[heap] Remove delayed chunks in Unmapper

The dependency between restoring iterability and the Scavenger is
explicit. Delayed chunks are thus not needed anymore.

Bug: chromium:791043
Change-Id: I9f2c95c1856f53299af2737f922a3cb4cc578aa5
Reviewed-on: https://chromium-review.googlesource.com/805816Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49855}

src/heap/gc-tracer.cc

@@ -526,7 +526,6 @@ void GCTracer::PrintNVP() const {
           "semi_space_copy_rate=%.1f%% "
           "new_space_allocation_throughput=%.1f "
           "unmapper_chunks=%d "
-          "unmapper_delayed_chunks=%d "
           "context_disposal_rate=%.1f\n",
           duration, spent_in_mutator, current_.TypeName(true),
           current_.reduce_memory, current_.scopes[Scope::HEAP_PROLOGUE],
@@ -560,7 +559,6 @@ void GCTracer::PrintNVP() const {
           heap_->semi_space_copied_rate_,
           NewSpaceAllocationThroughputInBytesPerMillisecond(),
           heap_->memory_allocator()->unmapper()->NumberOfChunks(),
-          heap_->memory_allocator()->unmapper()->NumberOfDelayedChunks(),
           ContextDisposalRateInMilliseconds());
       break;
     case Event::MINOR_MARK_COMPACTOR:
@@ -707,7 +705,6 @@ void GCTracer::PrintNVP() const {
           "semi_space_copy_rate=%.1f%% "
           "new_space_allocation_throughput=%.1f "
           "unmapper_chunks=%d "
-          "unmapper_delayed_chunks=%d "
           "context_disposal_rate=%.1f "
           "compaction_speed=%.f\n",
           duration, spent_in_mutator, current_.TypeName(true),
@@ -791,7 +788,6 @@ void GCTracer::PrintNVP() const {
           heap_->semi_space_copied_rate_,
           NewSpaceAllocationThroughputInBytesPerMillisecond(),
           heap_->memory_allocator()->unmapper()->NumberOfChunks(),
-          heap_->memory_allocator()->unmapper()->NumberOfDelayedChunks(),
           ContextDisposalRateInMilliseconds(),
           CompactionSpeedInBytesPerMillisecond());
       break;

src/heap/heap.cc

@@ -1964,11 +1964,6 @@ void Heap::Scavenge() {
   IncrementalMarking::PauseBlackAllocationScope pause_black_allocation(
       incremental_marking());
 
-  if (mark_compact_collector()->sweeper()->sweeping_in_progress() &&
-      memory_allocator_->unmapper()->NumberOfDelayedChunks() >
-          static_cast<int>(new_space_->MaximumCapacity() / Page::kPageSize)) {
-    mark_compact_collector()->EnsureSweepingCompleted();
-  }
 
   mark_compact_collector()->sweeper()->EnsureIterabilityCompleted();
 

src/heap/mark-compact.cc

@@ -625,9 +625,6 @@ void MarkCompactCollector::EnsureSweepingCompleted() {
     verifier.Run();
   }
 #endif
-
-  if (heap()->memory_allocator()->unmapper()->has_delayed_chunks())
-    heap()->memory_allocator()->unmapper()->FreeQueuedChunks();
 }
 
 void MarkCompactCollector::ComputeEvacuationHeuristics(

src/heap/spaces.cc

@@ -326,7 +326,6 @@ class MemoryAllocator::Unmapper::UnmapFreeMemoryTask : public CancelableTask {
 };
 
 void MemoryAllocator::Unmapper::FreeQueuedChunks() {
-  ReconsiderDelayedChunks();
   if (heap_->use_tasks() && FLAG_concurrent_sweeping) {
     if (concurrent_unmapping_tasks_active_ >= kMaxUnmapperTasks) {
       // kMaxUnmapperTasks are already running. Avoid creating any more.
@@ -377,23 +376,12 @@ void MemoryAllocator::Unmapper::PerformFreeMemoryOnQueuedChunks() {
 
 void MemoryAllocator::Unmapper::TearDown() {
   CHECK_EQ(0, concurrent_unmapping_tasks_active_);
-  ReconsiderDelayedChunks();
-  CHECK(delayed_regular_chunks_.empty());
   PerformFreeMemoryOnQueuedChunks<FreeMode::kReleasePooled>();
   for (int i = 0; i < kNumberOfChunkQueues; i++) {
     DCHECK(chunks_[i].empty());
   }
 }
 
