Tweak compaction candidate selection to avoid keeping page with low occupancy around.

src/mark-compact.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 356 matching lines @@
 
   static bool AddTo(SlotsBufferAllocator* allocator,
                     SlotsBuffer** buffer_address,
                     SlotType type,
                     Address addr,
                     AdditionMode mode);
 
   static const int kNumberOfElements = 1021;
 
  private:
-  static const int kChainLengthThreshold = 6;
+  static const int kChainLengthThreshold = 15;
 
   intptr_t idx_;
   intptr_t chain_length_;
   SlotsBuffer* next_;
   ObjectSlot slots_[kNumberOfElements];
 };
 
 
 // Defined in isolate.h.
 class ThreadLocalTop;
@@ skipping 177 matching lines @@
   };
 
   // The current stage of the collector.
   CollectorState state_;
 #endif
 
   // Global flag that forces sweeping to be precise, so we can traverse the
   // heap.
   bool sweep_precisely_;
 
+  bool reduce_memory_footprint_;
+
   // True if we are collecting slots to perform evacuation from evacuation
   // candidates.
   bool compacting_;
 
   bool was_marked_incrementally_;
 
   bool collect_maps_;
 
   bool flush_monomorphic_ics_;
 
@@ skipping 174 matching lines @@
 
   friend class Heap;
 };
 
 
 const char* AllocationSpaceName(AllocationSpace space);
 
 } }  // namespace v8::internal
 
 #endif  // V8_MARK_COMPACT_H_