Make heap size estimation more accurate.

src/spaces.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1451 matching lines @@
   // The bytes in the linear allocation area are not included in this total
   // because updating the stats would slow down allocation.  New pages are
   // immediately added to the free list so they show up here.
   intptr_t Available() { return free_list_.available(); }
 
   // Allocated bytes in this space.  Garbage bytes that were not found due to
   // lazy sweeping are counted as being allocated!  The bytes in the current
   // linear allocation area (between top and limit) are also counted here.
   virtual intptr_t Size() { return accounting_stats_.Size(); }
 
-  // As size, but the bytes in the current linear allocation area are not
-  // included.
-  virtual intptr_t SizeOfObjects() { return Size() - (limit() - top()); }
+  // As size, but the bytes in lazily swept pages are estimated and the bytes
+  // in the current linear allocation area are not included.
+  intptr_t SizeOfObjectsSlow();
+  virtual intptr_t SizeOfObjects() {
+    if (IsSweepingComplete()) {
+      return Size() - (limit() - top());
+    } else {
+      return SizeOfObjectsSlow();
+    }
+  }
 
   // Wasted bytes in this space.  These are just the bytes that were thrown away
   // due to being too small to use for allocation.  They do not include the
   // free bytes that were not found at all due to lazy sweeping.
   virtual intptr_t Waste() { return accounting_stats_.Waste(); }
 
   // Returns the allocation pointer in this space.
-  Address top() {
-    return allocation_info_.top;
-  }
+  Address top() { return allocation_info_.top; }
   Address limit() { return allocation_info_.limit; }
 
   // Allocate the requested number of bytes in the space if possible, return a
   // failure object if not.
   MUST_USE_RESULT inline MaybeObject* AllocateRaw(int size_in_bytes);
 
   virtual bool ReserveSpace(int bytes);
 
   // Give a block of memory to the space's free list.  It might be added to
   // the free list or accounted as waste.
@@ skipping 1135 matching lines @@
   }
   // Must be small, since an iteration is used for lookup.
   static const int kMaxComments = 64;
 };
 #endif
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_SPACES_H_