-void MemoryAllocator::Unmapper::ReconsiderDelayedChunks() {
-  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);
-  }
-}
-
 int MemoryAllocator::Unmapper::NumberOfChunks() {
   base::LockGuard<base::Mutex> guard(&mutex_);
   size_t result = 0;
@@ -403,16 +391,6 @@ int MemoryAllocator::Unmapper::NumberOfChunks() {
   return static_cast<int>(result);
 }
 
-bool MemoryAllocator::CanFreeMemoryChunk(MemoryChunk* chunk) {
-  MarkCompactCollector* mc = isolate_->heap()->mark_compact_collector();
-  // 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 ||
-         !mc->sweeper()->sweeping_in_progress();
-}
-
 bool MemoryAllocator::CommitMemory(Address base, size_t size,
                                    Executability executable) {
   if (!base::OS::SetPermissions(base, size,

src/heap/spaces.h

@@ -1225,14 +1225,6 @@ class V8_EXPORT_PRIVATE MemoryAllocator {
     void FreeQueuedChunks();
     void WaitUntilCompleted();
     void TearDown();
-
-    bool has_delayed_chunks() { return delayed_regular_chunks_.size() > 0; }
-
-    int NumberOfDelayedChunks() {
-      base::LockGuard<base::Mutex> guard(&mutex_);
-      return static_cast<int>(delayed_regular_chunks_.size());
-    }
-
     int NumberOfChunks();
 
    private:
@@ -1255,12 +1247,7 @@ class V8_EXPORT_PRIVATE MemoryAllocator {
     template <ChunkQueueType type>
     void AddMemoryChunkSafe(MemoryChunk* chunk) {
       base::LockGuard<base::Mutex> guard(&mutex_);
-      if (type != kRegular || allocator_->CanFreeMemoryChunk(chunk)) {
-        chunks_[type].push_back(chunk);
-      } else {
-        DCHECK_EQ(type, kRegular);
-        delayed_regular_chunks_.push_back(chunk);
-      }
+      chunks_[type].push_back(chunk);
     }
 
     template <ChunkQueueType type>
@@ -1272,7 +1259,6 @@ class V8_EXPORT_PRIVATE MemoryAllocator {
       return chunk;
     }
 
-    void ReconsiderDelayedChunks();
     template <FreeMode mode>
     void PerformFreeMemoryOnQueuedChunks();
 
@@ -1280,10 +1266,6 @@ class V8_EXPORT_PRIVATE MemoryAllocator {
     MemoryAllocator* const allocator_;
     base::Mutex mutex_;
     std::vector<MemoryChunk*> chunks_[kNumberOfChunkQueues];
-    // Delayed chunks cannot be processed in the current unmapping cycle because
-    // of dependencies such as an active sweeper.
-    // See MemoryAllocator::CanFreeMemoryChunk.
-    std::list<MemoryChunk*> delayed_regular_chunks_;
     CancelableTaskManager::Id task_ids_[kMaxUnmapperTasks];
     base::Semaphore pending_unmapping_tasks_semaphore_;
     intptr_t concurrent_unmapping_tasks_active_;
@@ -1344,8 +1326,6 @@ class V8_EXPORT_PRIVATE MemoryAllocator {
   template <MemoryAllocator::FreeMode mode = kFull>
   void Free(MemoryChunk* chunk);
 
-  bool CanFreeMemoryChunk(MemoryChunk* chunk);
-
   // Returns allocated spaces in bytes.
   size_t Size() { return size_.Value(); }