compiler needs to determine that the object in which a field is about
+ * to be written is newly allocated, and that no prior store to the same field
+ * has happened since the allocation.
+ *
+ * Returns true if the pre-barrier can be removed
+ */
+bool GraphKit::g1_can_remove_pre_barrier(PhaseTransform* phase, Node* adr,
+                                         BasicType bt, uint adr_idx) {
+  intptr_t offset = 0;
+  Node* base = AddPNode::Ideal_base_and_offset(adr, phase, offset);
+  AllocateNode* alloc = AllocateNode::Ideal_allocation(base, phase);
+
+  if (offset == Type::OffsetBot) {
+    return false; // cannot unalias unless there are precise offsets
+  }
+
+  if (alloc == NULL) {
+    return false; // No allocation found
+  }
+
+  intptr_t size_in_bytes = type2aelembytes(bt);
+
+  Node* mem = memory(adr_idx); // start searching here...
+
+  for (int cnt = 0; cnt < 50; cnt++) {
+
+    if (mem->is_Store()) {
+
+      Node* st_adr = mem->in(MemNode::Address);
+      intptr_t st_offset = 0;
+      Node* st_base = AddPNode::Ideal_base_and_offset(st_adr, phase, st_offset);
+
+      if (st_base == NULL) {
+        break; // inscrutable pointer
+      }
+
+      // Break we have found a store with same base and offset as ours so break
+      if (st_base == base && st_offset == offset) {
+        break;
+      }
+
+      if (st_offset != offset && st_offset != Type::OffsetBot) {
+        const int MAX_STORE = BytesPerLong;
+        if (st_offset >= offset + size_in_bytes ||
+            st_offset <= offset - MAX_STORE ||
+            st_offset <= offset - mem->as_Store()->memory_size()) {
+          // Success:  The offsets are provably independent.
+          // (You may ask, why not just test st_offset != offset and be done?
+          // The answer is that stores of different sizes can co-exist
+          // in the same sequence of RawMem effects.  We sometimes initialize
+          // a whole 'tile' of array elements with a single jint or jlong.)
+          mem = mem->in(MemNode::Memory);
+          continue; // advance through independent store memory
+        }
+      }
+
+      if (st_base != base
+          && MemNode::detect_ptr_independence(base, alloc, st_base,
+                                              AllocateNode::Ideal_allocation(st_base, phase),
+                                              phase)) {
+        // Success:  The bases are provably independent.
+        mem = mem->in(MemNode::Memory);
+        continue; // advance through independent store memory
+      }
+    } else if (mem->is_Proj() && mem->in(0)->is_Initialize()) {
+
+      InitializeNode* st_init = mem->in(0)->as_Initialize();
+      AllocateNode* st_alloc = st_init->allocation();
+
+      // Make sure that we are looking at the same allocation site.
+      // The alloc variable is guaranteed to not be null here from earlier check.
+      if (alloc == st_alloc) {
+        // Check that the initialization is storing NULL so that no previous store
+        // has been moved up and directly write a reference
+        Node* captured_store = st_init->find_captured_store(offset,
+                                                            type2aelembytes(T_OBJECT),
+                                                            phase);
+        if (captured_store == NULL || captured_store == st_init->zero_memory()) {
+          return true;
+        }
+      }
+    }
+
+    // Unless there is an explicit 'continue', we must bail out here,
+    // because 'mem' is an inscrutable memory state (e.g., a call).
+    break;
+  }
+
+  return false;
+}
 
 // G1 pre/post barriers
 void GraphKit::g1_write_barrier_pre(bool do_load,
@@ -3846,6 +3950,12 @@
     assert(adr != NULL, "where are loading from?");
     assert(pre_val == NULL, "loaded already?");
     assert(val_type != NULL, "need a type");
+
+    if (use_ReduceInitialCardMarks()
+        && g1_can_remove_pre_barrier(&_gvn, adr, bt, alias_idx)) {
+      return;
+    }
+
   } else {
     // In this case both val_type and alias_idx are unused.
     assert(pre_val != NULL, "must be loaded already");
@@ -3927,6 +4037,65 @@
   final_sync(ideal);
 }
 
+/*
+ * G1 similar to any GC with a Young Generation requires a way to keep track of
+ * references from Old Generation to Young Generation to make sure all live
+ * objects are found. G1 also requires to keep track of object references
+ * between different regions to enable evacuation of old regions, which is done
+ * as part of mixed collections. References are tracked in remembered sets and
+ * is continuously updated as reference are written to with the help of the
+ * post-barrier.
