--- old/src/share/vm/gc_implementation/shared/plab.hpp	2015-04-20 17:36:10.192773257 +0300
+++ new/src/share/vm/gc_implementation/shared/plab.hpp	2015-04-20 17:36:10.116772079 +0300
@@ -45,6 +45,7 @@
   // In support of ergonomic sizing of PLAB's
   size_t    _allocated;     // in HeapWord units
   size_t    _wasted;        // in HeapWord units
+  size_t    _undo_wasted;
   char      tail[32];
   static size_t AlignmentReserve;
 
@@ -62,6 +63,12 @@
   // the amount of remaining space.
   size_t retire_internal();
 
+  void add_undo_waste(HeapWord* obj, size_t word_sz);
+
+  // Undo the last allocation in the buffer, which is required to be of the
+  // "obj" of the given "word_sz".
+  void undo_last_allocation(HeapWord* obj, size_t word_sz);
+
 public:
   // Initializes the buffer to be empty, but with the given "word_sz".
   // Must get initialized with "set_buf" for an allocation to succeed.
@@ -90,18 +97,17 @@
   // Allocate the object aligned to "alignment_in_bytes".
   HeapWord* allocate_aligned(size_t word_sz, unsigned short alignment_in_bytes);
 
-  // Undo the last allocation in the buffer, which is required to be of the
+  // Undo any allocation in the buffer, which is required to be of the
   // "obj" of the given "word_sz".
-  void undo_allocation(HeapWord* obj, size_t word_sz) {
-    assert(pointer_delta(_top, _bottom) >= word_sz, "Bad undo");
-    assert(pointer_delta(_top, obj)     == word_sz, "Bad undo");
-    _top = obj;
-  }
+  void undo_allocation(HeapWord* obj, size_t word_sz);
 
   // The total (word) size of the buffer, including both allocated and
   // unallocated space.
   size_t word_sz() { return _word_sz; }
 
+  size_t waste() { return _wasted; }
+  size_t undo_waste() { return _undo_wasted; }
+
   // Should only be done if we are about to reset with a new buffer of the
   // given size.
   void set_word_size(size_t new_word_sz) {
@@ -146,20 +152,23 @@
 class PLABStats VALUE_OBJ_CLASS_SPEC {
   size_t _allocated;      // Total allocated
   size_t _wasted;         // of which wasted (internal fragmentation)
+  size_t _undo_wasted;    // of which wasted on undo (is not used for calculation of PLAB size)
   size_t _unused;         // Unused in last buffer
   size_t _desired_plab_sz;// Output of filter (below), suitably trimmed and quantized
   AdaptiveWeightedAverage
          _filter;         // Integrator with decay
 
   void reset() {
-    _allocated = 0;
-    _wasted    = 0;
-    _unused    = 0;
+    _allocated   = 0;
+    _wasted      = 0;
+    _undo_wasted = 0;
+    _unused      = 0;
   }
  public:
   PLABStats(size_t desired_plab_sz_, unsigned wt) :
     _allocated(0),
     _wasted(0),
+    _undo_wasted(0),
     _unused(0),
     _desired_plab_sz(desired_plab_sz_),
     _filter(wt)
@@ -192,6 +201,10 @@
   void add_wasted(size_t v) {
     Atomic::add_ptr(v, &_wasted);
   }
+
+  void add_undo_wasted(size_t v) {
+    Atomic::add_ptr(v, &_undo_wasted);
+  }
 };
 
 #endif // SHARE_VM_GC_IMPLEMENTATION_SHARED_PLAB_HPP