# HG changeset patch
# User jmasa
# Date 1215641335 25200
# Node ID 12eea04c8b06285ebc5377d04f953bdeae235c09
# Parent  286bee59f34b26a633dab969f15cb01224646942
6672698: mangle_unused_area() should not remangle the entire heap at each collection.
Summary: Maintain a high water mark for the allocations in a space and mangle only up to that high water mark.
Reviewed-by: ysr, apetrusenko

diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/concurrentMarkSweep/binaryTreeDictionary.cpp
--- a/src/share/vm/gc_implementation/concurrentMarkSweep/binaryTreeDictionary.cpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/gc_implementation/concurrentMarkSweep/binaryTreeDictionary.cpp	Wed Jul 09 15:08:55 2008 -0700
@@ -71,8 +71,15 @@
 TreeList* TreeList::as_TreeList(HeapWord* addr, size_t size) {
   TreeChunk* tc = (TreeChunk*) addr;
   assert(size >= sizeof(TreeChunk), "Chunk is too small for a TreeChunk");
-  assert(tc->size() == 0 && tc->prev() == NULL && tc->next() == NULL,
-    "Space should be clear");
+  // The space in the heap will have been mangled initially but
+  // is not remangled when a free chunk is returned to the free list
+  // (since it is used to maintain the chunk on the free list).
+  assert((ZapUnusedHeapArea &&
+          SpaceMangler::is_mangled((HeapWord*) tc->size_addr()) &&
+          SpaceMangler::is_mangled((HeapWord*) tc->prev_addr()) &&
+          SpaceMangler::is_mangled((HeapWord*) tc->next_addr())) ||
+          (tc->size() == 0 && tc->prev() == NULL && tc->next() == NULL),
+    "Space should be clear or mangled");
   tc->setSize(size);
   tc->linkPrev(NULL);
   tc->linkNext(NULL);
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.cpp
--- a/src/share/vm/gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.cpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.cpp	Wed Jul 09 15:08:55 2008 -0700
@@ -54,7 +54,7 @@
   _collector(NULL)
 {
   _bt.set_space(this);
-  initialize(mr, true);
+  initialize(mr, SpaceDecorator::Clear, SpaceDecorator::Mangle);
   // We have all of "mr", all of which we place in the dictionary
   // as one big chunk. We'll need to decide here which of several
   // possible alternative dictionary implementations to use. For
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/concurrentMarkSweep/freeBlockDictionary.hpp
--- a/src/share/vm/gc_implementation/concurrentMarkSweep/freeBlockDictionary.hpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/gc_implementation/concurrentMarkSweep/freeBlockDictionary.hpp	Wed Jul 09 15:08:55 2008 -0700
@@ -22,7 +22,6 @@
  *
  */
 
-
 // A FreeBlockDictionary is an abstract superclass that will allow
 // a number of alternative implementations in the future.
 class FreeBlockDictionary: public CHeapObj {
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/concurrentMarkSweep/freeChunk.hpp
--- a/src/share/vm/gc_implementation/concurrentMarkSweep/freeChunk.hpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/gc_implementation/concurrentMarkSweep/freeChunk.hpp	Wed Jul 09 15:08:55 2008 -0700
@@ -85,6 +85,8 @@
   }
 
   debug_only(void* prev_addr() const { return (void*)&_prev; })
+  debug_only(void* next_addr() const { return (void*)&_next; })
+  debug_only(void* size_addr() const { return (void*)&_size; })
 
   size_t size() const volatile {
     LP64_ONLY(if (UseCompressedOops) return mark()->get_size(); else )
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/includeDB_gc_concurrentMarkSweep
--- a/src/share/vm/gc_implementation/includeDB_gc_concurrentMarkSweep	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/gc_implementation/includeDB_gc_concurrentMarkSweep	Wed Jul 09 15:08:55 2008 -0700
@@ -28,6 +28,7 @@
 binaryTreeDictionary.cpp                binaryTreeDictionary.hpp
 binaryTreeDictionary.cpp                globals.hpp
 binaryTreeDictionary.cpp                ostream.hpp
+binaryTreeDictionary.cpp                spaceDecorator.hpp
 
 binaryTreeDictionary.hpp                freeBlockDictionary.hpp
 binaryTreeDictionary.hpp                freeList.hpp
@@ -114,6 +115,7 @@
 compactibleFreeListSpace.cpp            liveRange.hpp
 compactibleFreeListSpace.cpp            oop.inline.hpp
 compactibleFreeListSpace.cpp            resourceArea.hpp
+compactibleFreeListSpace.cpp            spaceDecorator.hpp
 compactibleFreeListSpace.cpp            universe.inline.hpp
 compactibleFreeListSpace.cpp            vmThread.hpp
 
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/includeDB_gc_parNew
--- a/src/share/vm/gc_implementation/includeDB_gc_parNew	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/gc_implementation/includeDB_gc_parNew	Wed Jul 09 15:08:55 2008 -0700
@@ -22,16 +22,17 @@
 //
 //
 
-asParNewGeneration.hpp			adaptiveSizePolicy.hpp
-asParNewGeneration.hpp			parNewGeneration.hpp
+asParNewGeneration.hpp                  adaptiveSizePolicy.hpp
+asParNewGeneration.hpp                  parNewGeneration.hpp
 
-asParNewGeneration.cpp			asParNewGeneration.hpp
-asParNewGeneration.cpp			cmsAdaptiveSizePolicy.hpp
+asParNewGeneration.cpp                  asParNewGeneration.hpp
+asParNewGeneration.cpp                  cmsAdaptiveSizePolicy.hpp
 asParNewGeneration.cpp                  cmsGCAdaptivePolicyCounters.hpp
-asParNewGeneration.cpp			defNewGeneration.inline.hpp
-asParNewGeneration.cpp			oop.pcgc.inline.hpp
-asParNewGeneration.cpp			parNewGeneration.hpp
+asParNewGeneration.cpp                  defNewGeneration.inline.hpp
+asParNewGeneration.cpp                  oop.pcgc.inline.hpp
+asParNewGeneration.cpp                  parNewGeneration.hpp
 asParNewGeneration.cpp                  referencePolicy.hpp
+asParNewGeneration.cpp                  spaceDecorator.hpp
 
 parCardTableModRefBS.cpp                allocation.inline.hpp
 parCardTableModRefBS.cpp                cardTableModRefBS.hpp
@@ -75,6 +76,7 @@
 parNewGeneration.cpp                    resourceArea.hpp
 parNewGeneration.cpp                    sharedHeap.hpp
 parNewGeneration.cpp                    space.hpp
+parNewGeneration.cpp                    spaceDecorator.hpp
 parNewGeneration.cpp                    workgroup.hpp
 
 parNewGeneration.hpp                    defNewGeneration.hpp
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/includeDB_gc_parallelScavenge
--- a/src/share/vm/gc_implementation/includeDB_gc_parallelScavenge	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/gc_implementation/includeDB_gc_parallelScavenge	Wed Jul 09 15:08:55 2008 -0700
@@ -53,14 +53,15 @@
 asPSOldGen.cpp                          oop.inline.hpp
 asPSOldGen.cpp                          parallelScavengeHeap.hpp
 asPSOldGen.cpp                          psMarkSweepDecorator.hpp
-asPSOldGen.cpp				asPSOldGen.hpp
+asPSOldGen.cpp                          asPSOldGen.hpp
 
 asPSYoungGen.hpp                        generationCounters.hpp
 asPSYoungGen.hpp                        mutableSpace.hpp
 asPSYoungGen.hpp                        objectStartArray.hpp
 asPSYoungGen.hpp                        spaceCounters.hpp
 asPSYoungGen.hpp                        psVirtualspace.hpp
-asPSYoungGen.hpp			psYoungGen.hpp
+asPSYoungGen.hpp                        psYoungGen.hpp
+asPSYoungGen.hpp                        spaceDecorator.hpp
 
 asPSYoungGen.cpp                        gcUtil.hpp
 asPSYoungGen.cpp                        java.hpp
@@ -68,8 +69,9 @@
 asPSYoungGen.cpp                        parallelScavengeHeap.hpp
 asPSYoungGen.cpp                        psMarkSweepDecorator.hpp
 asPSYoungGen.cpp                        psScavenge.hpp
-asPSYoungGen.cpp			asPSYoungGen.hpp
-asPSYoungGen.cpp			psYoungGen.hpp
+asPSYoungGen.cpp                        asPSYoungGen.hpp
+asPSYoungGen.cpp                        psYoungGen.hpp
+asPSYoungGen.cpp                        spaceDecorator.hpp
 
 cardTableExtension.cpp                  cardTableExtension.hpp
 cardTableExtension.cpp                  gcTaskManager.hpp
@@ -225,6 +227,7 @@
 psMarkSweep.cpp                         referencePolicy.hpp
 psMarkSweep.cpp                         referenceProcessor.hpp
 psMarkSweep.cpp                         safepoint.hpp
+psMarkSweep.cpp                         spaceDecorator.hpp
 psMarkSweep.cpp                         symbolTable.hpp
 psMarkSweep.cpp                         systemDictionary.hpp
 psMarkSweep.cpp                         vmThread.hpp
@@ -239,6 +242,7 @@
 psMarkSweepDecorator.cpp                parallelScavengeHeap.hpp
 psMarkSweepDecorator.cpp                psMarkSweep.hpp
 psMarkSweepDecorator.cpp                psMarkSweepDecorator.hpp
+psMarkSweepDecorator.cpp                spaceDecorator.hpp
 psMarkSweepDecorator.cpp                systemDictionary.hpp
 
 psMarkSweepDecorator.hpp                mutableSpace.hpp
@@ -290,6 +294,7 @@
 psOldGen.cpp                            parallelScavengeHeap.hpp
 psOldGen.cpp                            psMarkSweepDecorator.hpp
 psOldGen.cpp                            psOldGen.hpp
+psOldGen.cpp                            spaceDecorator.hpp
 
 psOldGen.hpp                            psGenerationCounters.hpp
 psOldGen.hpp                            mutableSpace.hpp
@@ -351,6 +356,7 @@
 psScavenge.cpp                          referencePolicy.hpp
 psScavenge.cpp                          referenceProcessor.hpp
 psScavenge.cpp                          resourceArea.hpp
+psScavenge.cpp                          spaceDecorator.hpp
 psScavenge.cpp                          threadCritical.hpp
 psScavenge.cpp                          vmThread.hpp
 psScavenge.cpp                          vm_operations.hpp
@@ -409,8 +415,8 @@
 
 psVirtualspace.cpp			os.hpp
 psVirtualspace.cpp                      os_<os_family>.inline.hpp
-psVirtualspace.cpp			psVirtualspace.hpp
-psVirtualspace.cpp			virtualspace.hpp
+psVirtualspace.cpp                      psVirtualspace.hpp
+psVirtualspace.cpp                      virtualspace.hpp
 
 psYoungGen.cpp                          gcUtil.hpp
 psYoungGen.cpp                          java.hpp
@@ -419,7 +425,8 @@
 psYoungGen.cpp                          psMarkSweepDecorator.hpp
 psYoungGen.cpp                          psScavenge.hpp
 psYoungGen.cpp                          psYoungGen.hpp
-psYoungGen.cpp				mutableNUMASpace.hpp
+psYoungGen.cpp                          mutableNUMASpace.hpp
+psYoungGen.cpp                          spaceDecorator.hpp
 
 psYoungGen.hpp                          psGenerationCounters.hpp
 psYoungGen.hpp                          mutableSpace.hpp
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/includeDB_gc_shared
--- a/src/share/vm/gc_implementation/includeDB_gc_shared	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/gc_implementation/includeDB_gc_shared	Wed Jul 09 15:08:55 2008 -0700
@@ -56,6 +56,7 @@
 mutableNUMASpace.cpp                    mutableNUMASpace.hpp
 mutableNUMASpace.cpp                    oop.inline.hpp
 mutableNUMASpace.cpp                    sharedHeap.hpp
+mutableNUMASpace.cpp                    spaceDecorator.hpp
 mutableNUMASpace.cpp                    thread_<os_family>.inline.hpp
 
 mutableNUMASpace.hpp                    mutableSpace.hpp
@@ -64,6 +65,7 @@
 mutableSpace.cpp                        mutableSpace.hpp
 mutableSpace.cpp                        oop.inline.hpp
 mutableSpace.cpp                        safepoint.hpp
+mutableSpace.cpp                        spaceDecorator.hpp
 mutableSpace.cpp                        thread.hpp
 
 spaceCounters.cpp                       resourceArea.hpp
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/parNew/asParNewGeneration.cpp
--- a/src/share/vm/gc_implementation/parNew/asParNewGeneration.cpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/gc_implementation/parNew/asParNewGeneration.cpp	Wed Jul 09 15:08:55 2008 -0700
@@ -162,10 +162,9 @@
     // Grow the generation
     size_t change = desired_size - orig_size;
     assert(change % alignment == 0, "just checking");
-    if (!virtual_space()->expand_by(change)) {
+    if (expand(change)) {
       return false; // Error if we fail to resize!
     }
-
     size_changed = true;
   } else if (desired_size < orig_size) {
     size_t desired_change = orig_size - desired_size;
@@ -222,7 +221,9 @@
     // Was there a shrink of the survivor space?
     if (new_end < to()->end()) {
       MemRegion mr(to()->bottom(), new_end);
-      to()->initialize(mr, false /* clear */);
+      to()->initialize(mr,
+                       SpaceDecorator::DontClear,
+                       SpaceDecorator::DontMangle);
     }
   }
 }
@@ -322,9 +323,7 @@
                        pointer_delta(from_start, eden_start, sizeof(char)));
     }
 
-// tty->print_cr("eden_size before: " SIZE_FORMAT, eden_size);
     eden_size = align_size_down(eden_size, alignment);
-// tty->print_cr("eden_size after: " SIZE_FORMAT, eden_size);
     eden_end = eden_start + eden_size;
     assert(eden_end >= eden_start, "addition overflowed")
 