+ *
+ * To reduce the number of updates to the remembered set the post-barrier
+ * filters updates to fields in objects located in the Young Generation,
+ * the same region as the reference, when the NULL is being written or
+ * if the card is already marked as dirty by an earlier write.
+ *
+ * Under certain circumstances it is possible to avoid generating the
+ * post-barrier completely if it is possible during compile time to prove
+ * the object is newly allocated and that no safepoint exists between the
+ * allocation and the store.
+ *
+ * In the case of slow allocation the allocation code must handle the barrier
+ * as part of the allocation in the case the allocated object is not located
+ * in the nursery, this would happen for humongous objects. This is similar to
+ * how CMS is required to handle this case, see the comments for the method
+ * CollectedHeap::new_store_pre_barrier and OptoRuntime::new_store_pre_barrier.
+ * A deferred card mark is required for these objects and handled in the above
+ * mentioned methods.
+ *
+ * Returns true if the post barrier can be removed
+ */
+bool GraphKit::g1_can_remove_post_barrier(PhaseTransform* phase, Node* store,
+                                          Node* adr) {
+  intptr_t      offset = 0;
+  Node*         base   = AddPNode::Ideal_base_and_offset(adr, phase, offset);
+  AllocateNode* alloc  = AllocateNode::Ideal_allocation(base, phase);
+
+  if (offset == Type::OffsetBot) {
+    return false; // cannot unalias unless there are precise offsets
+  }
+
+  if (alloc == NULL) {
+     return false; // No allocation found
+  }
+
+  // Start search from Store node
+  Node* mem = store->in(MemNode::Control);
+  if (mem->is_Proj() && mem->in(0)->is_Initialize()) {
+
+    InitializeNode* st_init = mem->in(0)->as_Initialize();
+    AllocateNode*  st_alloc = st_init->allocation();
+
+    // Make sure we are looking at the same allocation
+    if (alloc == st_alloc) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
 //
 // Update the card table and add card address to the queue
 //
@@ -3979,6 +4148,20 @@
     return;
   }
 
+  if (use_ReduceInitialCardMarks() && obj == just_allocated_object(control())) {
+    // We can skip marks on a freshly-allocated object in Eden.
+    // Keep this code in sync with new_store_pre_barrier() in runtime.cpp.
+    // That routine informs GC to take appropriate compensating steps,
+    // upon a slow-path allocation, so as to make this card-mark
+    // elision safe.
+    return;
+  }
+
+  if (use_ReduceInitialCardMarks()
+      && g1_can_remove_post_barrier(&_gvn, oop_store, adr)) {
+    return;
+  }
+
   if (!use_precise) {
     // All card marks for a (non-array) instance are in one place:
     adr = obj;
--- a/hotspot/src/share/vm/opto/graphKit.hpp	Fri Oct 10 02:24:35 2014 -0700
+++ b/hotspot/src/share/vm/opto/graphKit.hpp	Mon Oct 13 16:05:46 2014 +0200
@@ -771,6 +771,10 @@
                     Node* index, Node* index_adr,
                     Node* buffer, const TypeFunc* tf);
 
+  bool g1_can_remove_pre_barrier(PhaseTransform* phase, Node* adr, BasicType bt, uint adr_idx);
+
+  bool g1_can_remove_post_barrier(PhaseTransform* phase, Node* store, Node* adr);
+
   public:
   // Helper function to round double arguments before a call
   void round_double_arguments(ciMethod* dest_method);
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/hotspot/test/gc/g1/TestG1TraceReclaimDeadHumongousObjectsAtYoungGC.java	Mon Oct 13 16:05:46 2014 +0200
@@ -0,0 +1,142 @@
+/*
+ * Copyright (c) 2014, Oracle and/or its affiliates. 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.
+ *
+ * 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.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test TestG1TraceReclaimDeadHumongousObjectsAtYoungGC
+ * @bug 8058801
+ * @summary Ensure that the output for a G1TraceReclaimDeadHumongousObjectsAtYoungGC
+ * includes the expected necessary messages.
