Reland "[heap] Start sweeper tasks after evacuation" (second try).

src/heap/spaces.cc

 // Copyright 2011 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/heap/spaces.h"
 
 #include <utility>
 
 #include "src/base/bits.h"
 #include "src/base/platform/platform.h"
@@ skipping 377 matching lines @@
   std::list<MemoryChunk*> delayed_chunks(std::move(delayed_regular_chunks_));
   // Move constructed, so the permanent list should be empty.
   DCHECK(delayed_regular_chunks_.empty());
   for (auto it = delayed_chunks.begin(); it != delayed_chunks.end(); ++it) {
     AddMemoryChunkSafe<kRegular>(*it);
   }
 }
 
 bool MemoryAllocator::CanFreeMemoryChunk(MemoryChunk* chunk) {
   MarkCompactCollector* mc = isolate_->heap()->mark_compact_collector();
-  // We cannot free memory chunks in new space while the sweeper is running
-  // since a sweeper thread might be stuck right before trying to lock the
-  // corresponding page.
-  return !chunk->InNewSpace() || (mc == nullptr) || !FLAG_concurrent_sweeping ||
-         mc->sweeper().IsSweepingCompleted();
+  // We cannot free a memory chunk in new space while the sweeper is running
+  // because the memory chunk can be in the queue of a sweeper task.
+  // Chunks in old generation are unmapped if they are empty.
+  DCHECK(chunk->InNewSpace() || chunk->SweepingDone());
+  return !chunk->InNewSpace() || mc == nullptr || !FLAG_concurrent_sweeping ||
+         mc->sweeper().IsSweepingCompleted(NEW_SPACE);
 }
 
 bool MemoryAllocator::CommitMemory(Address base, size_t size,
                                    Executability executable) {
   if (!base::VirtualMemory::CommitRegion(base, size,
                                          executable == EXECUTABLE)) {
     return false;
   }
   UpdateAllocatedSpaceLimits(base, base + size);
   return true;
@@ skipping 2824 matching lines @@
     object->ShortPrint();
     PrintF("\n");
   }
   printf(" --------------------------------------\n");
   printf(" Marked: %x, LiveCount: %x\n", mark_size, LiveBytes());
 }
 
 #endif  // DEBUG
 }  // namespace internal
 }  // namespace v8