--- a/hotspot/src/share/vm/gc_implementation/g1/g1Allocator.cpp	Fri Feb 27 19:52:48 2015 -0500
+++ b/hotspot/src/share/vm/gc_implementation/g1/g1Allocator.cpp	Tue Mar 03 12:38:42 2015 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2014, 2015, 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
@@ -120,7 +120,7 @@
   if (word_sz * 100 < gclab_word_size * ParallelGCBufferWastePct) {
     G1ParGCAllocBuffer* alloc_buf = alloc_buffer(dest, context);
     add_to_alloc_buffer_waste(alloc_buf->words_remaining());
-    alloc_buf->retire(false /* end_of_gc */, false /* retain */);
+    alloc_buf->retire();
 
     HeapWord* buf = _g1h->par_allocate_during_gc(dest, gclab_word_size, context);
     if (buf == NULL) {
@@ -154,9 +154,7 @@
     G1ParGCAllocBuffer* const buf = _alloc_buffers[state];
     if (buf != NULL) {
       add_to_alloc_buffer_waste(buf->words_remaining());
-      buf->flush_stats_and_retire(_g1h->alloc_buffer_stats(state),
-                                  true /* end_of_gc */,
-                                  false /* retain */);
+      buf->flush_and_retire_stats(_g1h->alloc_buffer_stats(state));
     }
   }
 }

--- a/hotspot/src/share/vm/gc_implementation/g1/g1Allocator.hpp	Fri Feb 27 19:52:48 2015 -0500
+++ b/hotspot/src/share/vm/gc_implementation/g1/g1Allocator.hpp	Tue Mar 03 12:38:42 2015 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2014, 2015, 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
@@ -159,11 +159,11 @@
     _retired = false;
   }
 
-  virtual void retire(bool end_of_gc, bool retain) {
+  virtual void retire() {
     if (_retired) {
       return;
     }
-    ParGCAllocBuffer::retire(end_of_gc, retain);
+    ParGCAllocBuffer::retire();
     _retired = true;
   }
 };

--- a/hotspot/src/share/vm/gc_implementation/parNew/parNewGeneration.cpp	Fri Feb 27 19:52:48 2015 -0500
+++ b/hotspot/src/share/vm/gc_implementation/parNew/parNewGeneration.cpp	Tue Mar 03 12:38:42 2015 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2014, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2015, 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
@@ -232,7 +232,7 @@
     if (word_sz * 100 <
         ParallelGCBufferWastePct * plab->word_sz()) {
       // Is small enough; abandon this buffer and start a new one.
-      plab->retire(false, false);
+      plab->retire();
       size_t buf_size = plab->word_sz();
       HeapWord* buf_space = sp->par_allocate(buf_size);
       if (buf_space == NULL) {
@@ -463,10 +463,7 @@
 
     // Flush stats related to To-space PLAB activity and
     // retire the last buffer.
-    par_scan_state.to_space_alloc_buffer()->
-      flush_stats_and_retire(_gen.plab_stats(),
-                             true /* end_of_gc */,
-                             false /* retain */);
+    par_scan_state.to_space_alloc_buffer()->flush_and_retire_stats(_gen.plab_stats());
 
     // Every thread has its own age table.  We need to merge
     // them all into one.

--- a/hotspot/src/share/vm/gc_implementation/shared/parGCAllocBuffer.cpp	Fri Feb 27 19:52:48 2015 -0500
+++ b/hotspot/src/share/vm/gc_implementation/shared/parGCAllocBuffer.cpp	Tue Mar 03 12:38:42 2015 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2014, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2015, 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
@@ -24,27 +24,30 @@
 
 #include "precompiled.hpp"
 #include "gc_implementation/shared/parGCAllocBuffer.hpp"
-#include "memory/sharedHeap.hpp"
+#include "memory/threadLocalAllocBuffer.hpp"
 #include "oops/arrayOop.hpp"
 #include "oops/oop.inline.hpp"
-#include "utilities/globalDefinitions.hpp"
 
-PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
+size_t ParGCAllocBuffer::min_size() {
+  // Make sure that we return something that is larger than AlignmentReserve
+  return align_object_size(MAX2(MinTLABSize / HeapWordSize, (uintx)oopDesc::header_size())) + AlignmentReserve;
+}
+
+size_t ParGCAllocBuffer::max_size() {
+  return ThreadLocalAllocBuffer::max_size();
+}
 