@@ -501,11 +500,31 @@
   size_t old_from = from()->capacity();
   size_t old_to   = to()->capacity();
 
+  // If not clearing the spaces, do some checking to verify that
+  // the spaces are already mangled.
+
+  // Must check mangling before the spaces are reshaped.  Otherwise,
+  // the bottom or end of one space may have moved into another
+  // a failure of the check may not correctly indicate which space
+  // is not properly mangled.
+  if (ZapUnusedHeapArea) {
+    HeapWord* limit = (HeapWord*) virtual_space()->high();
+    eden()->check_mangled_unused_area(limit);
+    from()->check_mangled_unused_area(limit);
+      to()->check_mangled_unused_area(limit);
+  }
+
   // The call to initialize NULL's the next compaction space
-  eden()->initialize(edenMR, true);
+  eden()->initialize(edenMR,
+                     SpaceDecorator::Clear,
+                     SpaceDecorator::DontMangle);
   eden()->set_next_compaction_space(from());
-    to()->initialize(toMR  , true);
-  from()->initialize(fromMR, false);     // Note, not cleared!
+    to()->initialize(toMR  ,
+                     SpaceDecorator::Clear,
+                     SpaceDecorator::DontMangle);
+  from()->initialize(fromMR,
+                     SpaceDecorator::DontClear,
+                     SpaceDecorator::DontMangle);
 
   assert(from()->top() == old_from_top, "from top changed!");
 
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/parNew/parNewGeneration.cpp
--- a/src/share/vm/gc_implementation/parNew/parNewGeneration.cpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/gc_implementation/parNew/parNewGeneration.cpp	Wed Jul 09 15:08:55 2008 -0700
@@ -727,7 +727,7 @@
   SpecializationStats::clear();
 
   age_table()->clear();
-  to()->clear();
+  to()->clear(SpaceDecorator::Mangle);
 
   gch->save_marks();
   assert(workers != NULL, "Need parallel worker threads.");
@@ -793,8 +793,18 @@
   }
   if (!promotion_failed()) {
     // Swap the survivor spaces.
-    eden()->clear();
-    from()->clear();
+    eden()->clear(SpaceDecorator::Mangle);
+    from()->clear(SpaceDecorator::Mangle);
+    if (ZapUnusedHeapArea) {
+      // This is now done here because of the piece-meal mangling which
+      // can check for valid mangling at intermediate points in the
+      // collection(s).  When a minor collection fails to collect
+      // sufficient space resizing of the young generation can occur
+      // an redistribute the spaces in the young generation.  Mangle
+      // here so that unzapped regions don't get distributed to
+      // other spaces.
+      to()->mangle_unused_area();
+    }
     swap_spaces();
 
     assert(to()->is_empty(), "to space should be empty now");
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/parallelScavenge/asPSYoungGen.cpp
--- a/src/share/vm/gc_implementation/parallelScavenge/asPSYoungGen.cpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/gc_implementation/parallelScavenge/asPSYoungGen.cpp	Wed Jul 09 15:08:55 2008 -0700
@@ -170,9 +170,20 @@
   if (desired_size > orig_size) {
     // Grow the generation
     size_t change = desired_size - orig_size;
+    HeapWord* prev_low = (HeapWord*) virtual_space()->low();
     if (!virtual_space()->expand_by(change)) {
       return false;
     }
+    if (ZapUnusedHeapArea) {
+      // Mangle newly committed space immediately because it
+      // can be done here more simply that after the new
+      // spaces have been computed.
+      HeapWord* new_low = (HeapWord*) virtual_space()->low();
+      assert(new_low < prev_low, "Did not grow");
+
+      MemRegion mangle_region(new_low, prev_low);
+      SpaceMangler::mangle_region(mangle_region);
+    }
     size_changed = true;
   } else if (desired_size < orig_size) {
     size_t desired_change = orig_size - desired_size;
@@ -215,8 +226,10 @@
 //  current implementation does not allow holes between the spaces
 //  _young_generation_boundary has to be reset because it changes.
 //  so additional verification
+
 void ASPSYoungGen::resize_spaces(size_t requested_eden_size,
                                  size_t requested_survivor_size) {
+  assert(UseAdaptiveSizePolicy, "sanity check");
   assert(requested_eden_size > 0 && requested_survivor_size > 0,
          "just checking");
 
@@ -276,22 +289,42 @@
 
   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
   const size_t alignment = heap->intra_heap_alignment();
+  const bool maintain_minimum =
+    (requested_eden_size + 2 * requested_survivor_size) <= min_gen_size();
 
+  bool eden_from_to_order = from_start < to_start;
   // Check whether from space is below to space
-  if (from_start < to_start) {
+  if (eden_from_to_order) {
     // Eden, from, to
+
     if (PrintAdaptiveSizePolicy && Verbose) {
       gclog_or_tty->print_cr("  Eden, from, to:");
     }
 
     // Set eden
-    // Compute how big eden can be, then adjust end.
-    // See comment in PSYoungGen::resize_spaces() on
-    // calculating eden_end.
-    const size_t eden_size = MIN2(requested_eden_size,
-                                  pointer_delta(from_start,
-                                                eden_start,
-                                                sizeof(char)));
+    // "requested_eden_size" is a goal for the size of eden
+    // and may not be attainable.  "eden_size" below is
+    // calculated based on the location of from-space and
+    // the goal for the size of eden.  from-space is
+    // fixed in place because it contains live data.
+    // The calculation is done this way to avoid 32bit
+    // overflow (i.e., eden_start + requested_eden_size
+    // may too large for representation in 32bits).
+    size_t eden_size;
+    if (maintain_minimum) {
+      // Only make eden larger than the requested size if
+      // the minimum size of the generation has to be maintained.
+      // This could be done in general but policy at a higher
+      // level is determining a requested size for eden and that
+      // should be honored unless there is a fundamental reason.
+      eden_size = pointer_delta(from_start,
+                                eden_start,
+                                sizeof(char));
+    } else {
+      eden_size = MIN2(requested_eden_size,
+                       pointer_delta(from_start, eden_start, sizeof(char)));
+    }
+
     eden_end = eden_start + eden_size;
     assert(eden_end >= eden_start, "addition overflowed")
 
@@ -371,12 +404,14 @@
     to_start = MAX2(to_start, eden_start + alignment);
 
     // Compute how big eden can be, then adjust end.
-    // See comment in PSYoungGen::resize_spaces() on
-    // calculating eden_end.
-    const size_t eden_size = MIN2(requested_eden_size,
-                                  pointer_delta(to_start,
-                                                eden_start,
-                                                sizeof(char)));
+    // See  comments above on calculating eden_end.
+    size_t eden_size;
+    if (maintain_minimum) {
+      eden_size = pointer_delta(to_start, eden_start, sizeof(char));
+    } else {
+      eden_size = MIN2(requested_eden_size,
+                       pointer_delta(to_start, eden_start, sizeof(char)));
+    }
     eden_end = eden_start + eden_size;
     assert(eden_end >= eden_start, "addition overflowed")
 
@@ -423,9 +458,47 @@
   size_t old_from = from_space()->capacity_in_bytes();
   size_t old_to   = to_space()->capacity_in_bytes();
 
-  eden_space()->initialize(edenMR, true);
-    to_space()->initialize(toMR  , true);
-  from_space()->initialize(fromMR, false);     // Note, not cleared!
+  if (ZapUnusedHeapArea) {
+    // NUMA is a special case because a numa space is not mangled
+    // in order to not prematurely bind its address to memory to
+    // the wrong memory (i.e., don't want the GC thread to first
+    // touch the memory).  The survivor spaces are not numa
+    // spaces and are mangled.
+    if (UseNUMA) {
+      if (eden_from_to_order) {
+        mangle_survivors(from_space(), fromMR, to_space(), toMR);
+      } else {
+        mangle_survivors(to_space(), toMR, from_space(), fromMR);
+      }
+    }
+
+    // If not mangling the spaces, do some checking to verify that
+    // the spaces are already mangled.
+    // The spaces should be correctly mangled at this point so
+    // do some checking here. Note that they are not being mangled
+    // in the calls to initialize().
+    // Must check mangling before the spaces are reshaped.  Otherwise,
+    // the bottom or end of one space may have moved into an area
+    // covered by another space and a failure of the check may
+    // not correctly indicate which space is not properly mangled.
+
+    HeapWord* limit = (HeapWord*) virtual_space()->high();
+    eden_space()->check_mangled_unused_area(limit);
+    from_space()->check_mangled_unused_area(limit);
+      to_space()->check_mangled_unused_area(limit);
+  }
+  // When an existing space is being initialized, it is not
+  // mangled because the space has been previously mangled.
+  eden_space()->initialize(edenMR,
+                           SpaceDecorator::Clear,
+                           SpaceDecorator::DontMangle);
+    to_space()->initialize(toMR,
+                           SpaceDecorator::Clear,
+                           SpaceDecorator::DontMangle);
+  from_space()->initialize(fromMR,
+                           SpaceDecorator::DontClear,
+                           SpaceDecorator::DontMangle);
+
   PSScavenge::set_young_generation_boundary(eden_space()->bottom());
 
   assert(from_space()->top() == old_from_top, "from top changed!");
@@ -446,7 +519,6 @@
   }
   space_invariants();
 }
-
 void ASPSYoungGen::reset_after_change() {
   assert_locked_or_safepoint(Heap_lock);
 
@@ -458,7 +530,9 @@
   HeapWord* eden_bottom = eden_space()->bottom();
   if (new_eden_bottom != eden_bottom) {
     MemRegion eden_mr(new_eden_bottom, eden_space()->end());
-    eden_space()->initialize(eden_mr, true);
+    eden_space()->initialize(eden_mr,
+                             SpaceDecorator::Clear,
+                             SpaceDecorator::Mangle);
     PSScavenge::set_young_generation_boundary(eden_space()->bottom());
   }
   MemRegion cmr((HeapWord*)virtual_space()->low(),
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/parallelScavenge/cardTableExtension.cpp
--- a/src/share/vm/gc_implementation/parallelScavenge/cardTableExtension.cpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/gc_implementation/parallelScavenge/cardTableExtension.cpp	Wed Jul 09 15:08:55 2008 -0700
@@ -666,9 +666,9 @@
 
     HeapWord* new_end_for_commit =
       MIN2(cur_committed.end(), _guard_region.start());
-    MemRegion new_committed =
-      MemRegion(new_start_aligned, new_end_for_commit);
-    if(!new_committed.is_empty()) {
+    if(new_start_aligned < new_end_for_commit) {
+      MemRegion new_committed =
+        MemRegion(new_start_aligned, new_end_for_commit);
       if (!os::commit_memory((char*)new_committed.start(),
                              new_committed.byte_size())) {
         vm_exit_out_of_memory(new_committed.byte_size(),
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/parallelScavenge/parallelScavengeHeap.cpp
--- a/src/share/vm/gc_implementation/parallelScavenge/parallelScavengeHeap.cpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/gc_implementation/parallelScavenge/parallelScavengeHeap.cpp	Wed Jul 09 15:08:55 2008 -0700
@@ -938,3 +938,23 @@
   // Delegate the resize to the generation.
   _old_gen->resize(desired_free_space);
 }
+
+#ifndef PRODUCT
+void ParallelScavengeHeap::record_gen_tops_before_GC() {
+  if (ZapUnusedHeapArea) {
+    young_gen()->record_spaces_top();
+    old_gen()->record_spaces_top();
+    perm_gen()->record_spaces_top();
+  }
+}
+
+void ParallelScavengeHeap::gen_mangle_unused_area() {
+  if (ZapUnusedHeapArea) {
+    young_gen()->eden_space()->mangle_unused_area();
+    young_gen()->to_space()->mangle_unused_area();
+    young_gen()->from_space()->mangle_unused_area();
+    old_gen()->object_space()->mangle_unused_area();
+    perm_gen()->object_space()->mangle_unused_area();
+  }
+}
+#endif
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/parallelScavenge/parallelScavengeHeap.hpp
--- a/src/share/vm/gc_implementation/parallelScavenge/parallelScavengeHeap.hpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/gc_implementation/parallelScavenge/parallelScavengeHeap.hpp	Wed Jul 09 15:08:55 2008 -0700
@@ -213,6 +213,12 @@
   // Resize the old generation.  The reserved space for the
   // generation may be expanded in preparation for the resize.
   void resize_old_gen(size_t desired_free_space);
+
+  // Save the tops of the spaces in all generations
+  void record_gen_tops_before_GC() PRODUCT_RETURN;
+
+  // Mangle the unused parts of all spaces in the heap
+  void gen_mangle_unused_area() PRODUCT_RETURN;
 };
 
 inline size_t ParallelScavengeHeap::set_alignment(size_t& var, size_t val)
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/parallelScavenge/psMarkSweep.cpp
--- a/src/share/vm/gc_implementation/parallelScavenge/psMarkSweep.cpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/gc_implementation/parallelScavenge/psMarkSweep.cpp	Wed Jul 09 15:08:55 2008 -0700
@@ -98,6 +98,9 @@
   // Increment the invocation count
   heap->increment_total_collections(true /* full */);
 
+  // Save information needed to minimize mangling
+  heap->record_gen_tops_before_GC();
+
   // We need to track unique mark sweep invocations as well.
   _total_invocations++;
 
@@ -188,6 +191,12 @@
 
     deallocate_stacks();
 
+    if (ZapUnusedHeapArea) {
+      // Do a complete mangle (top to end) because the usage for
+      // scratch does not maintain a top pointer.
+      young_gen->to_space()->mangle_unused_area_complete();
+    }
+
     eden_empty = young_gen->eden_space()->is_empty();
     if (!eden_empty) {
       eden_empty = absorb_live_data_from_eden(size_policy, young_gen, old_gen);
@@ -198,7 +207,7 @@
     Universe::update_heap_info_at_gc();
 
     survivors_empty = young_gen->from_space()->is_empty() &&
-      young_gen->to_space()->is_empty();
+                      young_gen->to_space()->is_empty();
     young_gen_empty = eden_empty && survivors_empty;
 
