--- a/hotspot/src/share/vm/gc_implementation/parNew/parNewGeneration.cpp	Sat Mar 28 15:47:29 2009 -0700
+++ b/hotspot/src/share/vm/gc_implementation/parNew/parNewGeneration.cpp	Thu Apr 02 15:57:41 2009 -0700
@@ -34,10 +34,12 @@
                                        Generation* old_gen_,
                                        int thread_num_,
                                        ObjToScanQueueSet* work_queue_set_,
+                                       GrowableArray<oop>**  overflow_stack_set_,
                                        size_t desired_plab_sz_,
                                        ParallelTaskTerminator& term_) :
   _to_space(to_space_), _old_gen(old_gen_), _young_gen(gen_), _thread_num(thread_num_),
   _work_queue(work_queue_set_->queue(thread_num_)), _to_space_full(false),
+  _overflow_stack(overflow_stack_set_[thread_num_]),
   _ageTable(false), // false ==> not the global age table, no perf data.
   _to_space_alloc_buffer(desired_plab_sz_),
   _to_space_closure(gen_, this), _old_gen_closure(gen_, this),
@@ -57,11 +59,6 @@
   _start = os::elapsedTime();
   _old_gen_closure.set_generation(old_gen_);
   _old_gen_root_closure.set_generation(old_gen_);
-  if (UseCompressedOops) {
-    _overflow_stack = new (ResourceObj::C_HEAP) GrowableArray<oop>(512, true);
-  } else {
-    _overflow_stack = NULL;
-  }
 }
 #ifdef _MSC_VER
 #pragma warning( pop )
@@ -155,7 +152,7 @@
 }
 
 bool ParScanThreadState::take_from_overflow_stack() {
-  assert(UseCompressedOops, "Else should not call");
+  assert(ParGCUseLocalOverflow, "Else should not call");
   assert(young_gen()->overflow_list() == NULL, "Error");
   ObjToScanQueue* queue = work_queue();
   GrowableArray<oop>* of_stack = overflow_stack();
@@ -183,7 +180,7 @@
 }
 
 void ParScanThreadState::push_on_overflow_stack(oop p) {
-  assert(UseCompressedOops, "Else should not call");
+  assert(ParGCUseLocalOverflow, "Else should not call");
   overflow_stack()->push(p);
   assert(young_gen()->overflow_list() == NULL, "Error");
 }
@@ -260,6 +257,7 @@
                         ParNewGeneration&       gen,
                         Generation&             old_gen,
                         ObjToScanQueueSet&      queue_set,
+                        GrowableArray<oop>**    overflow_stacks_,
                         size_t                  desired_plab_sz,
                         ParallelTaskTerminator& term);
   inline ParScanThreadState& thread_sate(int i);
@@ -282,6 +280,7 @@
 ParScanThreadStateSet::ParScanThreadStateSet(
   int num_threads, Space& to_space, ParNewGeneration& gen,
   Generation& old_gen, ObjToScanQueueSet& queue_set,
+  GrowableArray<oop>** overflow_stack_set_,
   size_t desired_plab_sz, ParallelTaskTerminator& term)
   : ResourceArray(sizeof(ParScanThreadState), num_threads),
     _gen(gen), _next_gen(old_gen), _term(term),
@@ -292,7 +291,7 @@
   for (int i = 0; i < num_threads; ++i) {
     new ((ParScanThreadState*)_data + i)
         ParScanThreadState(&to_space, &gen, &old_gen, i, &queue_set,
-                           desired_plab_sz, term);
+                           overflow_stack_set_, desired_plab_sz, term);
   }
 }
 
@@ -519,6 +518,17 @@
   for (uint i2 = 0; i2 < ParallelGCThreads; i2++)
     _task_queues->queue(i2)->initialize();
 
+  _overflow_stacks = NEW_C_HEAP_ARRAY(GrowableArray<oop>*, ParallelGCThreads);
+  guarantee(_overflow_stacks != NULL, "Overflow stack set allocation failure");
+  for (uint i = 0; i < ParallelGCThreads; i++) {
+    if (ParGCUseLocalOverflow) {
+      _overflow_stacks[i] = new (ResourceObj::C_HEAP) GrowableArray<oop>(512, true);
+      guarantee(_overflow_stacks[i] != NULL, "Overflow Stack allocation failure.");
+    } else {
+      _overflow_stacks[i] = NULL;
+    }
+  }
+
   if (UsePerfData) {
     EXCEPTION_MARK;
     ResourceMark rm;
@@ -784,7 +794,7 @@
   ParallelTaskTerminator _term(workers->total_workers(), task_queues());
   ParScanThreadStateSet thread_state_set(workers->total_workers(),
                                          *to(), *this, *_next_gen, *task_queues(),
-                                         desired_plab_sz(), _term);
+                                         _overflow_stacks, desired_plab_sz(), _term);
 
   ParNewGenTask tsk(this, _next_gen, reserved().end(), &thread_state_set);
   int n_workers = workers->total_workers();
@@ -1238,11 +1248,12 @@
 #define BUSY (oop(0x1aff1aff))
 void ParNewGeneration::push_on_overflow_list(oop from_space_obj, ParScanThreadState* par_scan_state) {
   assert(is_in_reserved(from_space_obj), "Should be from this generation");
-  if (UseCompressedOops) {
+  if (ParGCUseLocalOverflow) {
     // In the case of compressed oops, we use a private, not-shared
     // overflow stack.
     par_scan_state->push_on_overflow_stack(from_space_obj);
   } else {
+    assert(!UseCompressedOops, "Error");
     // if the object has been forwarded to itself, then we cannot
     // use the klass pointer for the linked list.  Instead we have
     // to allocate an oopDesc in the C-Heap and use that for the linked list.
@@ -1275,9 +1286,10 @@
 bool ParNewGeneration::take_from_overflow_list(ParScanThreadState* par_scan_state) {
   bool res;
 