 ParGCAllocBuffer::ParGCAllocBuffer(size_t desired_plab_sz_) :
   _word_sz(desired_plab_sz_), _bottom(NULL), _top(NULL),
-  _end(NULL), _hard_end(NULL),
-  _retained(false), _retained_filler(),
-  _allocated(0), _wasted(0)
+  _end(NULL), _hard_end(NULL), _allocated(0), _wasted(0)
 {
-  assert (min_size() > AlignmentReserve, "Inconsistency!");
-  // arrayOopDesc::header_size depends on command line initialization.
-  FillerHeaderSize = align_object_size(arrayOopDesc::header_size(T_INT));
-  AlignmentReserve = oopDesc::header_size() > MinObjAlignment ? FillerHeaderSize : 0;
+  // ArrayOopDesc::header_size depends on command line initialization.
+  AlignmentReserve = oopDesc::header_size() > MinObjAlignment ? align_object_size(arrayOopDesc::header_size(T_INT)) : 0;
+  assert(min_size() > AlignmentReserve,
+         err_msg("Minimum PLAB size " SIZE_FORMAT" must be larger than alignment reserve " SIZE_FORMAT" "
+                 "to be able to contain objects", min_size(), AlignmentReserve));
 }
 
-size_t ParGCAllocBuffer::FillerHeaderSize;
-
 // If the minimum object size is greater than MinObjAlignment, we can
 // end up with a shard at the end of the buffer that's smaller than
 // the smallest object.  We can't allow that because the buffer must
@@ -52,39 +55,33 @@
 // sure we have enough space for a filler int array object.
 size_t ParGCAllocBuffer::AlignmentReserve;
 
-void ParGCAllocBuffer::retire(bool end_of_gc, bool retain) {
-  assert(!retain || end_of_gc, "Can only retain at GC end.");
-  if (_retained) {
-    // If the buffer had been retained shorten the previous filler object.
-    assert(_retained_filler.end() <= _top, "INVARIANT");
-    CollectedHeap::fill_with_object(_retained_filler);
-    // Wasted space book-keeping, otherwise (normally) done in invalidate()
-    _wasted += _retained_filler.word_size();
-    _retained = false;
-  }
-  assert(!end_of_gc || !_retained, "At this point, end_of_gc ==> !_retained.");
+void ParGCAllocBuffer::flush_and_retire_stats(PLABStats* stats) {
+  // Retire the last allocation buffer.
+  size_t unused = retire_internal();
+
+  // Now flush the statistics.
+  stats->add_allocated(_allocated);
+  stats->add_wasted(_wasted);
+  stats->add_unused(unused);
+
+  // Since we have flushed the stats we need to clear  the _allocated and _wasted
+  // fields in case somebody retains an instance of this over GCs. Not doing so
+  // will artifically inflate the values in the statistics.
+  _allocated = 0;
+  _wasted = 0;
+}
+
+void ParGCAllocBuffer::retire() {
+  _wasted += retire_internal();
+}
+
+size_t ParGCAllocBuffer::retire_internal() {
+  size_t result = 0;
   if (_top < _hard_end) {
     CollectedHeap::fill_with_object(_top, _hard_end);
-    if (!retain) {
-      invalidate();
-    } else {
-      // Is there wasted space we'd like to retain for the next GC?
-      if (pointer_delta(_end, _top) > FillerHeaderSize) {
-        _retained = true;
-        _retained_filler = MemRegion(_top, FillerHeaderSize);
-        _top = _top + FillerHeaderSize;
-      } else {
-        invalidate();
-      }
-    }
+    result += invalidate();
   }
-}
-
-void ParGCAllocBuffer::flush_stats(PLABStats* stats) {
-  assert(ResizePLAB, "Wasted work");
-  stats->add_allocated(_allocated);
-  stats->add_wasted(_wasted);
-  stats->add_unused(pointer_delta(_end, _top));
+  return result;
 }
 
 // Compute desired plab size and latch result for later
@@ -101,44 +98,37 @@
            err_msg("Inconsistency in PLAB stats: "
                    "_allocated: "SIZE_FORMAT", "
                    "_wasted: "SIZE_FORMAT", "
-                   "_unused: "SIZE_FORMAT", "
-                   "_used  : "SIZE_FORMAT,
-                   _allocated, _wasted, _unused, _used));
+                   "_unused: "SIZE_FORMAT,
+                   _allocated, _wasted, _unused));
 
