57   // Mangle between top and the high water mark.  Safeguard
  58   // against the space changing since top_for_allocations was
  59   // set.
  60   HeapWord* mangled_end = MIN2(top_for_allocations(), end());
  61   if (top() < mangled_end) {
  62     MemRegion mangle_mr(top(), mangled_end);
  63     SpaceMangler::mangle_region(mangle_mr);
  64     // Light weight check of mangling.
  65     check_mangled_unused_area(end());
  66   }
  67   // Complete check of unused area which is functional when
  68   // DEBUG_MANGLING is defined.
  69   check_mangled_unused_area_complete();
  70 }
  71 
  72 // A complete mangle is expected in the
  73 // exceptional case where top_for_allocations is not
  74 // properly tracking the high water mark for mangling.
  75 // This can be the case when to-space is being used for
  76 // scratch space during a mark-sweep-compact.  See
  77 // contribute_scratch() and PSMarkSweep::allocate_stacks().
  78 void SpaceMangler::mangle_unused_area_complete() {
  79   assert(ZapUnusedHeapArea, "Mangling should not be in use");
  80   MemRegion mangle_mr(top(), end());
  81   SpaceMangler::mangle_region(mangle_mr);
  82 }
  83 
  84 // Simply mangle the MemRegion mr.
  85 void SpaceMangler::mangle_region(MemRegion mr) {
  86   assert(ZapUnusedHeapArea, "Mangling should not be in use");
  87 #ifdef ASSERT
  88   Copy::fill_to_words(mr.start(), mr.word_size(), badHeapWord);
  89 #endif
  90 }
  91 
  92 // Check that top, top_for_allocations and the last
  93 // word of the space are mangled.  In a tight memory
  94 // situation even this light weight mangling could
  95 // cause paging by touching the end of the space.
  96 void  SpaceMangler::check_mangled_unused_area(HeapWord* limit) {
  97   if (CheckZapUnusedHeapArea) {

  57   // Mangle between top and the high water mark.  Safeguard
  58   // against the space changing since top_for_allocations was
  59   // set.
  60   HeapWord* mangled_end = MIN2(top_for_allocations(), end());
  61   if (top() < mangled_end) {
  62     MemRegion mangle_mr(top(), mangled_end);
  63     SpaceMangler::mangle_region(mangle_mr);
  64     // Light weight check of mangling.
  65     check_mangled_unused_area(end());
  66   }
  67   // Complete check of unused area which is functional when
  68   // DEBUG_MANGLING is defined.
  69   check_mangled_unused_area_complete();
  70 }
  71 
  72 // A complete mangle is expected in the
  73 // exceptional case where top_for_allocations is not
  74 // properly tracking the high water mark for mangling.
  75 // This can be the case when to-space is being used for
  76 // scratch space during a mark-sweep-compact.  See
  77 // contribute_scratch().
  78 void SpaceMangler::mangle_unused_area_complete() {
  79   assert(ZapUnusedHeapArea, "Mangling should not be in use");
  80   MemRegion mangle_mr(top(), end());
  81   SpaceMangler::mangle_region(mangle_mr);
  82 }
  83 
  84 // Simply mangle the MemRegion mr.
  85 void SpaceMangler::mangle_region(MemRegion mr) {
  86   assert(ZapUnusedHeapArea, "Mangling should not be in use");
  87 #ifdef ASSERT
  88   Copy::fill_to_words(mr.start(), mr.word_size(), badHeapWord);
  89 #endif
  90 }
  91 
  92 // Check that top, top_for_allocations and the last
  93 // word of the space are mangled.  In a tight memory
  94 // situation even this light weight mangling could
  95 // cause paging by touching the end of the space.
  96 void  SpaceMangler::check_mangled_unused_area(HeapWord* limit) {
  97   if (CheckZapUnusedHeapArea) {