Allow main thread to contribute to the sweeping phase.

src/mark-compact.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_MARK_COMPACT_H_
 #define V8_MARK_COMPACT_H_
 
 #include "src/compiler-intrinsics.h"
 #include "src/spaces.h"
 
@@ skipping 559 matching lines @@
   void EnableCodeFlushing(bool enable);
 
   enum SweeperType {
     CONSERVATIVE,
     PARALLEL_CONSERVATIVE,
     CONCURRENT_CONSERVATIVE,
     PRECISE
   };
 
   enum SweepingParallelism {
-    SWEEP_SEQUENTIALLY,
+    SWEEP_ON_MAIN_THREAD,
     SWEEP_IN_PARALLEL
   };
 
 #ifdef VERIFY_HEAP
   void VerifyMarkbitsAreClean();
   static void VerifyMarkbitsAreClean(PagedSpace* space);
   static void VerifyMarkbitsAreClean(NewSpace* space);
   void VerifyWeakEmbeddedObjectsInCode();
   void VerifyOmittedMapChecks();
 #endif
 
   // Sweep a single page from the given space conservatively.
-  // Return a number of reclaimed bytes.
+  // Returns the size of the biggest continuous freed memory chunk in bytes.
   template<SweepingParallelism type>
   static intptr_t SweepConservatively(PagedSpace* space,
                                       FreeList* free_list,
                                       Page* p);
 
   INLINE(static bool ShouldSkipEvacuationSlotRecording(Object** anchor)) {
     return Page::FromAddress(reinterpret_cast<Address>(anchor))->
         ShouldSkipEvacuationSlotRecording();
   }
 
@@ skipping 48 matching lines @@
   void InvalidateCode(Code* code);
 
   void ClearMarkbits();
 
   bool abort_incremental_marking() const { return abort_incremental_marking_; }
 
   bool is_compacting() const { return compacting_; }
 
   MarkingParity marking_parity() { return marking_parity_; }
 
-  // Concurrent and parallel sweeping support.
-  void SweepInParallel(PagedSpace* space);
+  // Concurrent and parallel sweeping support. If required_freed_bytes was set
+  // to a value larger than 0, then sweeping returns after a block of at least
+  // required_freed_bytes was freed. If required_freed_bytes was set to zero
+  // then the whole given space is swept.
+  template<SweepingParallelism type>
+  int SweepInParallel(PagedSpace* space, int required_freed_bytes);
 
   void WaitUntilSweepingCompleted();
 
   bool IsSweepingCompleted();
 
   void RefillFreeList(PagedSpace* space);
 
   bool AreSweeperThreadsActivated();
 
   // If a paged space is passed in, this method checks if the given space is
@@ skipping 308 matching lines @@
  private:
   MarkCompactCollector* collector_;
 };
 
 
 const char* AllocationSpaceName(AllocationSpace space);
 
 } }  // namespace v8::internal
 
 #endif  // V8_MARK_COMPACT_H_