     BarrierSet* bs = heap->barrier_set();
@@ -344,6 +353,11 @@
     perm_gen->verify_object_start_array();
   }
 
+  if (ZapUnusedHeapArea) {
+    old_gen->object_space()->check_mangled_unused_area_complete();
+    perm_gen->object_space()->check_mangled_unused_area_complete();
+  }
+
   NOT_PRODUCT(ref_processor()->verify_no_references_recorded());
 
   if (PrintHeapAtGC) {
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/parallelScavenge/psMarkSweepDecorator.cpp
--- a/src/share/vm/gc_implementation/parallelScavenge/psMarkSweepDecorator.cpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/gc_implementation/parallelScavenge/psMarkSweepDecorator.cpp	Wed Jul 09 15:08:55 2008 -0700
@@ -438,5 +438,7 @@
          "should point inside space");
   space()->set_top(compaction_top());
 
-  if (mangle_free_space) space()->mangle_unused_area();
+  if (mangle_free_space) {
+    space()->mangle_unused_area();
+  }
 }
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/parallelScavenge/psOldGen.cpp
--- a/src/share/vm/gc_implementation/parallelScavenge/psOldGen.cpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/gc_implementation/parallelScavenge/psOldGen.cpp	Wed Jul 09 15:08:55 2008 -0700
@@ -87,6 +87,15 @@
 
   MemRegion cmr((HeapWord*)virtual_space()->low(),
                 (HeapWord*)virtual_space()->high());
+  if (ZapUnusedHeapArea) {
+    // Mangle newly committed space immediately rather than
+    // waiting for the initialization of the space even though
+    // mangling is related to spaces.  Doing it here eliminates
+    // the need to carry along information that a complete mangling
+    // (bottom to end) needs to be done.
+    SpaceMangler::mangle_region(cmr);
+  }
+
   Universe::heap()->barrier_set()->resize_covered_region(cmr);
 
   CardTableModRefBS* _ct = (CardTableModRefBS*)Universe::heap()->barrier_set();
@@ -112,7 +121,9 @@
   if (_object_space == NULL)
     vm_exit_during_initialization("Could not allocate an old gen space");
 
-  object_space()->initialize(cmr, true);
+  object_space()->initialize(cmr,
+                             SpaceDecorator::Clear,
+                             SpaceDecorator::Mangle);
 
   _object_mark_sweep = new PSMarkSweepDecorator(_object_space, start_array(), MarkSweepDeadRatio);
 
@@ -232,6 +243,19 @@
   assert_locked_or_safepoint(Heap_lock);
   bool result = virtual_space()->expand_by(bytes);
   if (result) {
+    if (ZapUnusedHeapArea) {
+      // We need to mangle the newly expanded area. The memregion spans
+      // end -> new_end, we assume that top -> end is already mangled.
+      // Do the mangling before post_resize() is called because
+      // the space is available for allocation after post_resize();
+      HeapWord* const virtual_space_high = (HeapWord*) virtual_space()->high();
+      assert(object_space()->end() < virtual_space_high,
+        "Should be true before post_resize()");
+      MemRegion mangle_region(object_space()->end(), virtual_space_high);
+      // Note that the object space has not yet been updated to
+      // coincede with the new underlying virtual space.
+      SpaceMangler::mangle_region(mangle_region);
+    }
     post_resize();
     if (UsePerfData) {
       _space_counters->update_capacity();
@@ -348,16 +372,7 @@
   start_array()->set_covered_region(new_memregion);
   Universe::heap()->barrier_set()->resize_covered_region(new_memregion);
 
-  // Did we expand?
   HeapWord* const virtual_space_high = (HeapWord*) virtual_space()->high();
-  if (object_space()->end() < virtual_space_high) {
-    // We need to mangle the newly expanded area. The memregion spans
-    // end -> new_end, we assume that top -> end is already mangled.
-    // This cannot be safely tested for, as allocation may be taking
-    // place.
-    MemRegion mangle_region(object_space()->end(), virtual_space_high);
-    object_space()->mangle_region(mangle_region);
-  }
 
   // ALWAYS do this last!!
   object_space()->set_end(virtual_space_high);
@@ -462,3 +477,10 @@
   VerifyObjectStartArrayClosure check( this, &_start_array );
   object_iterate(&check);
 }
+
+#ifndef PRODUCT
+void PSOldGen::record_spaces_top() {
+  assert(ZapUnusedHeapArea, "Not mangling unused space");
+  object_space()->set_top_for_allocations();
+}
+#endif
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/parallelScavenge/psOldGen.hpp
--- a/src/share/vm/gc_implementation/parallelScavenge/psOldGen.hpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/gc_implementation/parallelScavenge/psOldGen.hpp	Wed Jul 09 15:08:55 2008 -0700
@@ -185,4 +185,8 @@
 
   // Printing support
   virtual const char* name() const { return _name; }
+
+  // Debugging support
+  // Save the tops of all spaces for later use during mangling.
+  void record_spaces_top() PRODUCT_RETURN;
 };
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/parallelScavenge/psParallelCompact.cpp
--- a/src/share/vm/gc_implementation/parallelScavenge/psParallelCompact.cpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/gc_implementation/parallelScavenge/psParallelCompact.cpp	Wed Jul 09 15:08:55 2008 -0700
@@ -1058,6 +1058,10 @@
 
   ref_processor()->enqueue_discovered_references(NULL);
 
+  if (ZapUnusedHeapArea) {
+    heap->gen_mangle_unused_area();
+  }
+
   // Update time of last GC
   reset_millis_since_last_gc();
 }
@@ -1959,6 +1963,11 @@
   PSPermGen* perm_gen = heap->perm_gen();
   PSAdaptiveSizePolicy* size_policy = heap->size_policy();
 
+  if (ZapUnusedHeapArea) {
+    // Save information needed to minimize mangling
+    heap->record_gen_tops_before_GC();
+  }
+
   _print_phases = PrintGCDetails && PrintParallelOldGCPhaseTimes;
 
   // Make sure data structures are sane, make the heap parsable, and do other
@@ -2127,17 +2136,19 @@
         size_t max_eden_size = young_gen->max_size() -
           young_gen->from_space()->capacity_in_bytes() -
           young_gen->to_space()->capacity_in_bytes();
-        size_policy->compute_generation_free_space(young_gen->used_in_bytes(),
-                                 young_gen->eden_space()->used_in_bytes(),
-                                 old_gen->used_in_bytes(),
-                                 perm_gen->used_in_bytes(),
-                                 young_gen->eden_space()->capacity_in_bytes(),
-                                 old_gen->max_gen_size(),
-                                 max_eden_size,
-                                 true /* full gc*/,
-                                 gc_cause);
-
-        heap->resize_old_gen(size_policy->calculated_old_free_size_in_bytes());
+        size_policy->compute_generation_free_space(
+                              young_gen->used_in_bytes(),
+                              young_gen->eden_space()->used_in_bytes(),
+                              old_gen->used_in_bytes(),
+                              perm_gen->used_in_bytes(),
+                              young_gen->eden_space()->capacity_in_bytes(),
+                              old_gen->max_gen_size(),
+                              max_eden_size,
+                              true /* full gc*/,
+                              gc_cause);
+
+        heap->resize_old_gen(
+          size_policy->calculated_old_free_size_in_bytes());
 
         // Don't resize the young generation at an major collection.  A
         // desired young generation size may have been calculated but
@@ -2210,6 +2221,11 @@
     perm_gen->verify_object_start_array();
   }
 
+  if (ZapUnusedHeapArea) {
+    old_gen->object_space()->check_mangled_unused_area_complete();
+    perm_gen->object_space()->check_mangled_unused_area_complete();
+  }
+
   NOT_PRODUCT(ref_processor()->verify_no_references_recorded());
 
   collection_exit.update();
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/parallelScavenge/psParallelCompact.hpp
--- a/src/share/vm/gc_implementation/parallelScavenge/psParallelCompact.hpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/gc_implementation/parallelScavenge/psParallelCompact.hpp	Wed Jul 09 15:08:55 2008 -0700
@@ -716,6 +716,99 @@
   virtual IterationStatus do_addr(HeapWord* addr, size_t words);
 };
 
+// The UseParallelOldGC collector is a stop-the-world garbage
+// collector that does parts of the collection using parallel threads.
+// The collection includes the tenured generation and the young
+// generation.  The permanent generation is collected at the same
+// time as the other two generations but the permanent generation
+// is collect by a single GC thread.  The permanent generation is
+// collected serially because of the requirement that during the
+// processing of a klass AAA, any objects reference by AAA must
+// already have been processed.  This requirement is enforced by
+// a left (lower address) to right (higher address) sliding compaction.
+//
+// There are four phases of the collection.
+//
+//      - marking phase
+//      - summary phase
+//      - compacting phase
+//      - clean up phase
+//
+// Roughly speaking these phases correspond, respectively, to
+//      - mark all the live objects
+//      - calculate the destination of each object at the end of the collection
+//      - move the objects to their destination
+//      - update some references and reinitialize some variables
+//
+// These three phases are invoked in PSParallelCompact::invoke_no_policy().
+// The marking phase is implemented in PSParallelCompact::marking_phase()
+// and does a complete marking of the heap.
+// The summary phase is implemented in PSParallelCompact::summary_phase().
+// The move and update phase is implemented in PSParallelCompact::compact().
+//
+// A space that is being collected is divided into chunks and with
+// each chunk is associated an object of type ParallelCompactData.
+// Each chunk is of a fixed size and typically will contain more than
+// 1 object and may have parts of objects at the front and back of the
+// chunk.
+//
+// chunk            -----+---------------------+----------
+// objects covered   [ AAA  )[ BBB )[ CCC   )[ DDD     )
+//
+// The marking phase does a complete marking of all live objects in the
+// heap.  The marking also compiles the size of the data for
+// all live objects covered by the chunk.  This size includes the
+// part of any live object spanning onto the chunk (part of AAA
+// if it is live) from the front, all live objects contained in the chunk
+// (BBB and/or CCC if they are live), and the part of any live objects
+// covered by the chunk that extends off the chunk (part of DDD if it is
+// live).  The marking phase uses multiple GC threads and marking is
+// done in a bit array of type ParMarkBitMap.  The marking of the
+// bit map is done atomically as is the accumulation of the size of the
+// live objects covered by a chunk.
+//
+// The summary phase calculates the total live data to the left of
+// each chunk XXX.  Based on that total and the bottom of the space,
+// it can calculate the starting location of the live data in XXX.
+// The summary phase calculates for each chunk XXX quantites such as
+//
+//      - the amount of live data at the beginning of a chunk from an object
+//      entering the chunk.
+//      - the location of the first live data on the chunk
+//      - a count of the number of chunks receiving live data from XXX.
+//
+// See ParallelCompactData for precise details.  The summary phase also
+// calculates the dense prefix for the compaction.  The dense prefix
+// is a portion at the beginning of the space that is not moved.  The
+// objects in the dense prefix do need to have their object references
+// updated.  See method summarize_dense_prefix().
+//
+// The summary phase is done using 1 GC thread.
+//
+// The compaction phase moves objects to their new location and updates
+// all references in the object.
+//
+// A current exception is that objects that cross a chunk boundary
+// are moved but do not have their references updated.  References are
+// not updated because it cannot easily be determined if the klass
+// pointer KKK for the object AAA has been updated.  KKK likely resides
+// in a chunk to the left of the chunk containing AAA.  These AAA's
+// have there references updated at the end in a clean up phase.
+// See the method PSParallelCompact::update_deferred_objects().  An
+// alternate strategy is being investigated for this deferral of updating.
+//
+// Compaction is done on a chunk basis.  A chunk that is ready to be
+// filled is put on a ready list and GC threads take chunk off the list
+// and fill them.  A chunk is ready to be filled if it
+// empty of live objects.  Such a chunk may have been initially
+// empty (only contained
+// dead objects) or may have had all its live objects copied out already.
+// A chunk that compacts into itself is also ready for filling.  The
+// ready list is initially filled with empty chunks and chunks compacting
+// into themselves.  There is always at least 1 chunk that can be put on
+// the ready list.  The chunks are atomically added and removed from
+// the ready list.
+//
 class PSParallelCompact : AllStatic {
  public:
   // Convenient access to type names.
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/parallelScavenge/psScavenge.cpp
--- a/src/share/vm/gc_implementation/parallelScavenge/psScavenge.cpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/gc_implementation/parallelScavenge/psScavenge.cpp	Wed Jul 09 15:08:55 2008 -0700
@@ -265,6 +265,11 @@
     young_gen->eden_space()->accumulate_statistics();
   }
 
+  if (ZapUnusedHeapArea) {
+    // Save information needed to minimize mangling
+    heap->record_gen_tops_before_GC();
+  }
+
   if (PrintHeapAtGC) {
     Universe::print_heap_before_gc();
   }
@@ -315,7 +320,7 @@
     if (!ScavengeWithObjectsInToSpace) {
       assert(young_gen->to_space()->is_empty(),
              "Attempt to scavenge with live objects in to_space");
-      young_gen->to_space()->clear();
+      young_gen->to_space()->clear(SpaceDecorator::Mangle);
     } else if (ZapUnusedHeapArea) {
       young_gen->to_space()->mangle_unused_area();
     }
@@ -437,8 +442,10 @@
 
     if (!promotion_failure_occurred) {
       // Swap the survivor spaces.
-      young_gen->eden_space()->clear();
-      young_gen->from_space()->clear();
+
+
+      young_gen->eden_space()->clear(SpaceDecorator::Mangle);
+      young_gen->from_space()->clear(SpaceDecorator::Mangle);
       young_gen->swap_spaces();
 
       size_t survived = young_gen->from_space()->used_in_bytes();
@@ -600,6 +607,12 @@
     Universe::print_heap_after_gc();
   }
 
