Forward white to grey transition only if slot is before the progress bar of a given object.

src/incremental-marking-inl.h

 // Copyright 2012 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 26 matching lines @@
 bool IncrementalMarking::BaseRecordWrite(HeapObject* obj,
                                          Object** slot,
                                          Object* value) {
   HeapObject* value_heap_obj = HeapObject::cast(value);
   MarkBit value_bit = Marking::MarkBitFrom(value_heap_obj);
   if (Marking::IsWhite(value_bit)) {
     MarkBit obj_bit = Marking::MarkBitFrom(obj);
     if (Marking::IsBlack(obj_bit)) {
       MemoryChunk* chunk = MemoryChunk::FromAddress(obj->address());
       if (chunk->IsFlagSet(MemoryChunk::HAS_PROGRESS_BAR)) {
-        WhiteToGreyAndPush(value_heap_obj, value_bit);
-        RestartIfNotMarking();
+        if (chunk->IsLeftOfProgressBar(slot)) {
+          WhiteToGreyAndPush(value_heap_obj, value_bit);
+          RestartIfNotMarking();
+        } else {
+          return false;
+        }
       } else {
         BlackToGreyAndUnshift(obj, obj_bit);
         RestartIfNotMarking();
         return false;
       }
     } else {
       return false;
     }
   }
   if (!is_compacting_) return false;
@@ skipping 73 matching lines @@
 
 void IncrementalMarking::WhiteToGreyAndPush(HeapObject* obj, MarkBit mark_bit) {
   Marking::WhiteToGrey(mark_bit);
   marking_deque_.PushGrey(obj);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_INCREMENTAL_MARKING_INL_H_