Introduce lazy sweeping.

src/mark-compact.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 279 matching lines @@
   static const uint32_t kMultiFreeEncoding = 1;
 
   inline bool IsMarked(Object* obj);
 
   inline Heap* heap() const { return heap_; }
 
   CodeFlusher* code_flusher() { return code_flusher_; }
   inline bool is_code_flushing_enabled() const { return code_flusher_ != NULL; }
   void EnableCodeFlushing(bool enable);
 
+  enum SweeperType {
+    CONSERVATIVE,
+    LAZY_CONSERVATIVE,
+    PRECISE
+  };
+
+  // Sweep a single page from the given space conservatively.
+  // Return a number of reclaimed bytes.
+  static int SweepConservatively(PagedSpace* space, Page* p);
+
  private:
   MarkCompactCollector();
   ~MarkCompactCollector();
 
 #ifdef DEBUG
   enum CollectorState {
     IDLE,
     PREPARE_GC,
     MARK_LIVE_OBJECTS,
     SWEEP_SPACES,
@@ skipping 142 matching lines @@
   int IterateLiveObjectsInRange(Address start, Address end,
                                 LiveObjectCallback size_func);
 
   // If we are not compacting the heap, we simply sweep the spaces except
   // for the large object space, clearing mark bits and adding unmarked
   // regions to each space's free list.
   void SweepSpaces();
 
   void SweepNewSpace(NewSpace* space);
 
-  enum SweeperType { CONSERVATIVE, PRECISE };
 
   void SweepSpace(PagedSpace* space, SweeperType sweeper);
 
+
 #ifdef DEBUG
   // -----------------------------------------------------------------------
   // Debugging variables, functions and classes
   // Counters used for debugging the marking phase of mark-compact or
   // mark-sweep collection.
 
   // Size of live objects in Heap::to_space_.
   int live_young_objects_size_;
 
   // Size of live objects in Heap::old_pointer_space_.
@@ skipping 29 matching lines @@
   CodeFlusher* code_flusher_;
 
   friend class Heap;
   friend class OverflowedObjectsScanner;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_MARK_COMPACT_H_