+  if (ZapUnusedHeapArea) {
+    young_gen->eden_space()->check_mangled_unused_area_complete();
+    young_gen->from_space()->check_mangled_unused_area_complete();
+    young_gen->to_space()->check_mangled_unused_area_complete();
+  }
+
   scavenge_exit.update();
 
   if (PrintGCTaskTimeStamps) {
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/parallelScavenge/psYoungGen.cpp
--- a/src/share/vm/gc_implementation/parallelScavenge/psYoungGen.cpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/gc_implementation/parallelScavenge/psYoungGen.cpp	Wed Jul 09 15:08:55 2008 -0700
@@ -36,7 +36,7 @@
 void PSYoungGen::initialize_virtual_space(ReservedSpace rs, size_t alignment) {
   assert(_init_gen_size != 0, "Should have a finite size");
   _virtual_space = new PSVirtualSpace(rs, alignment);
-  if (!_virtual_space->expand_by(_init_gen_size)) {
+  if (!virtual_space()->expand_by(_init_gen_size)) {
     vm_exit_during_initialization("Could not reserve enough space for "
                                   "object heap");
   }
@@ -49,12 +49,19 @@
 
 void PSYoungGen::initialize_work() {
 
-  _reserved = MemRegion((HeapWord*)_virtual_space->low_boundary(),
-                        (HeapWord*)_virtual_space->high_boundary());
+  _reserved = MemRegion((HeapWord*)virtual_space()->low_boundary(),
+                        (HeapWord*)virtual_space()->high_boundary());
+
+  MemRegion cmr((HeapWord*)virtual_space()->low(),
+                (HeapWord*)virtual_space()->high());
+  Universe::heap()->barrier_set()->resize_covered_region(cmr);
 
-  MemRegion cmr((HeapWord*)_virtual_space->low(),
-                (HeapWord*)_virtual_space->high());
-  Universe::heap()->barrier_set()->resize_covered_region(cmr);
+  if (ZapUnusedHeapArea) {
+    // Mangle newly committed space immediately because it
+    // can be done here more simply that after the new
+    // spaces have been computed.
+    SpaceMangler::mangle_region(cmr);
+  }
 
   if (UseNUMA) {
     _eden_space = new MutableNUMASpace();
@@ -89,7 +96,7 @@
   // Compute maximum space sizes for performance counters
   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
   size_t alignment = heap->intra_heap_alignment();
-  size_t size = _virtual_space->reserved_size();
+  size_t size = virtual_space()->reserved_size();
 
   size_t max_survivor_size;
   size_t max_eden_size;
@@ -142,7 +149,7 @@
 
   // Compute sizes
   size_t alignment = heap->intra_heap_alignment();
-  size_t size = _virtual_space->committed_size();
+  size_t size = virtual_space()->committed_size();
 
   size_t survivor_size = size / InitialSurvivorRatio;
   survivor_size = align_size_down(survivor_size, alignment);
@@ -164,18 +171,18 @@
 }
 
 void PSYoungGen::set_space_boundaries(size_t eden_size, size_t survivor_size) {
-  assert(eden_size < _virtual_space->committed_size(), "just checking");
+  assert(eden_size < virtual_space()->committed_size(), "just checking");
   assert(eden_size > 0  && survivor_size > 0, "just checking");
 
   // Initial layout is Eden, to, from. After swapping survivor spaces,
   // that leaves us with Eden, from, to, which is step one in our two
   // step resize-with-live-data procedure.
-  char *eden_start = _virtual_space->low();
+  char *eden_start = virtual_space()->low();
   char *to_start   = eden_start + eden_size;
   char *from_start = to_start   + survivor_size;
   char *from_end   = from_start + survivor_size;
 
-  assert(from_end == _virtual_space->high(), "just checking");
+  assert(from_end == virtual_space()->high(), "just checking");
   assert(is_object_aligned((intptr_t)eden_start), "checking alignment");
   assert(is_object_aligned((intptr_t)to_start),   "checking alignment");
   assert(is_object_aligned((intptr_t)from_start), "checking alignment");
@@ -184,9 +191,9 @@
   MemRegion to_mr  ((HeapWord*)to_start, (HeapWord*)from_start);
   MemRegion from_mr((HeapWord*)from_start, (HeapWord*)from_end);
 
-  eden_space()->initialize(eden_mr, true);
-    to_space()->initialize(to_mr  , true);
-  from_space()->initialize(from_mr, true);
+  eden_space()->initialize(eden_mr, true, ZapUnusedHeapArea);
+    to_space()->initialize(to_mr  , true, ZapUnusedHeapArea);
+  from_space()->initialize(from_mr, true, ZapUnusedHeapArea);
 }
 
 #ifndef PRODUCT
@@ -207,7 +214,7 @@
   char* to_start   = (char*)to_space()->bottom();
   char* to_end     = (char*)to_space()->end();
 
-  guarantee(eden_start >= _virtual_space->low(), "eden bottom");
+  guarantee(eden_start >= virtual_space()->low(), "eden bottom");
   guarantee(eden_start < eden_end, "eden space consistency");
   guarantee(from_start < from_end, "from space consistency");
   guarantee(to_start < to_end, "to space consistency");
@@ -217,29 +224,29 @@
     // Eden, from, to
     guarantee(eden_end <= from_start, "eden/from boundary");
     guarantee(from_end <= to_start,   "from/to boundary");
-    guarantee(to_end <= _virtual_space->high(), "to end");
+    guarantee(to_end <= virtual_space()->high(), "to end");
   } else {
     // Eden, to, from
     guarantee(eden_end <= to_start, "eden/to boundary");
     guarantee(to_end <= from_start, "to/from boundary");
-    guarantee(from_end <= _virtual_space->high(), "from end");
+    guarantee(from_end <= virtual_space()->high(), "from end");
   }
 
   // More checks that the virtual space is consistent with the spaces
-  assert(_virtual_space->committed_size() >=
+  assert(virtual_space()->committed_size() >=
     (eden_space()->capacity_in_bytes() +
      to_space()->capacity_in_bytes() +
      from_space()->capacity_in_bytes()), "Committed size is inconsistent");
-  assert(_virtual_space->committed_size() <= _virtual_space->reserved_size(),
+  assert(virtual_space()->committed_size() <= virtual_space()->reserved_size(),
     "Space invariant");
   char* eden_top = (char*)eden_space()->top();
   char* from_top = (char*)from_space()->top();
   char* to_top = (char*)to_space()->top();
-  assert(eden_top <= _virtual_space->high(), "eden top");
-  assert(from_top <= _virtual_space->high(), "from top");
-  assert(to_top <= _virtual_space->high(), "to top");
+  assert(eden_top <= virtual_space()->high(), "eden top");
+  assert(from_top <= virtual_space()->high(), "from top");
+  assert(to_top <= virtual_space()->high(), "to top");
 
-  _virtual_space->verify();
+  virtual_space()->verify();
 }
 #endif
 
@@ -265,8 +272,8 @@
 
 
 bool PSYoungGen::resize_generation(size_t eden_size, size_t survivor_size) {
-  const size_t alignment = _virtual_space->alignment();
-  size_t orig_size = _virtual_space->committed_size();
+  const size_t alignment = virtual_space()->alignment();
+  size_t orig_size = virtual_space()->committed_size();
   bool size_changed = false;
 
   // There used to be this guarantee there.
@@ -288,10 +295,18 @@
     // Grow the generation
     size_t change = desired_size - orig_size;
     assert(change % alignment == 0, "just checking");
-    if (!_virtual_space->expand_by(change)) {
+    HeapWord* prev_high = (HeapWord*) virtual_space()->high();
+    if (!virtual_space()->expand_by(change)) {
       return false; // Error if we fail to resize!
     }
-
+    if (ZapUnusedHeapArea) {
+      // Mangle newly committed space immediately because it
+      // can be done here more simply that after the new
+      // spaces have been computed.
+      HeapWord* new_high = (HeapWord*) virtual_space()->high();
+      MemRegion mangle_region(prev_high, new_high);
+      SpaceMangler::mangle_region(mangle_region);
+    }
     size_changed = true;
   } else if (desired_size < orig_size) {
     size_t desired_change = orig_size - desired_size;
@@ -321,19 +336,95 @@
     post_resize();
 
     if (Verbose && PrintGC) {
-      size_t current_size  = _virtual_space->committed_size();
+      size_t current_size  = virtual_space()->committed_size();
       gclog_or_tty->print_cr("PSYoung generation size changed: "
                              SIZE_FORMAT "K->" SIZE_FORMAT "K",
                              orig_size/K, current_size/K);
     }
   }
 
-  guarantee(eden_plus_survivors <= _virtual_space->committed_size() ||
-            _virtual_space->committed_size() == max_size(), "Sanity");
+  guarantee(eden_plus_survivors <= virtual_space()->committed_size() ||
+            virtual_space()->committed_size() == max_size(), "Sanity");
 
   return true;
 }
 
+#ifndef PRODUCT
+// In the numa case eden is not mangled so a survivor space
+// moving into a region previously occupied by a survivor
+// may find an unmangled region.  Also in the PS case eden
+// to-space and from-space may not touch (i.e., there may be
+// gaps between them due to movement while resizing the
+// spaces).  Those gaps must be mangled.
+void PSYoungGen::mangle_survivors(MutableSpace* s1,
+                                  MemRegion s1MR,
+                                  MutableSpace* s2,
+                                  MemRegion s2MR) {
+  // Check eden and gap between eden and from-space, in deciding
+  // what to mangle in from-space.  Check the gap between from-space
+  // and to-space when deciding what to mangle.
+  //
+  //      +--------+   +----+    +---+
+  //      | eden   |   |s1  |    |s2 |
+  //      +--------+   +----+    +---+
+  //                 +-------+ +-----+
+  //                 |s1MR   | |s2MR |
+  //                 +-------+ +-----+
+  // All of survivor-space is properly mangled so find the
+  // upper bound on the mangling for any portion above current s1.
+  HeapWord* delta_end = MIN2(s1->bottom(), s1MR.end());
+  MemRegion delta1_left;
+  if (s1MR.start() < delta_end) {
+    delta1_left = MemRegion(s1MR.start(), delta_end);
+    s1->mangle_region(delta1_left);
+  }
+  // Find any portion to the right of the current s1.
+  HeapWord* delta_start = MAX2(s1->end(), s1MR.start());
+  MemRegion delta1_right;
+  if (delta_start < s1MR.end()) {
+    delta1_right = MemRegion(delta_start, s1MR.end());
+    s1->mangle_region(delta1_right);
+  }
+
+  // Similarly for the second survivor space except that
+  // any of the new region that overlaps with the current
+  // region of the first survivor space has already been
+  // mangled.
+  delta_end = MIN2(s2->bottom(), s2MR.end());
+  delta_start = MAX2(s2MR.start(), s1->end());
+  MemRegion delta2_left;
+  if (s2MR.start() < delta_end) {
+    delta2_left = MemRegion(s2MR.start(), delta_end);
+    s2->mangle_region(delta2_left);
+  }
+  delta_start = MAX2(s2->end(), s2MR.start());
+  MemRegion delta2_right;
+  if (delta_start < s2MR.end()) {
+    s2->mangle_region(delta2_right);
+  }
+
+  if (TraceZapUnusedHeapArea) {
+    // s1
+    gclog_or_tty->print_cr("Current region: [" PTR_FORMAT ", " PTR_FORMAT ") "
+      "New region: [" PTR_FORMAT ", " PTR_FORMAT ")",
+      s1->bottom(), s1->end(), s1MR.start(), s1MR.end());
+    gclog_or_tty->print_cr("    Mangle before: [" PTR_FORMAT ", "
+      PTR_FORMAT ")  Mangle after: [" PTR_FORMAT ", " PTR_FORMAT ")",
+      delta1_left.start(), delta1_left.end(), delta1_right.start(),
+      delta1_right.end());
+
+    // s2
+    gclog_or_tty->print_cr("Current region: [" PTR_FORMAT ", " PTR_FORMAT ") "
+      "New region: [" PTR_FORMAT ", " PTR_FORMAT ")",
+      s2->bottom(), s2->end(), s2MR.start(), s2MR.end());
+    gclog_or_tty->print_cr("    Mangle before: [" PTR_FORMAT ", "
+      PTR_FORMAT ")  Mangle after: [" PTR_FORMAT ", " PTR_FORMAT ")",
+      delta2_left.start(), delta2_left.end(), delta2_right.start(),
+      delta2_right.end());
+  }
+
+}
+#endif // NOT PRODUCT
 
 void PSYoungGen::resize_spaces(size_t requested_eden_size,
                                size_t requested_survivor_size) {
@@ -396,9 +487,11 @@
   const bool maintain_minimum =
     (requested_eden_size + 2 * requested_survivor_size) <= min_gen_size();
 
+  bool eden_from_to_order = from_start < to_start;
   // Check whether from space is below to space
-  if (from_start < to_start) {
+  if (eden_from_to_order) {
     // Eden, from, to
+    eden_from_to_order = true;
     if (PrintAdaptiveSizePolicy && Verbose) {
       gclog_or_tty->print_cr("  Eden, from, to:");
     }
@@ -435,7 +528,7 @@
     // extra calculations.
 