-  if (UseCompressedOops) {
+  if (ParGCUseLocalOverflow) {
     res = par_scan_state->take_from_overflow_stack();
   } else {
+    assert(!UseCompressedOops, "Error");
     res = take_from_overflow_list_work(par_scan_state);
   }
   return res;
@@ -1305,6 +1317,7 @@
                                  (size_t)ParGCDesiredObjsFromOverflowList);
 
   assert(par_scan_state->overflow_stack() == NULL, "Error");
+  assert(!UseCompressedOops, "Error");
   if (_overflow_list == NULL) return false;
 
   // Otherwise, there was something there; try claiming the list.

--- a/hotspot/src/share/vm/gc_implementation/parNew/parNewGeneration.hpp	Sat Mar 28 15:47:29 2009 -0700
+++ b/hotspot/src/share/vm/gc_implementation/parNew/parNewGeneration.hpp	Thu Apr 02 15:57:41 2009 -0700
@@ -33,8 +33,8 @@
 // but they must be here to allow ParScanClosure::do_oop_work to be defined
 // in genOopClosures.inline.hpp.
 
-typedef OopTaskQueue    ObjToScanQueue;
-typedef OopTaskQueueSet ObjToScanQueueSet;
+typedef OopTaskQueue       ObjToScanQueue;
+typedef OopTaskQueueSet    ObjToScanQueueSet;
 
 // Enable this to get push/pop/steal stats.
 const int PAR_STATS_ENABLED = 0;
@@ -116,7 +116,9 @@
 
   ParScanThreadState(Space* to_space_, ParNewGeneration* gen_,
                      Generation* old_gen_, int thread_num_,
-                     ObjToScanQueueSet* work_queue_set_, size_t desired_plab_sz_,
+                     ObjToScanQueueSet* work_queue_set_,
+                     GrowableArray<oop>** overflow_stack_set_,
+                     size_t desired_plab_sz_,
                      ParallelTaskTerminator& term_);
 
  public:
@@ -296,9 +298,12 @@
         char pad[64 - sizeof(ObjToScanQueue)];  // prevent false sharing
   };
 
-  // The per-thread work queues, available here for stealing.
+  // The per-worker-thread work queues
   ObjToScanQueueSet* _task_queues;
 
+  // Per-worker-thread local overflow stacks
+  GrowableArray<oop>** _overflow_stacks;
+
   // Desired size of survivor space plab's
   PLABStats _plab_stats;
 

--- a/hotspot/src/share/vm/runtime/arguments.cpp	Sat Mar 28 15:47:29 2009 -0700
+++ b/hotspot/src/share/vm/runtime/arguments.cpp	Thu Apr 02 15:57:41 2009 -0700
@@ -971,7 +971,7 @@
   } else {
     no_shared_spaces();
 
-    // By default YoungPLABSize and OldPLABSize are set to 4096 and 1024 correspondinly,
+    // By default YoungPLABSize and OldPLABSize are set to 4096 and 1024 respectively,
     // these settings are default for Parallel Scavenger. For ParNew+Tenured configuration
     // we set them to 1024 and 1024.
     // See CR 6362902.
@@ -987,6 +987,16 @@
     if (AlwaysTenure) {
       FLAG_SET_CMDLINE(intx, MaxTenuringThreshold, 0);
     }
+    // When using compressed oops, we use local overflow stacks,
+    // rather than using a global overflow list chained through
+    // the klass word of the object's pre-image.
+    if (UseCompressedOops && !ParGCUseLocalOverflow) {
+      if (!FLAG_IS_DEFAULT(ParGCUseLocalOverflow)) {
+        warning("Forcing +ParGCUseLocalOverflow: needed if using compressed references");
+      }
+      FLAG_SET_DEFAULT(ParGCUseLocalOverflow, true);
+    }
+    assert(ParGCUseLocalOverflow || !UseCompressedOops, "Error");
   }
 }
 

--- a/hotspot/src/share/vm/runtime/globals.hpp	Sat Mar 28 15:47:29 2009 -0700
+++ b/hotspot/src/share/vm/runtime/globals.hpp	Thu Apr 02 15:57:41 2009 -0700
@@ -1316,8 +1316,11 @@
   product(intx, ParGCArrayScanChunk, 50,                                    \
           "Scan a subset and push remainder, if array is bigger than this") \
                                                                             \
+  product(bool, ParGCUseLocalOverflow, false,                               \
+          "Instead of a global overflow list, use local overflow stacks")   \
+                                                                            \
   product(bool, ParGCTrimOverflow, true,                                    \
-          "Eagerly trim the overflow lists (useful for UseCompressedOops")  \
+          "Eagerly trim the local overflow lists (when ParGCUseLocalOverflow") \
                                                                             \
   notproduct(bool, ParGCWorkQueueOverflowALot, false,                       \
           "Whether we should simulate work queue overflow in ParNew")       \