Wait for sweeper threads only if we have to.

src/mark-compact.cc

 // 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.
 
 #include "src/v8.h"
 
 #include "src/base/atomicops.h"
 #include "src/code-stubs.h"
 #include "src/compilation-cache.h"
 #include "src/cpu-profiler.h"
@@ skipping 629 matching lines @@
   space->AddToAccountingStats(freed_bytes);
   space->DecrementUnsweptFreeBytes(freed_bytes);
 }
 
 
 bool MarkCompactCollector::AreSweeperThreadsActivated() {
   return isolate()->sweeper_threads() != NULL || FLAG_job_based_sweeping;
 }
 
 
-bool MarkCompactCollector::IsConcurrentSweepingInProgress() {
-  return sweeping_pending_;
+bool MarkCompactCollector::IsConcurrentSweepingInProgress(PagedSpace* space) {
+  return (space == NULL || space->was_swept_concurrently()) &&
+      sweeping_pending_;
 }
 
 
 void Marking::TransferMark(Address old_start, Address new_start) {
   // This is only used when resizing an object.
   ASSERT(MemoryChunk::FromAddress(old_start) ==
          MemoryChunk::FromAddress(new_start));
 
   if (!heap_->incremental_marking()->IsMarking()) return;
 
@@ skipping 3412 matching lines @@
     }
     if (p == space->end_of_unswept_pages()) break;
   }
 }
 
 
 void MarkCompactCollector::SweepSpace(PagedSpace* space, SweeperType sweeper) {
   space->set_was_swept_conservatively(sweeper == CONSERVATIVE ||
                                       sweeper == PARALLEL_CONSERVATIVE ||
                                       sweeper == CONCURRENT_CONSERVATIVE);
+  space->set_was_swept_concurrently(sweeper == CONCURRENT_CONSERVATIVE);
   space->ClearStats();
 
   // We defensively initialize end_of_unswept_pages_ here with the first page
   // of the pages list.
   space->set_end_of_unswept_pages(space->FirstPage());
 
   PageIterator it(space);
 
   int pages_swept = 0;
   bool unused_page_present = false;
@@ skipping 395 matching lines @@
   while (buffer != NULL) {
     SlotsBuffer* next_buffer = buffer->next();
     DeallocateBuffer(buffer);
     buffer = next_buffer;
   }
   *buffer_address = NULL;
 }
 
 
 } }  // namespace v8::internal