[heap] MinorMC: Keep live bytes local in tasks

Keep the live bytes counter in a local hashmap. Merge back the counts
upon task destruction.

Bug: chromium:651354
Change-Id: Idd30e8fde690739d769a34e4650d8c0179fb5a75
Reviewed-on: https://chromium-review.googlesource.com/512642
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45488}

src/heap/mark-compact.cc

@@ -2330,7 +2330,12 @@ class YoungGenerationMarkingTask : public ItemParallelJob::Task {
       : ItemParallelJob::Task(isolate),
         collector_(collector),
         marking_deque_(marking_deque, task_id),
-        visitor_(isolate->heap(), marking_deque, task_id) {}
+        visitor_(isolate->heap(), marking_deque, task_id) {
+    local_live_bytes_.reserve(isolate->heap()->new_space()->Capacity() /
+                              Page::kPageSize);
+  }
+
+  ~YoungGenerationMarkingTask() { FlushLiveBytes(); }
 
   void RunInParallel() override {
     double marking_time = 0.0;
@@ -2357,7 +2362,7 @@ class YoungGenerationMarkingTask : public ItemParallelJob::Task {
     if (ObjectMarking::WhiteToGrey<MarkBit::ATOMIC>(
             heap_object, collector_->marking_state(heap_object))) {
       const int size = visitor_.Visit(heap_object);
-      marking_state(heap_object).IncrementLiveBytes<MarkBit::ATOMIC>(size);
+      IncrementLiveBytes(heap_object, size);
     }
   }
 
@@ -2370,7 +2375,7 @@ class YoungGenerationMarkingTask : public ItemParallelJob::Task {
     HeapObject* object = nullptr;
     while (marking_deque_.Pop(&object)) {
       const int size = visitor_.Visit(object);
-      marking_state(object).IncrementLiveBytes<MarkBit::ATOMIC>(size);
+      IncrementLiveBytes(object, size);
     }
   }
 
@@ -2379,14 +2384,27 @@ class YoungGenerationMarkingTask : public ItemParallelJob::Task {
     while (marking_deque_.WaitForMoreObjects()) {
       while (marking_deque_.Pop(&object)) {
         const int size = visitor_.Visit(object);
-        marking_state(object).IncrementLiveBytes<MarkBit::ATOMIC>(size);
+        IncrementLiveBytes(object, size);
       }
     }
   }
 
+  void IncrementLiveBytes(HeapObject* object, intptr_t bytes) {
+    local_live_bytes_[Page::FromAddress(reinterpret_cast<Address>(object))] +=
+        bytes;
+  }
+
+  void FlushLiveBytes() {
+    for (auto pair : local_live_bytes_) {
+      collector_->marking_state(pair.first)
+          .IncrementLiveBytes<MarkBit::ATOMIC>(pair.second);
+    }
+  }
+
   MinorMarkCompactCollector* collector_;
   LocalWorkStealingMarkingDeque marking_deque_;
   YoungGenerationMarkingVisitor visitor_;
+  std::unordered_map<Page*, intptr_t, Page::Hasher> local_live_bytes_;
 };
 
 class BatchedRootMarkingItem : public MarkingItem {

src/heap/spaces.h

@@ -236,6 +236,13 @@ class FreeListCategory {
 // any heap object.
 class MemoryChunk {
  public:
+  // Use with std data structures.
+  struct Hasher {
+    size_t operator()(Page* const p) const {
+      return reinterpret_cast<size_t>(p) >> kPageSizeBits;
+    }
+  };
+
   enum Flag {
     NO_FLAGS = 0u,
     IS_EXECUTABLE = 1u << 0,