     _allocated = 1;
   }
-  double wasted_frac    = (double)_unused/(double)_allocated;
-  size_t target_refills = (size_t)((wasted_frac*TargetSurvivorRatio)/
-                                   TargetPLABWastePct);
+  double wasted_frac    = (double)_unused / (double)_allocated;
+  size_t target_refills = (size_t)((wasted_frac * TargetSurvivorRatio) / TargetPLABWastePct);
   if (target_refills == 0) {
     target_refills = 1;
   }
-  _used = _allocated - _wasted - _unused;
-  size_t plab_sz = _used/(target_refills*no_of_gc_workers);
-  if (PrintPLAB) gclog_or_tty->print(" (plab_sz = " SIZE_FORMAT " ", plab_sz);
+  size_t used = _allocated - _wasted - _unused;
+  size_t recent_plab_sz = used / (target_refills * no_of_gc_workers);
   // Take historical weighted average
-  _filter.sample(plab_sz);
+  _filter.sample(recent_plab_sz);
   // Clip from above and below, and align to object boundary
-  plab_sz = MAX2(min_size(), (size_t)_filter.average());
-  plab_sz = MIN2(max_size(), plab_sz);
-  plab_sz = align_object_size(plab_sz);
+  size_t new_plab_sz = MAX2(min_size(), (size_t)_filter.average());
+  new_plab_sz = MIN2(max_size(), new_plab_sz);
+  new_plab_sz = align_object_size(new_plab_sz);
   // Latch the result
-  if (PrintPLAB) gclog_or_tty->print(" desired_plab_sz = " SIZE_FORMAT ") ", plab_sz);
-  _desired_plab_sz = plab_sz;
-  // Now clear the accumulators for next round:
-  // note this needs to be fixed in the case where we
-  // are retaining across scavenges. FIX ME !!! XXX
-  _allocated = 0;
-  _wasted    = 0;
-  _unused    = 0;
+  if (PrintPLAB) {
+    gclog_or_tty->print(" (plab_sz = " SIZE_FORMAT" desired_plab_sz = " SIZE_FORMAT") ", recent_plab_sz, new_plab_sz);
+  }
+  _desired_plab_sz = new_plab_sz;
+
+  reset();
 }
 
 #ifndef PRODUCT
 void ParGCAllocBuffer::print() {
-  gclog_or_tty->print("parGCAllocBuffer: _bottom: " PTR_FORMAT "  _top: " PTR_FORMAT
-             "  _end: " PTR_FORMAT "  _hard_end: " PTR_FORMAT " _retained: %c"
-             " _retained_filler: [" PTR_FORMAT "," PTR_FORMAT ")\n",
-             _bottom, _top, _end, _hard_end,
-             "FT"[_retained], _retained_filler.start(), _retained_filler.end());
+  gclog_or_tty->print_cr("parGCAllocBuffer: _bottom: " PTR_FORMAT "  _top: " PTR_FORMAT
+    "  _end: " PTR_FORMAT "  _hard_end: " PTR_FORMAT ")",
+    p2i(_bottom), p2i(_top), p2i(_end), p2i(_hard_end));
 }
 #endif // !PRODUCT

--- a/hotspot/src/share/vm/gc_implementation/shared/parGCAllocBuffer.hpp	Fri Feb 27 19:52:48 2015 -0500
+++ b/hotspot/src/share/vm/gc_implementation/shared/parGCAllocBuffer.hpp	Tue Mar 03 12:38:42 2015 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2013, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2015, 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
@@ -24,37 +24,43 @@
 
 #ifndef SHARE_VM_GC_IMPLEMENTATION_PARNEW_PARGCALLOCBUFFER_HPP
 #define SHARE_VM_GC_IMPLEMENTATION_PARNEW_PARGCALLOCBUFFER_HPP
-#include "gc_interface/collectedHeap.hpp"
+
+#include "gc_implementation/shared/gcUtil.hpp"
 #include "memory/allocation.hpp"
-#include "memory/blockOffsetTable.hpp"
-#include "memory/threadLocalAllocBuffer.hpp"
+#include "runtime/atomic.hpp"
 #include "utilities/globalDefinitions.hpp"
 
-// Forward decl.
-
+// Forward declarations.
 class PLABStats;
 
 // A per-thread allocation buffer used during GC.
 class ParGCAllocBuffer: public CHeapObj<mtGC> {
 protected:
-  char head[32];
-  size_t _word_sz;          // in HeapWord units
+  char      head[32];
+  size_t    _word_sz;          // In HeapWord units
   HeapWord* _bottom;
   HeapWord* _top;
-  HeapWord* _end;       // last allocatable address + 1
-  HeapWord* _hard_end;  // _end + AlignmentReserve
-  bool      _retained;  // whether we hold a _retained_filler
-  MemRegion _retained_filler;
+  HeapWord* _end;           // Last allocatable address + 1
+  HeapWord* _hard_end;      // _end + AlignmentReserve
   // In support of ergonomic sizing of PLAB's
   size_t    _allocated;     // in HeapWord units
   size_t    _wasted;        // in HeapWord units
-  char tail[32];
-  static size_t FillerHeaderSize;
+  char      tail[32];
   static size_t AlignmentReserve;
 