     // First calculate an optimal to-space
-    to_end   = (char*)_virtual_space->high();
+    to_end   = (char*)virtual_space()->high();
     to_start = (char*)pointer_delta(to_end, (char*)requested_survivor_size,
                                     sizeof(char));
 
@@ -491,7 +584,7 @@
     // to space as if we were able to resize from space, even though from
     // space is not modified.
     // Giving eden priority was tried and gave poorer performance.
-    to_end   = (char*)pointer_delta(_virtual_space->high(),
+    to_end   = (char*)pointer_delta(virtual_space()->high(),
                                     (char*)requested_survivor_size,
                                     sizeof(char));
     to_end   = MIN2(to_end, from_start);
@@ -560,9 +653,45 @@
   size_t old_from = from_space()->capacity_in_bytes();
   size_t old_to   = to_space()->capacity_in_bytes();
 
-  eden_space()->initialize(edenMR, true);
-    to_space()->initialize(toMR  , true);
-  from_space()->initialize(fromMR, false);     // Note, not cleared!
+  if (ZapUnusedHeapArea) {
+    // NUMA is a special case because a numa space is not mangled
+    // in order to not prematurely bind its address to memory to
+    // the wrong memory (i.e., don't want the GC thread to first
+    // touch the memory).  The survivor spaces are not numa
+    // spaces and are mangled.
+    if (UseNUMA) {
+      if (eden_from_to_order) {
+        mangle_survivors(from_space(), fromMR, to_space(), toMR);
+      } else {
+        mangle_survivors(to_space(), toMR, from_space(), fromMR);
+      }
+    }
+
+    // If not mangling the spaces, do some checking to verify that
+    // the spaces are already mangled.
+    // The spaces should be correctly mangled at this point so
+    // do some checking here. Note that they are not being mangled
+    // in the calls to initialize().
+    // Must check mangling before the spaces are reshaped.  Otherwise,
+    // the bottom or end of one space may have moved into an area
+    // covered by another space and a failure of the check may
+    // not correctly indicate which space is not properly mangled.
+    HeapWord* limit = (HeapWord*) virtual_space()->high();
+    eden_space()->check_mangled_unused_area(limit);
+    from_space()->check_mangled_unused_area(limit);
+      to_space()->check_mangled_unused_area(limit);
+  }
+  // When an existing space is being initialized, it is not
+  // mangled because the space has been previously mangled.
+  eden_space()->initialize(edenMR,
+                           SpaceDecorator::Clear,
+                           SpaceDecorator::DontMangle);
+    to_space()->initialize(toMR,
+                           SpaceDecorator::Clear,
+                           SpaceDecorator::DontMangle);
+  from_space()->initialize(fromMR,
+                           SpaceDecorator::DontClear,
+                           SpaceDecorator::DontMangle);
 
   assert(from_space()->top() == old_from_top, "from top changed!");
 
@@ -671,7 +800,7 @@
     st->print(" total " SIZE_FORMAT "K, used " SIZE_FORMAT "K",
                capacity_in_bytes()/K, used_in_bytes()/K);
   }
-  _virtual_space->print_space_boundaries_on(st);
+  virtual_space()->print_space_boundaries_on(st);
   st->print("  eden"); eden_space()->print_on(st);
   st->print("  from"); from_space()->print_on(st);
   st->print("  to  "); to_space()->print_on(st);
@@ -774,7 +903,9 @@
   // Was there a shrink of the survivor space?
   if (new_end < space_shrinking->end()) {
     MemRegion mr(space_shrinking->bottom(), new_end);
-    space_shrinking->initialize(mr, false /* clear */);
+    space_shrinking->initialize(mr,
+                                SpaceDecorator::DontClear,
+                                SpaceDecorator::Mangle);
   }
 }
 
@@ -809,3 +940,12 @@
   from_space()->verify(allow_dirty);
   to_space()->verify(allow_dirty);
 }
+
+#ifndef PRODUCT
+void PSYoungGen::record_spaces_top() {
+  assert(ZapUnusedHeapArea, "Not mangling unused space");
+  eden_space()->set_top_for_allocations();
+  from_space()->set_top_for_allocations();
+  to_space()->set_top_for_allocations();
+}
+#endif
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/parallelScavenge/psYoungGen.hpp
--- a/src/share/vm/gc_implementation/parallelScavenge/psYoungGen.hpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/gc_implementation/parallelScavenge/psYoungGen.hpp	Wed Jul 09 15:08:55 2008 -0700
@@ -179,4 +179,12 @@
 
   // Space boundary invariant checker
   void space_invariants() PRODUCT_RETURN;
+
+  // Helper for mangling survivor spaces.
+  void mangle_survivors(MutableSpace* s1,
+                        MemRegion s1MR,
+                        MutableSpace* s2,
+                        MemRegion s2MR) PRODUCT_RETURN;
+
+  void record_spaces_top() PRODUCT_RETURN;
 };
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/shared/mutableNUMASpace.cpp
--- a/src/share/vm/gc_implementation/shared/mutableNUMASpace.cpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/gc_implementation/shared/mutableNUMASpace.cpp	Wed Jul 09 15:08:55 2008 -0700
@@ -42,19 +42,31 @@
   delete lgrp_spaces();
 }
 
+#ifndef PRODUCT
 void MutableNUMASpace::mangle_unused_area() {
-  for (int i = 0; i < lgrp_spaces()->length(); i++) {
-    LGRPSpace *ls = lgrp_spaces()->at(i);
-    MutableSpace *s = ls->space();
-    if (!os::numa_has_static_binding()) {
-      HeapWord *top = MAX2((HeapWord*)round_down((intptr_t)s->top(), page_size()), s->bottom());
-      if (top < s->end()) {
-        ls->add_invalid_region(MemRegion(top, s->end()));
-      }
-    }
-    s->mangle_unused_area();
-  }
+  // This method should do nothing.
+  // It can be called on a numa space during a full compaction.
+}
+void MutableNUMASpace::mangle_unused_area_complete() {
+  // This method should do nothing.
+  // It can be called on a numa space during a full compaction.
+}
+void MutableNUMASpace::mangle_region(MemRegion mr) {
+  // This method should do nothing because numa spaces are not mangled.
 }
+void MutableNUMASpace::set_top_for_allocations(HeapWord* v) {
+  assert(false, "Do not mangle MutableNUMASpace's");
+}
+void MutableNUMASpace::set_top_for_allocations() {
+  // This method should do nothing.
+}
+void MutableNUMASpace::check_mangled_unused_area(HeapWord* limit) {
+  // This method should do nothing.
+}
+void MutableNUMASpace::check_mangled_unused_area_complete() {
+  // This method should do nothing.
+}
+#endif  // NOT_PRODUCT
 
 // There may be unallocated holes in the middle chunks
 // that should be filled with dead objects to ensure parseability.
@@ -243,7 +255,10 @@
       s->set_end(s->bottom());
       s->set_top(s->bottom());
     }
-    initialize(region(), true);
+    // A NUMA space is never mangled
+    initialize(region(),
+               SpaceDecorator::Clear,
+               SpaceDecorator::DontMangle);
   } else {
     bool should_initialize = false;
     if (!os::numa_has_static_binding()) {
@@ -257,7 +272,10 @@
 
     if (should_initialize ||
         (UseAdaptiveNUMAChunkSizing && adaptation_cycles() < samples_count())) {
-      initialize(region(), true);
+      // A NUMA space is never mangled
+      initialize(region(),
+                 SpaceDecorator::Clear,
+                 SpaceDecorator::DontMangle);
     }
   }
 
@@ -448,14 +466,17 @@
         }
 }
 
-void MutableNUMASpace::initialize(MemRegion mr, bool clear_space) {
+void MutableNUMASpace::initialize(MemRegion mr,
+                                  bool clear_space,
+                                  bool mangle_space) {
   assert(clear_space, "Reallocation will destory data!");
   assert(lgrp_spaces()->length() > 0, "There should be at least one space");
 
   MemRegion old_region = region(), new_region;
   set_bottom(mr.start());
   set_end(mr.end());
-  MutableSpace::set_top(bottom());
+  // Must always clear the space
+  clear(SpaceDecorator::DontMangle);
 
   // Compute chunk sizes
   size_t prev_page_size = page_size();
@@ -586,10 +607,8 @@
       bias_region(top_region, ls->lgrp_id());
     }
 
-    // If we clear the region, we would mangle it in debug. That would cause page
-    // allocation in a different place. Hence setting the top directly.
-    s->initialize(new_region, false);
-    s->set_top(s->bottom());
+    // Clear space (set top = bottom) but never mangle.
+    s->initialize(new_region, SpaceDecorator::Clear, SpaceDecorator::DontMangle);
 
     set_adaptation_cycles(samples_count());
   }
@@ -641,10 +660,12 @@
   MutableSpace::set_top(value);
 }
 
-void MutableNUMASpace::clear() {
+void MutableNUMASpace::clear(bool mangle_space) {
   MutableSpace::set_top(bottom());
   for (int i = 0; i < lgrp_spaces()->length(); i++) {
-    lgrp_spaces()->at(i)->space()->clear();
+    // Never mangle NUMA spaces because the mangling will
+    // bind the memory to a possibly unwanted lgroup.
+    lgrp_spaces()->at(i)->space()->clear(SpaceDecorator::DontMangle);
   }
 }
 
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/shared/mutableNUMASpace.hpp
--- a/src/share/vm/gc_implementation/shared/mutableNUMASpace.hpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/gc_implementation/shared/mutableNUMASpace.hpp	Wed Jul 09 15:08:55 2008 -0700
@@ -171,14 +171,21 @@
   MutableNUMASpace();
   virtual ~MutableNUMASpace();
   // Space initialization.
-  virtual void initialize(MemRegion mr, bool clear_space);
+  virtual void initialize(MemRegion mr, bool clear_space, bool mangle_space);
   // Update space layout if necessary. Do all adaptive resizing job.
   virtual void update();
   // Update allocation rate averages.
   virtual void accumulate_statistics();
 
-  virtual void clear();
-  virtual void mangle_unused_area();
+  virtual void clear(bool mangle_space);
+  virtual void mangle_unused_area() PRODUCT_RETURN;
+  virtual void mangle_unused_area_complete() PRODUCT_RETURN;
+  virtual void mangle_region(MemRegion mr) PRODUCT_RETURN;
+  virtual void check_mangled_unused_area(HeapWord* limit) PRODUCT_RETURN;
+  virtual void check_mangled_unused_area_complete() PRODUCT_RETURN;
+  virtual void set_top_for_allocations(HeapWord* v) PRODUCT_RETURN;
+  virtual void set_top_for_allocations() PRODUCT_RETURN;
+
   virtual void ensure_parsability();
   virtual size_t used_in_words() const;
   virtual size_t free_in_words() const;
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/shared/mutableSpace.cpp
--- a/src/share/vm/gc_implementation/shared/mutableSpace.cpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/gc_implementation/shared/mutableSpace.cpp	Wed Jul 09 15:08:55 2008 -0700
@@ -25,7 +25,17 @@
 # include "incls/_precompiled.incl"
 # include "incls/_mutableSpace.cpp.incl"
 
-void MutableSpace::initialize(MemRegion mr, bool clear_space) {
+MutableSpace::MutableSpace(): ImmutableSpace(), _top(NULL) {
+  _mangler = new MutableSpaceMangler(this);
+}
+
+MutableSpace::~MutableSpace() {
+  delete _mangler;
+}
+
+void MutableSpace::initialize(MemRegion mr,
+                              bool clear_space,
+                              bool mangle_space) {
   HeapWord* bottom = mr.start();
   HeapWord* end    = mr.end();
 
@@ -34,14 +44,51 @@
   set_bottom(bottom);
   set_end(end);
 
-  if (clear_space) clear();
+  if (clear_space) {
+    clear(mangle_space);
+  }
+}
+
+void MutableSpace::clear(bool mangle_space) {
+  set_top(bottom());
+  if (ZapUnusedHeapArea && mangle_space) {
+    mangle_unused_area();
+  }
+}
+
+#ifndef PRODUCT
+void MutableSpace::check_mangled_unused_area(HeapWord* limit) {
+  mangler()->check_mangled_unused_area(limit);
+}
+
+void MutableSpace::check_mangled_unused_area_complete() {
+  mangler()->check_mangled_unused_area_complete();
 }
 
-void MutableSpace::clear() {
-  set_top(bottom());
-  if (ZapUnusedHeapArea) mangle_unused_area();
+// Mangle only the unused space that has not previously
+// been mangled and that has not been allocated since being
+// mangled.
+void MutableSpace::mangle_unused_area() {
+  mangler()->mangle_unused_area();
+}
+
+void MutableSpace::mangle_unused_area_complete() {
+  mangler()->mangle_unused_area_complete();
 }
 
+void MutableSpace::mangle_region(MemRegion mr) {
+  SpaceMangler::mangle_region(mr);
+}
+
+void MutableSpace::set_top_for_allocations(HeapWord* v) {
+  mangler()->set_top_for_allocations(v);
+}
+
+void MutableSpace::set_top_for_allocations() {
+  mangler()->set_top_for_allocations(top());
+}
+#endif
+
 // This version requires locking. */
 HeapWord* MutableSpace::allocate(size_t size) {
   assert(Heap_lock->owned_by_self() ||
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/shared/mutableSpace.hpp
--- a/src/share/vm/gc_implementation/shared/mutableSpace.hpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/gc_implementation/shared/mutableSpace.hpp	Wed Jul 09 15:08:55 2008 -0700
@@ -30,14 +30,23 @@
 // Invariant: (ImmutableSpace +) bottom() <= top() <= end()
 // top() is inclusive and end() is exclusive.
 