+ * @key gc
+ * @library /testlibrary
+ */
+
+import com.oracle.java.testlibrary.ProcessTools;
+import com.oracle.java.testlibrary.OutputAnalyzer;
+import java.util.LinkedList;
+
+public class TestG1TraceReclaimDeadHumongousObjectsAtYoungGC {
+  public static void main(String[] args) throws Exception {
+    testGCLogs();
+    testHumongousObjectGCLogs();
+  }
+
+  private static void testGCLogs() throws Exception {
+
+    ProcessBuilder pb = ProcessTools.createJavaProcessBuilder("-XX:+UseG1GC",
+                                               "-Xms128M",
+                                               "-Xmx128M",
+                                               "-Xmn16M",
+                                               "-XX:G1HeapRegionSize=1M",
+                                               "-XX:+PrintGC",
+                                               "-XX:+UnlockExperimentalVMOptions",
+                                               "-XX:G1LogLevel=finest",
+                                               "-XX:+G1TraceReclaimDeadHumongousObjectsAtYoungGC",
+                                               GCTest.class.getName());
+
+    OutputAnalyzer output = new OutputAnalyzer(pb.start());
+
+    // As G1ReclaimDeadHumongousObjectsAtYoungGC is set(default), below logs should be displayed.
+    // And GCTest doesn't have humongous objects, so values should be zero.
+    output.shouldContain("[Humongous Reclaim");
+    output.shouldContain("[Humongous Total: 0]");
+    output.shouldContain("[Humongous Candidate: 0]");
+    output.shouldContain("[Humongous Reclaimed: 0]");
+
+    output.shouldHaveExitValue(0);
+  }
+
+  private static void testHumongousObjectGCLogs() throws Exception {
+    ProcessBuilder pb = ProcessTools.createJavaProcessBuilder("-XX:+UseG1GC",
+                                               "-Xms128M",
+                                               "-Xmx128M",
+                                               "-Xmn16M",
+                                               "-XX:G1HeapRegionSize=1M",
+                                               "-XX:+PrintGC",
+                                               "-XX:+UnlockExperimentalVMOptions",
+                                               "-XX:G1LogLevel=finest",
+                                               "-XX:+G1TraceReclaimDeadHumongousObjectsAtYoungGC",
+                                               GCWithHumongousObjectTest.class.getName());
+
+    OutputAnalyzer output = new OutputAnalyzer(pb.start());
+
+    // As G1ReclaimDeadHumongousObjectsAtYoungGC is set(default), below logs should be displayed.
+    output.shouldContain("[Humongous Reclaim");
+    output.shouldContain("[Humongous Total");
+    output.shouldContain("[Humongous Candidate");
+    output.shouldContain("[Humongous Reclaimed");
+
+    // As G1TraceReclaimDeadHumongousObjectsAtYoungGC is set and GCWithHumongousObjectTest has humongous objects,
+    // these logs should be displayed.
+    output.shouldContain("Live humongous");
+    output.shouldContain("Reclaim humongous region");
+    output.shouldHaveExitValue(0);
+  }
+
+  static class GCTest {
+    private static byte[] garbage;
+
+    public static void main(String [] args) {
+      System.out.println("Creating garbage");
+      // create 128MB of garbage. This should result in at least one GC
+      for (int i = 0; i < 1024; i++) {
+        garbage = new byte[128 * 1024];
+      }
+      System.out.println("Done");
+    }
+  }
+
+  static class GCWithHumongousObjectTest {
+
+    public static final int M = 1024*1024;
+    public static LinkedList<Object> garbageList = new LinkedList<Object>();
+    // A large object referenced by a static.
+    static int[] filler = new int[10 * M];
+
+    public static void genGarbage() {
+      for (int i = 0; i < 32*1024; i++) {
+        garbageList.add(new int[100]);
+      }
+      garbageList.clear();
+    }
+
+    public static void main(String[] args) {
+
+      int[] large = new int[M];
+      Object ref = large;
+
+      System.out.println("Creating garbage");
+      for (int i = 0; i < 100; i++) {
+        // A large object that will be reclaimed eagerly.
+        large = new int[6*M];
+        genGarbage();
+        // Make sure that the compiler cannot completely remove
+        // the allocation of the large object until here.
+        System.out.println(large);
+      }
+
+      // Keep the reference to the first object alive.
+      System.out.println(ref);
+      System.out.println("Done");
+    }
+  }
+}