Estimate a (close) upper bound on the size of black-marked objects on each page.

src/incremental-marking.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 103 matching lines @@
   inline void RecordWriteOf(HeapObject* value);
   inline void RecordWrites(HeapObject* obj);
 
   inline void BlackToGreyAndUnshift(HeapObject* obj, MarkBit mark_bit);
 
   inline void WhiteToGreyAndPush(HeapObject* obj, MarkBit mark_bit);
 
   inline void WhiteToGrey(HeapObject* obj, MarkBit mark_bit);
 
   // Does white->black or grey->grey
-  inline void MarkBlackOrKeepGrey(MarkBit mark_bit) {
+  inline bool MarkBlackOrKeepGrey(MarkBit mark_bit) {
     ASSERT(!Marking::IsImpossible(mark_bit));
-    if (mark_bit.Get()) return;
+    if (mark_bit.Get()) return false;
     mark_bit.Set();
     ASSERT(!Marking::IsWhite(mark_bit));
     ASSERT(!Marking::IsImpossible(mark_bit));
+    return true;
   }
 
   inline int steps_count() {
     return steps_count_;
   }
 
   inline double steps_took() {
     return steps_took_;
   }
 
@@ skipping 49 matching lines @@
   int steps_count_;
   double steps_took_;
   bool should_hurry_;
   int allocation_marking_factor_;
   intptr_t allocated_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_INCREMENTAL_MARKING_H_