+class MutableSpaceMangler;
+
 class MutableSpace: public ImmutableSpace {
   friend class VMStructs;
+
+  // Helper for mangling unused space in debug builds
+  MutableSpaceMangler* _mangler;
+
  protected:
   HeapWord* _top;
 
+  MutableSpaceMangler* mangler() { return _mangler; }
+
  public:
-  virtual ~MutableSpace()                  {}
-  MutableSpace()                           { _top = NULL;    }
+  virtual ~MutableSpace();
+  MutableSpace();
+
   // Accessors
   HeapWord* top() const                    { return _top;    }
   virtual void set_top(HeapWord* value)    { _top = value;   }
@@ -52,21 +61,30 @@
   MemRegion used_region() { return MemRegion(bottom(), top()); }
 
   // Initialization
-  virtual void initialize(MemRegion mr, bool clear_space);
-  virtual void clear();
+  virtual void initialize(MemRegion mr,
+                          bool clear_space,
+                          bool mangle_space);
+  virtual void clear(bool mangle_space);
+  // Does the usual initialization but optionally resets top to bottom.
+#if 0  // MANGLE_SPACE
+  void initialize(MemRegion mr, bool clear_space, bool reset_top);
+#endif
   virtual void update() { }
   virtual void accumulate_statistics() { }
 
-  // Overwrites the unused portion of this space. Note that some collectors
-  // may use this "scratch" space during collections.
-  virtual void mangle_unused_area() {
-    mangle_region(MemRegion(_top, _end));
-  }
+  // Methods used in mangling.  See descriptions under SpaceMangler.
+  virtual void mangle_unused_area() PRODUCT_RETURN;
+  virtual void mangle_unused_area_complete() PRODUCT_RETURN;
+  virtual void check_mangled_unused_area(HeapWord* limit) PRODUCT_RETURN;
+  virtual void check_mangled_unused_area_complete() PRODUCT_RETURN;
+  virtual void set_top_for_allocations(HeapWord* v) PRODUCT_RETURN;
+
+  // Used to save the space's current top for later use during mangling.
+  virtual void set_top_for_allocations() PRODUCT_RETURN;
+
   virtual void ensure_parsability() { }
 
-  void mangle_region(MemRegion mr) {
-    debug_only(Copy::fill_to_words(mr.start(), mr.word_size(), badHeapWord));
-  }
+  virtual void mangle_region(MemRegion mr) PRODUCT_RETURN;
 
   // Boolean querries.
   bool is_empty() const              { return used_in_words() == 0; }
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/shared/spaceDecorator.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/share/vm/gc_implementation/shared/spaceDecorator.cpp	Wed Jul 09 15:08:55 2008 -0700
@@ -0,0 +1,140 @@
+/*
+ * Copyright 2002-2005 Sun Microsystems, Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ *
+ */
+
+# include "incls/_precompiled.incl"
+# include "incls/_spaceDecorator.cpp.incl"
+
+// Catch-all file for utility classes
+
+#ifndef PRODUCT
+
+// Returns true is the location q matches the mangling
+// pattern.
+bool SpaceMangler::is_mangled(HeapWord* q) {
+  // This test loses precision but is good enough
+  return badHeapWord == (max_juint & (uintptr_t) q->value());
+}
+
+
+void SpaceMangler::set_top_for_allocations(HeapWord* v)  {
+  if (v < end()) {
+    assert(is_mangled(v), "The high water mark is not mangled");
+  }
+  _top_for_allocations = v;
+}
+
+// Mangle only the unused space that has not previously
+// been mangled and that has not been allocated since being
+// mangled.
+void SpaceMangler::mangle_unused_area() {
+  assert(ZapUnusedHeapArea, "Mangling should not be in use");
+  // Mangle between top and the high water mark.  Safeguard
+  // against the space changing since top_for_allocations was
+  // set.
+  HeapWord* mangled_end = MIN2(top_for_allocations(), end());
+  if (top() < mangled_end) {
+    MemRegion mangle_mr(top(), mangled_end);
+    SpaceMangler::mangle_region(mangle_mr);
+    // Light weight check of mangling.
+    check_mangled_unused_area(end());
+  }
+  // Complete check of unused area which is functional when
+  // DEBUG_MANGLING is defined.
+  check_mangled_unused_area_complete();
+}
+
+// A complete mangle is expected in the
+// exceptional case where top_for_allocations is not
+// properly tracking the high water mark for mangling.
+// This can be the case when to-space is being used for
+// scratch space during a mark-sweep-compact.  See
+// contribute_scratch() and PSMarkSweep::allocate_stacks().
+void SpaceMangler::mangle_unused_area_complete() {
+  assert(ZapUnusedHeapArea, "Mangling should not be in use");
+  MemRegion mangle_mr(top(), end());
+  SpaceMangler::mangle_region(mangle_mr);
+}
+
+// Simply mangle the MemRegion mr.
+void SpaceMangler::mangle_region(MemRegion mr) {
+  assert(ZapUnusedHeapArea, "Mangling should not be in use");
+#ifdef ASSERT
+  if(TraceZapUnusedHeapArea) {
+    gclog_or_tty->print("Mangling [0x%x to 0x%x)", mr.start(), mr.end());
+  }
+  Copy::fill_to_words(mr.start(), mr.word_size(), badHeapWord);
+  if(TraceZapUnusedHeapArea) {
+    gclog_or_tty->print_cr(" done");
+  }
+#endif
+}
+
+// Check that top, top_for_allocations and the last
+// word of the space are mangled.  In a tight memory
+// situation even this light weight mangling could
+// cause paging by touching the end of the space.
+void  SpaceMangler::check_mangled_unused_area(HeapWord* limit) {
+  if (CheckZapUnusedHeapArea) {
+    // This method can be called while the spaces are
+    // being reshaped so skip the test if the end of the
+    // space is beyond the specified limit;
+    if (end() > limit) return;
+
+    assert(top() == end() ||
+           (is_mangled(top())), "Top not mangled");
+    assert((top_for_allocations() < top()) ||
+           (top_for_allocations() >= end()) ||
+           (is_mangled(top_for_allocations())),
+           "Older unused not mangled");
+    assert(top() == end() ||
+           (is_mangled(end() - 1)), "End not properly mangled");
+    // Only does checking when DEBUG_MANGLING is defined.
+    check_mangled_unused_area_complete();
+  }
+}
+
+#undef DEBUG_MANGLING
+// This should only be used while debugging the mangling
+// because of the high cost of checking the completeness.
+void  SpaceMangler::check_mangled_unused_area_complete() {
+  if (CheckZapUnusedHeapArea) {
+    assert(ZapUnusedHeapArea, "Not mangling unused area");
+#ifdef DEBUG_MANGLING
+    HeapWord* q = top();
+    HeapWord* limit = end();
+
+    bool passed = true;
+    while (q < limit) {
+      if (!is_mangled(q)) {
+        passed = false;
+        break;
+      }
+      q++;
+    }
+    assert(passed, "Mangling is not complete");
+#endif
+  }
+}
+#undef DEBUG_MANGLING
+#endif // not PRODUCT
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/gc_implementation/shared/spaceDecorator.hpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/share/vm/gc_implementation/shared/spaceDecorator.hpp	Wed Jul 09 15:08:55 2008 -0700
@@ -0,0 +1,141 @@
+/*
+ * Copyright 2002-2005 Sun Microsystems, Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ *
+ */
+
+class SpaceDecorator: public AllStatic {
+ public:
+  // Initialization flags.
+  static const bool Clear               = true;
+  static const bool DontClear           = false;
+  static const bool Mangle              = true;
+  static const bool DontMangle          = false;
+};
+
+// Functionality for use with class Space and class MutableSpace.
+//   The approach taken with the mangling is to mangle all
+// the space initially and then to mangle areas that have
+// been allocated since the last collection.  Mangling is
+// done in the context of a generation and in the context
+// of a space.
+//   The space in a generation is mangled when it is first
+// initialized and when the generation grows.  The spaces
+// are not necessarily up-to-date when this mangling occurs
+// and the method mangle_region() is used.
+//   After allocations have been done in a space, the space generally
+// need to be remangled.  Remangling is only done on the
+// recently allocated regions in the space.  Typically, that is
+// the region between the new top and the top just before a
+// garbage collection.
+//   An exception to the usual mangling in a space is done when the
+// space is used for an extraordinary purpose.  Specifically, when
+// to-space is used as scratch space for a mark-sweep-compact
+// collection.
+//   Spaces are mangled after a collection.  If the generation
+// grows after a collection, the added space is mangled as part of
+// the growth of the generation.  No additional mangling is needed when the
+// spaces are resized after an expansion.
+//   The class SpaceMangler keeps a pointer to the top of the allocated
+// area and provides the methods for doing the piece meal mangling.
+// Methods for doing sparces and full checking of the mangling are
+// included.  The full checking is done if DEBUG_MANGLING is defined.
+//   GenSpaceMangler is used with the GenCollectedHeap collectors and
+// MutableSpaceMangler is used with the ParallelScavengeHeap collectors.
+// These subclasses abstract the differences in the types of spaces used
+// by each heap.
+
+class SpaceMangler: public CHeapObj {
+  friend class VMStructs;
+
+  // High water mark for allocations.  Typically, the space above
+  // this point have been mangle previously and don't need to be
+  // touched again.  Space belows this point has been allocated
+  // and remangling is needed between the current top and this
+  // high water mark.
+  HeapWord* _top_for_allocations;
+  HeapWord* top_for_allocations() { return _top_for_allocations; }
+
+ public:
+
+  // Setting _top_for_allocations to NULL at initialization
+  // makes it always below top so that mangling done as part
+  // of the initialize() call of a space does nothing (as it
+  // should since the mangling is done as part of the constructor
+  // for the space.
+  SpaceMangler() : _top_for_allocations(NULL) {}
+
+  // Methods for top and end that delegate to the specific
+  // space type.
+  virtual HeapWord* top() const = 0;
+  virtual HeapWord* end() const = 0;
+
+  // Return true if q matches the mangled pattern.
+  static bool is_mangled(HeapWord* q) PRODUCT_RETURN0;
+
+  // Used to save the an address in a space for later use during mangling.
+  void set_top_for_allocations(HeapWord* v);
+
+  // Overwrites the unused portion of this space.
+  // Mangle only the region not previously mangled [top, top_previously_mangled)
+  void mangle_unused_area();
+  // Mangle all the unused region [top, end)
+  void mangle_unused_area_complete();
+  // Do some sparse checking on the area that should have been mangled.
+  void check_mangled_unused_area(HeapWord* limit) PRODUCT_RETURN;
+  // Do a complete check of the area that should be mangled.
+  void check_mangled_unused_area_complete() PRODUCT_RETURN;
+
+  // Mangle the MemRegion.  This is a non-space specific mangler.  It
+  // is used during the initial mangling of a space before the space
+  // is fully constructed.  Also is used when a generation is expanded
+  // and possibly before the spaces have been reshaped to to the new
+  // size of the generation.
+  static void mangle_region(MemRegion mr);
+};
+
+class ContiguousSpace;
+
+// For use with GenCollectedHeap's
+class GenSpaceMangler: public SpaceMangler {
+  ContiguousSpace* _sp;
+
+  ContiguousSpace* sp() { return _sp; }
+
+  HeapWord* top() const { return _sp->top(); }
+  HeapWord* end() const { return _sp->end(); }
+
+ public:
+  GenSpaceMangler(ContiguousSpace* sp) : SpaceMangler(), _sp(sp) {}
+};
+
+// For use with ParallelScavengeHeap's.
+class MutableSpaceMangler: public SpaceMangler {
+  MutableSpace* _sp;
+
+  MutableSpace* sp() { return _sp; }
+
+  HeapWord* top() const { return _sp->top(); }
+  HeapWord* end() const { return _sp->end(); }
+
+ public:
+  MutableSpaceMangler(MutableSpace* sp) : SpaceMangler(), _sp(sp) {}
+};
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/includeDB_core
--- a/src/share/vm/includeDB_core	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/includeDB_core	Wed Jul 09 15:08:55 2008 -0700
@@ -1405,6 +1405,7 @@
 defNewGeneration.cpp                    oop.inline.hpp
 defNewGeneration.cpp                    referencePolicy.hpp
 defNewGeneration.cpp                    space.inline.hpp
+defNewGeneration.cpp                    spaceDecorator.hpp
 defNewGeneration.cpp                    thread_<os_family>.inline.hpp
 
 defNewGeneration.hpp                    ageTable.hpp
@@ -1789,6 +1790,7 @@
 generation.cpp                          java.hpp
 generation.cpp                          oop.hpp
 generation.cpp                          oop.inline.hpp
+generation.cpp                          spaceDecorator.hpp
 generation.cpp                          space.inline.hpp
 
 generation.hpp                          allocation.hpp
@@ -3722,6 +3724,7 @@
 space.cpp                               safepoint.hpp
 space.cpp                               space.hpp
 space.cpp                               space.inline.hpp
+space.cpp                               spaceDecorator.hpp
 space.cpp                               systemDictionary.hpp
 space.cpp                               universe.inline.hpp
 space.cpp                               vmSymbols.hpp
@@ -3744,6 +3747,13 @@
 space.inline.hpp                        space.hpp
 space.inline.hpp                        universe.hpp
 
+spaceDecorator.hpp                      globalDefinitions.hpp
+spaceDecorator.hpp                      mutableSpace.hpp
+spaceDecorator.hpp                      space.hpp
+
+spaceDecorator.cpp                      copy.hpp
+spaceDecorator.cpp                      spaceDecorator.hpp
+
 specialized_oop_closures.cpp            ostream.hpp
 specialized_oop_closures.cpp            specialized_oop_closures.hpp
 
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/includeDB_features
--- a/src/share/vm/includeDB_features	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/includeDB_features	Wed Jul 09 15:08:55 2008 -0700
@@ -51,6 +51,7 @@
 dump.cpp                                oopFactory.hpp
 dump.cpp                                resourceArea.hpp
 dump.cpp                                signature.hpp
+dump.cpp                                spaceDecorator.hpp
 dump.cpp                                symbolTable.hpp
 dump.cpp                                systemDictionary.hpp
 dump.cpp                                vmThread.hpp
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/memory/defNewGeneration.cpp
--- a/src/share/vm/memory/defNewGeneration.cpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/memory/defNewGeneration.cpp	Wed Jul 09 15:08:55 2008 -0700
@@ -172,15 +172,25 @@
   _to_counters = new CSpaceCounters("s1", 2, _max_survivor_size, _to_space,
                                     _gen_counters);
 
-  compute_space_boundaries(0);
+  compute_space_boundaries(0, SpaceDecorator::Clear, SpaceDecorator::Mangle);
   update_counters();
   _next_gen = NULL;
   _tenuring_threshold = MaxTenuringThreshold;
   _pretenure_size_threshold_words = PretenureSizeThreshold >> LogHeapWordSize;
 }
 