-  // Flush the stats supporting ergonomic sizing of PLAB's
-  // Should not be called directly
-  void flush_stats(PLABStats* stats);
+  // Force future allocations to fail and queries for contains()
+  // to return false. Returns the amount of unused space in this PLAB.
+  size_t invalidate() {
+    _end    = _hard_end;
+    size_t remaining = pointer_delta(_end, _top);  // Calculate remaining space.
+    _top    = _end;      // Force future allocations to fail.
+    _bottom = _end;      // Force future contains() queries to return false.
+    return remaining;
+  }
+
+  // Fill in remaining space with a dummy object and invalidate the PLAB. Returns
+  // the amount of remaining space.
+  size_t retire_internal();
 
 public:
   // Initializes the buffer to be empty, but with the given "word_sz".
@@ -62,14 +68,10 @@
   ParGCAllocBuffer(size_t word_sz);
   virtual ~ParGCAllocBuffer() {}
 
-  static const size_t min_size() {
-    // Make sure that we return something that is larger than AlignmentReserve
-    return align_object_size(MAX2(MinTLABSize / HeapWordSize, (uintx)oopDesc::header_size())) + AlignmentReserve;
-  }
-
-  static const size_t max_size() {
-    return ThreadLocalAllocBuffer::max_size();
-  }
+  // Minimum PLAB size.
+  static size_t min_size();
+  // Maximum PLAB size.
+  static size_t max_size();
 
   // If an allocation of the given "word_sz" can be satisfied within the
   // buffer, do the allocation, returning a pointer to the start of the
@@ -128,62 +130,37 @@
     _allocated += word_sz();
   }
 
-  // Flush the stats supporting ergonomic sizing of PLAB's
-  // and retire the current buffer.
-  void flush_stats_and_retire(PLABStats* stats, bool end_of_gc, bool retain) {
-    // We flush the stats first in order to get a reading of
-    // unused space in the last buffer.
-    if (ResizePLAB) {
-      flush_stats(stats);
+  // Flush allocation statistics into the given PLABStats supporting ergonomic
+  // sizing of PLAB's and retire the current buffer. To be called at the end of
+  // GC.
+  void flush_and_retire_stats(PLABStats* stats);
 
-      // Since we have flushed the stats we need to clear
-      // the _allocated and _wasted fields. Not doing so
-      // will artifically inflate the values in the stats
-      // to which we add them.
-      // The next time we flush these values, we will add
-      // what we have just flushed in addition to the size
-      // of the buffers allocated between now and then.
-      _allocated = 0;
-      _wasted = 0;
-    }
-    // Retire the last allocation buffer.
-    retire(end_of_gc, retain);
-  }
-
-  // Force future allocations to fail and queries for contains()
-  // to return false
-  void invalidate() {
-    assert(!_retained, "Shouldn't retain an invalidated buffer.");
-    _end    = _hard_end;
-    _wasted += pointer_delta(_end, _top);  // unused  space
-    _top    = _end;      // force future allocations to fail
-    _bottom = _end;      // force future contains() queries to return false
-  }
-
-  // Fills in the unallocated portion of the buffer with a garbage object.
-  // If "end_of_gc" is TRUE, is after the last use in the GC.  IF "retain"
-  // is true, attempt to re-use the unused portion in the next GC.
-  virtual void retire(bool end_of_gc, bool retain);
+  // Fills in the unallocated portion of the buffer with a garbage object and updates
+  // statistics. To be called during GC.
+  virtual void retire();
 
   void print() PRODUCT_RETURN;
 };
 
-// PLAB stats book-keeping
+// PLAB book-keeping.
 class PLABStats VALUE_OBJ_CLASS_SPEC {
-  size_t _allocated;      // total allocated
+  size_t _allocated;      // Total allocated
   size_t _wasted;         // of which wasted (internal fragmentation)
   size_t _unused;         // Unused in last buffer
-  size_t _used;           // derived = allocated - wasted - unused
-  size_t _desired_plab_sz;// output of filter (below), suitably trimmed and quantized
+  size_t _desired_plab_sz;// Output of filter (below), suitably trimmed and quantized
   AdaptiveWeightedAverage
-         _filter;         // integrator with decay
+         _filter;         // Integrator with decay
 
+  void reset() {
+    _allocated = 0;
+    _wasted    = 0;
+    _unused    = 0;
+  }
  public:
   PLABStats(size_t desired_plab_sz_, unsigned wt) :
     _allocated(0),
     _wasted(0),
     _unused(0),
-    _used(0),
     _desired_plab_sz(desired_plab_sz_),
     _filter(wt)
   { }
@@ -200,9 +177,9 @@
     return _desired_plab_sz;
   }
 
+  // Updates the current desired PLAB size. Computes the new desired PLAB size,
+  // updates _desired_plab_sz and clears sensor accumulators.
   void adjust_desired_plab_sz(uint no_of_gc_workers);
-                                 // filter computation, latches output to
-                                 // _desired_plab_sz, clears sensor accumulators
 
   void add_allocated(size_t v) {
     Atomic::add_ptr(v, &_allocated);