-void DefNewGeneration::compute_space_boundaries(uintx minimum_eden_size) {
-  uintx alignment = GenCollectedHeap::heap()->collector_policy()->min_alignment();
+void DefNewGeneration::compute_space_boundaries(uintx minimum_eden_size,
+                                                bool clear_space,
+                                                bool mangle_space) {
+  uintx alignment =
+    GenCollectedHeap::heap()->collector_policy()->min_alignment();
+
+  // If the spaces are being cleared (only done at heap initialization
+  // currently), the survivor spaces need not be empty.
+  // Otherwise, no care is taken for used areas in the survivor spaces
+  // so check.
+  assert(clear_space || (to()->is_empty() && from()->is_empty()),
+    "Initialization of the survivor spaces assumes these are empty");
 
   // Compute sizes
   uintx size = _virtual_space.committed_size();
@@ -214,16 +224,41 @@
   MemRegion fromMR((HeapWord*)from_start, (HeapWord*)to_start);
   MemRegion toMR  ((HeapWord*)to_start, (HeapWord*)to_end);
 
-  eden()->initialize(edenMR, (minimum_eden_size == 0));
-  // If minumum_eden_size != 0, we will not have cleared any
+  // A minimum eden size implies that there is a part of eden that
+  // is being used and that affects the initialization of any
+  // newly formed eden.
+  bool live_in_eden = minimum_eden_size > 0;
+
+  // If not clearing the spaces, do some checking to verify that
+  // the space are already mangled.
+  if (!clear_space) {
+    // Must check mangling before the spaces are reshaped.  Otherwise,
+    // the bottom or end of one space may have moved into another
+    // a failure of the check may not correctly indicate which space
+    // is not properly mangled.
+    if (ZapUnusedHeapArea) {
+      HeapWord* limit = (HeapWord*) _virtual_space.high();
+      eden()->check_mangled_unused_area(limit);
+      from()->check_mangled_unused_area(limit);
+        to()->check_mangled_unused_area(limit);
+    }
+  }
+
+  // Reset the spaces for their new regions.
+  eden()->initialize(edenMR,
+                     clear_space && !live_in_eden,
+                     SpaceDecorator::Mangle);
+  // If clear_space and live_in_eden, we will not have cleared any
   // portion of eden above its top. This can cause newly
   // expanded space not to be mangled if using ZapUnusedHeapArea.
   // We explicitly do such mangling here.
-  if (ZapUnusedHeapArea && (minimum_eden_size != 0)) {
+  if (ZapUnusedHeapArea && clear_space && live_in_eden && mangle_space) {
     eden()->mangle_unused_area();
   }
-  from()->initialize(fromMR, true);
-    to()->initialize(toMR  , true);
+  from()->initialize(fromMR, clear_space, mangle_space);
+  to()->initialize(toMR, clear_space, mangle_space);
+
+  // Set next compaction spaces.
   eden()->set_next_compaction_space(from());
   // The to-space is normally empty before a compaction so need
   // not be considered.  The exception is during promotion
@@ -250,7 +285,16 @@
 
 bool DefNewGeneration::expand(size_t bytes) {
   MutexLocker x(ExpandHeap_lock);
+  HeapWord* prev_high = (HeapWord*) _virtual_space.high();
   bool success = _virtual_space.expand_by(bytes);
+  if (success && ZapUnusedHeapArea) {
+    // Mangle newly committed space immediately because it
+    // can be done here more simply that after the new
+    // spaces have been computed.
+    HeapWord* new_high = (HeapWord*) _virtual_space.high();
+    MemRegion mangle_region(prev_high, new_high);
+    SpaceMangler::mangle_region(mangle_region);
+  }
 
   // Do not attempt an expand-to-the reserve size.  The
   // request should properly observe the maximum size of
@@ -262,7 +306,8 @@
   // value.
   if (GC_locker::is_active()) {
     if (PrintGC && Verbose) {
-      gclog_or_tty->print_cr("Garbage collection disabled, expanded heap instead");
+      gclog_or_tty->print_cr("Garbage collection disabled, "
+        "expanded heap instead");
     }
   }
 
@@ -326,16 +371,24 @@
     changed = true;
   }
   if (changed) {
-    compute_space_boundaries(eden()->used());
-    MemRegion cmr((HeapWord*)_virtual_space.low(), (HeapWord*)_virtual_space.high());
+    // The spaces have already been mangled at this point but
+    // may not have been cleared (set top = bottom) and should be.
+    // Mangling was done when the heap was being expanded.
+    compute_space_boundaries(eden()->used(),
+                             SpaceDecorator::Clear,
+                             SpaceDecorator::DontMangle);
+    MemRegion cmr((HeapWord*)_virtual_space.low(),
+                  (HeapWord*)_virtual_space.high());
     Universe::heap()->barrier_set()->resize_covered_region(cmr);
     if (Verbose && PrintGC) {
       size_t new_size_after  = _virtual_space.committed_size();
       size_t eden_size_after = eden()->capacity();
       size_t survivor_size_after = from()->capacity();
-      gclog_or_tty->print("New generation size " SIZE_FORMAT "K->" SIZE_FORMAT "K [eden="
+      gclog_or_tty->print("New generation size " SIZE_FORMAT "K->"
+        SIZE_FORMAT "K [eden="
         SIZE_FORMAT "K,survivor=" SIZE_FORMAT "K]",
-        new_size_before/K, new_size_after/K, eden_size_after/K, survivor_size_after/K);
+        new_size_before/K, new_size_after/K,
+        eden_size_after/K, survivor_size_after/K);
       if (WizardMode) {
         gclog_or_tty->print("[allowed " SIZE_FORMAT "K extra for %d threads]",
           thread_increase_size/K, threads_count);
@@ -480,7 +533,7 @@
   ScanWeakRefClosure scan_weak_ref(this);
 
   age_table()->clear();
-  to()->clear();
+  to()->clear(SpaceDecorator::Mangle);
 
   gch->rem_set()->prepare_for_younger_refs_iterate(false);
 
@@ -525,8 +578,18 @@
     soft_ref_policy, &is_alive, &keep_alive, &evacuate_followers, NULL);
   if (!promotion_failed()) {
     // Swap the survivor spaces.
-    eden()->clear();
-    from()->clear();
+    eden()->clear(SpaceDecorator::Mangle);
+    from()->clear(SpaceDecorator::Mangle);
+    if (ZapUnusedHeapArea) {
+      // This is now done here because of the piece-meal mangling which
+      // can check for valid mangling at intermediate points in the
+      // collection(s).  When a minor collection fails to collect
+      // sufficient space resizing of the young generation can occur
+      // an redistribute the spaces in the young generation.  Mangle
+      // here so that unzapped regions don't get distributed to
+      // other spaces.
+      to()->mangle_unused_area();
+    }
     swap_spaces();
 
     assert(to()->is_empty(), "to space should be empty now");
@@ -753,6 +816,15 @@
   }
 }
 
+void DefNewGeneration::reset_scratch() {
+  // If contributing scratch in to_space, mangle all of
+  // to_space if ZapUnusedHeapArea.  This is needed because
+  // top is not maintained while using to-space as scratch.
+  if (ZapUnusedHeapArea) {
+    to()->mangle_unused_area_complete();
+  }
+}
+
 bool DefNewGeneration::collection_attempt_is_safe() {
   if (!to()->is_empty()) {
     return false;
@@ -806,11 +878,25 @@
     }
   }
 
+  if (ZapUnusedHeapArea) {
+    eden()->check_mangled_unused_area_complete();
+    from()->check_mangled_unused_area_complete();
+    to()->check_mangled_unused_area_complete();
+  }
+
   // update the generation and space performance counters
   update_counters();
   gch->collector_policy()->counters()->update_counters();
 }
 
+void DefNewGeneration::record_spaces_top() {
+  assert(ZapUnusedHeapArea, "Not mangling unused space");
+  eden()->set_top_for_allocations();
+  to()->set_top_for_allocations();
+  from()->set_top_for_allocations();
+}
+
+
 void DefNewGeneration::update_counters() {
   if (UsePerfData) {
     _eden_counters->update_all();
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/memory/defNewGeneration.hpp
--- a/src/share/vm/memory/defNewGeneration.hpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/memory/defNewGeneration.hpp	Wed Jul 09 15:08:55 2008 -0700
@@ -279,6 +279,9 @@
   virtual void gc_prologue(bool full);
   virtual void gc_epilogue(bool full);
 
+  // Save the tops for eden, from, and to
+  virtual void record_spaces_top();
+
   // Doesn't require additional work during GC prologue and epilogue
   virtual bool performs_in_place_marking() const { return false; }
 
@@ -299,9 +302,12 @@
 
   // For non-youngest collection, the DefNewGeneration can contribute
   // "to-space".
-  void contribute_scratch(ScratchBlock*& list, Generation* requestor,
+  virtual void contribute_scratch(ScratchBlock*& list, Generation* requestor,
                           size_t max_alloc_words);
 
+  // Reset for contribution of "to-space".
+  virtual void reset_scratch();
+
   // GC support
   virtual void compute_new_size();
   virtual void collect(bool   full,
@@ -331,7 +337,12 @@
   void verify(bool allow_dirty);
 
  protected:
-  void compute_space_boundaries(uintx minimum_eden_size);
+  // If clear_space is true, clear the survivor spaces.  Eden is
+  // cleared if the minimum size of eden is 0.  If mangle_space
+  // is true, also mangle the space in debug mode.
+  void compute_space_boundaries(uintx minimum_eden_size,
+                                bool clear_space,
+                                bool mangle_space);
   // Scavenge support
   void swap_spaces();
 };
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/memory/dump.cpp
--- a/src/share/vm/memory/dump.cpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/memory/dump.cpp	Wed Jul 09 15:08:55 2008 -0700
@@ -645,7 +645,7 @@
 class ClearSpaceClosure : public SpaceClosure {
 public:
   void do_space(Space* s) {
-    s->clear();
+    s->clear(SpaceDecorator::Mangle);
   }
 };
 
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/memory/genCollectedHeap.cpp
--- a/src/share/vm/memory/genCollectedHeap.cpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/memory/genCollectedHeap.cpp	Wed Jul 09 15:08:55 2008 -0700
@@ -465,6 +465,11 @@
         _gens[i]->stat_record()->invocations++;
         _gens[i]->stat_record()->accumulated_time.start();
 
+        // Must be done anew before each collection because
+        // a previous collection will do mangling and will
+        // change top of some spaces.
+        record_gen_tops_before_GC();
+
         if (PrintGC && Verbose) {
           gclog_or_tty->print("level=%d invoke=%d size=" SIZE_FORMAT,
                      i,
@@ -1058,6 +1063,12 @@
   return res;
 }
 
+void GenCollectedHeap::release_scratch() {
+  for (int i = 0; i < _n_gens; i++) {
+    _gens[i]->reset_scratch();
+  }
+}
+
 size_t GenCollectedHeap::large_typearray_limit() {
   return gen_policy()->large_typearray_limit();
 }
@@ -1285,6 +1296,24 @@
   always_do_update_barrier = UseConcMarkSweepGC;
 };
 
+#ifndef PRODUCT
+class GenGCSaveTopsBeforeGCClosure: public GenCollectedHeap::GenClosure {
+ private:
+ public:
+  void do_generation(Generation* gen) {
+    gen->record_spaces_top();
+  }
+};
+
+void GenCollectedHeap::record_gen_tops_before_GC() {
+  if (ZapUnusedHeapArea) {
+    GenGCSaveTopsBeforeGCClosure blk;
+    generation_iterate(&blk, false);  // not old-to-young.
+    perm_gen()->record_spaces_top();
+  }
+}
+#endif  // not PRODUCT
+
 class GenEnsureParsabilityClosure: public GenCollectedHeap::GenClosure {
  public:
   void do_generation(Generation* gen) {
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/memory/genCollectedHeap.hpp
--- a/src/share/vm/memory/genCollectedHeap.hpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/memory/genCollectedHeap.hpp	Wed Jul 09 15:08:55 2008 -0700
@@ -259,6 +259,9 @@
   // be provided are returned as a list of ScratchBlocks, sorted by
   // decreasing size.
   ScratchBlock* gather_scratch(Generation* requestor, size_t max_alloc_words);
+  // Allow each generation to reset any scratch space that it has
+  // contributed as it needs.
+  void release_scratch();
 
   size_t large_typearray_limit();
 
@@ -482,6 +485,9 @@
   bool should_do_concurrent_full_gc(GCCause::Cause cause);
   void collect_mostly_concurrent(GCCause::Cause cause);
 
+  // Save the tops of the spaces in all generations
+  void record_gen_tops_before_GC() PRODUCT_RETURN;
+
 protected:
   virtual void gc_prologue(bool full);
   virtual void gc_epilogue(bool full);
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/memory/genMarkSweep.cpp
--- a/src/share/vm/memory/genMarkSweep.cpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/memory/genMarkSweep.cpp	Wed Jul 09 15:08:55 2008 -0700
@@ -190,6 +190,10 @@
 
 
 void GenMarkSweep::deallocate_stacks() {
+
+  GenCollectedHeap* gch = GenCollectedHeap::heap();
+  gch->release_scratch();
+
   if (_preserved_oop_stack) {
     delete _preserved_mark_stack;
     _preserved_mark_stack = NULL;
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/memory/generation.cpp
--- a/src/share/vm/memory/generation.cpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/memory/generation.cpp	Wed Jul 09 15:08:55 2008 -0700
@@ -32,6 +32,12 @@
     vm_exit_during_initialization("Could not reserve enough space for "
                     "object heap");
   }
+  // Mangle all of the the initial generation.
+  if (ZapUnusedHeapArea) {
+    MemRegion mangle_region((HeapWord*)_virtual_space.low(),
+      (HeapWord*)_virtual_space.high());
+    SpaceMangler::mangle_region(mangle_region);
+  }
   _reserved = MemRegion((HeapWord*)_virtual_space.low_boundary(),
           (HeapWord*)_virtual_space.high_boundary());
 }
@@ -505,8 +511,11 @@
     _bts->resize(new_word_size);
 
     // Fix for bug #4668531
-    MemRegion mangle_region(_the_space->end(), (HeapWord*)_virtual_space.high());
-    _the_space->mangle_region(mangle_region);
+    if (ZapUnusedHeapArea) {
+      MemRegion mangle_region(_the_space->end(),
+      (HeapWord*)_virtual_space.high());
+      SpaceMangler::mangle_region(mangle_region);
+    }
 
     // Expand space -- also expands space's BOT
     // (which uses (part of) shared array above)
@@ -622,6 +631,14 @@
 
   // update the generation and space performance counters
   update_counters();
+  if (ZapUnusedHeapArea) {
+    the_space()->check_mangled_unused_area_complete();
+  }
+}
+
+void OneContigSpaceCardGeneration::record_spaces_top() {
+  assert(ZapUnusedHeapArea, "Not mangling unused space");
+  the_space()->set_top_for_allocations();
 }
 
 void OneContigSpaceCardGeneration::verify(bool allow_dirty) {
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/memory/generation.hpp
--- a/src/share/vm/memory/generation.hpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/memory/generation.hpp	Wed Jul 09 15:08:55 2008 -0700
@@ -376,6 +376,9 @@
   // The default is to do nothing.
   virtual void gc_epilogue(bool full) {};
 
+  // Save the high water marks for the used space in a generation.
+  virtual void record_spaces_top() {};
+
   // Some generations may need to be "fixed-up" after some allocation
   // activity to make them parsable again. The default is to do nothing.
   virtual void ensure_parsability() {};
@@ -476,6 +479,10 @@
   virtual void contribute_scratch(ScratchBlock*& list, Generation* requestor,
                                   size_t max_alloc_words) {}
 
+  // Give each generation an opportunity to do clean up for any
+  // contributed scratch.
+  virtual void reset_scratch() {};
+
   // When an older generation has been collected, and perhaps resized,
   // this method will be invoked on all younger generations (from older to
   // younger), allowing them to resize themselves as appropriate.
@@ -699,6 +706,8 @@
 
   virtual void gc_epilogue(bool full);
 
+  virtual void record_spaces_top();
+
   virtual void verify(bool allow_dirty);
   virtual void print_on(outputStream* st) const;
 };
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/memory/space.cpp
--- a/src/share/vm/memory/space.cpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/memory/space.cpp	Wed Jul 09 15:08:55 2008 -0700
@@ -232,30 +232,44 @@
   return new ContiguousSpaceDCTOC(this, cl, precision, boundary);
 }
 
-void Space::initialize(MemRegion mr, bool clear_space) {
+void Space::initialize(MemRegion mr,
+                       bool clear_space,
+                       bool mangle_space) {
   HeapWord* bottom = mr.start();
   HeapWord* end    = mr.end();
   assert(Universe::on_page_boundary(bottom) && Universe::on_page_boundary(end),
          "invalid space boundaries");
   set_bottom(bottom);
   set_end(end);
-  if (clear_space) clear();
+  if (clear_space) clear(mangle_space);
+}
+
+void Space::clear(bool mangle_space) {
+  if (ZapUnusedHeapArea && mangle_space) {
+    mangle_unused_area();
+  }
 }
 
-void Space::clear() {
-  if (ZapUnusedHeapArea) mangle_unused_area();
+ContiguousSpace::ContiguousSpace(): CompactibleSpace(), _top(NULL) {
+  _mangler = new GenSpaceMangler(this);
 }
 
-void ContiguousSpace::initialize(MemRegion mr, bool clear_space)
+ContiguousSpace::~ContiguousSpace() {
+  delete _mangler;
+}
+
+void ContiguousSpace::initialize(MemRegion mr,
+                                 bool clear_space,
+                                 bool mangle_space)
 {
-  CompactibleSpace::initialize(mr, clear_space);
+  CompactibleSpace::initialize(mr, clear_space, mangle_space);
   _concurrent_iteration_safe_limit = top();
 }
 
-void ContiguousSpace::clear() {
+void ContiguousSpace::clear(bool mangle_space) {
   set_top(bottom());
   set_saved_mark();
-  Space::clear();
+  Space::clear(mangle_space);
 }
 
 bool Space::is_in(const void* p) const {
@@ -271,8 +285,8 @@
   return p >= _top;
 }
 
-void OffsetTableContigSpace::clear() {
-  ContiguousSpace::clear();
+void OffsetTableContigSpace::clear(bool mangle_space) {
+  ContiguousSpace::clear(mangle_space);
   _offsets.initialize_threshold();
 }
 
@@ -288,17 +302,46 @@
   Space::set_end(new_end);
 }
 
-void ContiguousSpace::mangle_unused_area() {
-  // to-space is used for storing marks during mark-sweep
-  mangle_region(MemRegion(top(), end()));
+#ifndef PRODUCT
+
+void ContiguousSpace::set_top_for_allocations(HeapWord* v) {
+  mangler()->set_top_for_allocations(v);
+}
+void ContiguousSpace::set_top_for_allocations() {
+  mangler()->set_top_for_allocations(top());
+}
+void ContiguousSpace::check_mangled_unused_area(HeapWord* limit) {
+  mangler()->check_mangled_unused_area(limit);
+}
+
+void ContiguousSpace::check_mangled_unused_area_complete() {
+  mangler()->check_mangled_unused_area_complete();
 }
 
-void ContiguousSpace::mangle_region(MemRegion mr) {
-  debug_only(Copy::fill_to_words(mr.start(), mr.word_size(), badHeapWord));
+// Mangled only the unused space that has not previously
+// been mangled and that has not been allocated since being
+// mangled.
+void ContiguousSpace::mangle_unused_area() {
+  mangler()->mangle_unused_area();
+}
+void ContiguousSpace::mangle_unused_area_complete() {
+  mangler()->mangle_unused_area_complete();
 }
+void ContiguousSpace::mangle_region(MemRegion mr) {
+  // Although this method uses SpaceMangler::mangle_region() which
+  // is not specific to a space, the when the ContiguousSpace version
+  // is called, it is always with regard to a space and this
+  // bounds checking is appropriate.
+  MemRegion space_mr(bottom(), end());
+  assert(space_mr.contains(mr), "Mangling outside space");
+  SpaceMangler::mangle_region(mr);
+}
+#endif  // NOT_PRODUCT
 
-void CompactibleSpace::initialize(MemRegion mr, bool clear_space) {
-  Space::initialize(mr, clear_space);
+void CompactibleSpace::initialize(MemRegion mr,
+                                  bool clear_space,
+                                  bool mangle_space) {
+  Space::initialize(mr, clear_space, mangle_space);
   _compaction_top = bottom();
   _next_compaction_space = NULL;
 }
@@ -820,8 +863,8 @@
   }
 }
 
-void EdenSpace::clear() {
-  ContiguousSpace::clear();
+void EdenSpace::clear(bool mangle_space) {
+  ContiguousSpace::clear(mangle_space);
   set_soft_end(end());
 }
 
@@ -878,7 +921,7 @@
   _par_alloc_lock(Mutex::leaf, "OffsetTableContigSpace par alloc lock", true)
 {
   _offsets.set_contig_space(this);
-  initialize(mr, true);
+  initialize(mr, SpaceDecorator::Clear, SpaceDecorator::Mangle);
 }
 
 
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/memory/space.hpp
--- a/src/share/vm/memory/space.hpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/memory/space.hpp	Wed Jul 09 15:08:55 2008 -0700
@@ -131,15 +131,17 @@
     return MemRegion(bottom(), saved_mark_word());
   }
 
-  // Initialization
-  virtual void initialize(MemRegion mr, bool clear_space);
-  virtual void clear();
+  // Initialization.  These may be run to reset an existing
+  // Space.
+  virtual void initialize(MemRegion mr, bool clear_space, bool mangle_space);
+  virtual void clear(bool mangle_space);
 
   // For detecting GC bugs.  Should only be called at GC boundaries, since
   // some unused space may be used as scratch space during GC's.
   // Default implementation does nothing. We also call this when expanding
   // a space to satisfy an allocation request. See bug #4668531
   virtual void mangle_unused_area() {}
+  virtual void mangle_unused_area_complete() {}
   virtual void mangle_region(MemRegion mr) {}
 
   // Testers
@@ -354,7 +356,7 @@
   CompactibleSpace* _next_compaction_space;
 
 public:
-  virtual void initialize(MemRegion mr, bool clear_space);
+  virtual void initialize(MemRegion mr, bool clear_space, bool mangle_space);
 
   // Used temporarily during a compaction phase to hold the value
   // top should have when compaction is complete.
@@ -724,12 +726,14 @@
   /* continuously, but those that weren't need to have their thresholds */      \
   /* re-initialized.  Also mangles unused area for debugging.           */      \
   if (is_empty()) {                                                             \
-    clear();                                                                    \
+    clear(SpaceDecorator::Mangle);                                              \
   } else {                                                                      \
     if (ZapUnusedHeapArea) mangle_unused_area();                                \
   }                                                                             \
 }
 
+class GenSpaceMangler;
+
 // A space in which the free area is contiguous.  It therefore supports
 // faster allocation, and compaction.
 class ContiguousSpace: public CompactibleSpace {
@@ -738,13 +742,21 @@
  protected:
   HeapWord* _top;
   HeapWord* _concurrent_iteration_safe_limit;
+  // A helper for mangling the unused area of the space in debug builds.
+  GenSpaceMangler* _mangler;
+
+  GenSpaceMangler* mangler() { return _mangler; }
 
   // Allocation helpers (return NULL if full).
   inline HeapWord* allocate_impl(size_t word_size, HeapWord* end_value);
   inline HeapWord* par_allocate_impl(size_t word_size, HeapWord* end_value);
 
  public:
-  virtual void initialize(MemRegion mr, bool clear_space);
+
+  ContiguousSpace();
+  ~ContiguousSpace();
+
+  virtual void initialize(MemRegion mr, bool clear_space, bool mangle_space);
 
   // Accessors
   HeapWord* top() const            { return _top;    }
@@ -753,15 +765,34 @@
   void set_saved_mark()       { _saved_mark_word = top();    }
   void reset_saved_mark()     { _saved_mark_word = bottom(); }
 
-  virtual void clear();
+  virtual void clear(bool mangle_space);
 
   WaterMark bottom_mark()     { return WaterMark(this, bottom()); }
   WaterMark top_mark()        { return WaterMark(this, top()); }
   WaterMark saved_mark()      { return WaterMark(this, saved_mark_word()); }
   bool saved_mark_at_top() const { return saved_mark_word() == top(); }
 
-  void mangle_unused_area();
-  void mangle_region(MemRegion mr);
+  // In debug mode mangle (write it with a particular bit
+  // pattern) the unused part of a space.
+
+  // Used to save the an address in a space for later use during mangling.
+  void set_top_for_allocations(HeapWord* v) PRODUCT_RETURN;
+  // Used to save the space's current top for later use during mangling.
+  void set_top_for_allocations() PRODUCT_RETURN;
+
+  // Mangle regions in the space from the current top up to the
+  // previously mangled part of the space.
+  void mangle_unused_area() PRODUCT_RETURN;
+  // Mangle [top, end)
+  void mangle_unused_area_complete() PRODUCT_RETURN;
+  // Mangle the given MemRegion.
+  void mangle_region(MemRegion mr) PRODUCT_RETURN;
+
+  // Do some sparse checking on the area that should have been mangled.
+  void check_mangled_unused_area(HeapWord* limit) PRODUCT_RETURN;
+  // Check the complete area that should have been mangled.
+  // This code may be NULL depending on the macro DEBUG_MANGLING.
+  void check_mangled_unused_area_complete() PRODUCT_RETURN;
 
   // Size computations: sizes in bytes.
   size_t capacity() const        { return byte_size(bottom(), end()); }
@@ -956,7 +987,7 @@
   void set_soft_end(HeapWord* value) { _soft_end = value; }
 
   // Override.
-  void clear();
+  void clear(bool mangle_space);
 
   // Set both the 'hard' and 'soft' limits (_end and _soft_end).
   void set_end(HeapWord* value) {
@@ -1000,7 +1031,7 @@
   void set_bottom(HeapWord* value);
   void set_end(HeapWord* value);
 
-  void clear();
+  void clear(bool mangle_space);
 
   inline HeapWord* block_start(const void* p) const;
 
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/runtime/globals.hpp
--- a/src/share/vm/runtime/globals.hpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/runtime/globals.hpp	Wed Jul 09 15:08:55 2008 -0700
@@ -589,9 +589,15 @@
   develop(bool, ZapJNIHandleArea, trueInDebug,                              \
           "Zap freed JNI handle space with 0xFEFEFEFE")                     \
                                                                             \
-  develop(bool, ZapUnusedHeapArea, false,                                   \
+  develop(bool, ZapUnusedHeapArea, trueInDebug,                             \
           "Zap unused heap space with 0xBAADBABE")                          \
                                                                             \
+  develop(bool, TraceZapUnusedHeapArea, false,                              \
+          "Trace zapping of unused heap space")                             \
+                                                                            \
+  develop(bool, CheckZapUnusedHeapArea, false,                              \
+          "Check zapping of unused heap space")                             \
+                                                                            \
   develop(bool, PrintVMMessages, true,                                      \
           "Print vm messages on console")                                   \
                                                                             \
diff -r 286bee59f34b -r 12eea04c8b06 src/share/vm/utilities/globalDefinitions.hpp
--- a/src/share/vm/utilities/globalDefinitions.hpp	Fri Jun 27 19:12:11 2008 -0700
+++ b/src/share/vm/utilities/globalDefinitions.hpp	Wed Jul 09 15:08:55 2008 -0700
@@ -97,8 +97,12 @@
 // object size.
 class HeapWord {
   friend class VMStructs;
-private:
+ private:
   char* i;
+#ifdef ASSERT
+ public:
+  char* value() { return i; }
+#endif
 };
 
 // HeapWordSize must be 2^LogHeapWordSize.