[heap] Emit trace event for background GC tasks.

The following events in v8.gc category are emitted:
- V8.GC_BACKGROUND_ARRAY_BUFFER_FREE
- V8.GC_BACKGROUND_STORE_BUFFER
- V8.GC_BACKGROUND_UNMAPPER
- V8.GC_MC_BACKGROUND_EVACUATE_COPY
- V8.GC_MC_BACKGROUND_EVACUATE_UPDATE_POINTERS
- V8.GC_MC_BACKGROUND_MARKING
- V8.GC_MC_BACKGROUND_SWEEPING
- V8.GC_MINOR_MC_BACKGROUND_EVACUATE_COPY
- V8.GC_MINOR_MC_BACKGROUND_EVACUATE_UPDATE_POINTERS
- V8.GC_MINOR_MC_BACKGROUND_MARKING
- V8.GC_SCAVENGER_BACKGROUND_SCAVENGE_PARALLEL

Bug: chromium:758183
Change-Id: I04368f75ac740cbc832a864609709e5a46f5baef
Reviewed-on: https://chromium-review.googlesource.com/825203
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50107}

src/heap/array-buffer-collector.cc

@@ -36,7 +36,7 @@ class ArrayBufferCollector::FreeingTask final : public CancelableTask {
 
  private:
   void RunInternal() final {
-    GCTracer::BackgroundScope scope(
+    TRACE_BACKGROUND_GC(
         heap_->tracer(),
         GCTracer::BackgroundScope::BACKGROUND_ARRAY_BUFFER_FREE);
     heap_->array_buffer_collector()->FreeAllocations();

src/heap/concurrent-marking.cc

@@ -439,8 +439,8 @@ ConcurrentMarking::ConcurrentMarking(Heap* heap, MarkingWorklist* shared,
 }
 
 void ConcurrentMarking::Run(int task_id, TaskState* task_state) {
-  GCTracer::BackgroundScope scope(
-      heap_->tracer(), GCTracer::BackgroundScope::MC_BACKGROUND_MARKING);
+  TRACE_BACKGROUND_GC(heap_->tracer(),
+                      GCTracer::BackgroundScope::MC_BACKGROUND_MARKING);
   size_t kBytesUntilInterruptCheck = 64 * KB;
   int kObjectsUntilInterrupCheck = 1000;
   LiveBytesMap* live_bytes = nullptr;

src/heap/gc-tracer.cc

@@ -80,7 +80,22 @@ const char* GCTracer::Scope::Name(ScopeId id) {
       break;
   }
 #undef CASE
-  return "(unknown)";
+  UNREACHABLE();
+  return nullptr;
+}
+
+const char* GCTracer::BackgroundScope::Name(ScopeId id) {
+#define CASE(scope)            \
+  case BackgroundScope::scope: \
+    return "V8.GC_" #scope;
+  switch (id) {
+    TRACER_BACKGROUND_SCOPES(CASE)
+    case BackgroundScope::NUMBER_OF_SCOPES:
+      break;
+  }
+#undef CASE
+  UNREACHABLE();
+  return nullptr;
 }
 
 GCTracer::Event::Event(Type type, GarbageCollectionReason gc_reason,

src/heap/gc-tracer.h

@@ -31,6 +31,11 @@ enum ScavengeSpeedMode { kForAllObjects, kForSurvivedObjects };
   TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("v8.gc"),             \
                GCTracer::Scope::Name(gc_tracer_scope_id))
 
+#define TRACE_BACKGROUND_GC(tracer, scope_id)                   \
+  GCTracer::BackgroundScope background_scope(tracer, scope_id); \
+  TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("v8.gc"),              \
+               GCTracer::BackgroundScope::Name(scope_id))
+
 // GCTracer collects and prints ONE line after each garbage collector
 // invocation IFF --trace_gc is used.
 class V8_EXPORT_PRIVATE GCTracer {
@@ -109,6 +114,8 @@ class V8_EXPORT_PRIVATE GCTracer {
     BackgroundScope(GCTracer* tracer, ScopeId scope);
     ~BackgroundScope();
 
+    static const char* Name(ScopeId id);
+
    private:
     GCTracer* tracer_;
     ScopeId scope_;

src/heap/heap.cc

@@ -1920,7 +1920,7 @@ class ScavengingTask final : public ItemParallelJob::Task {
         barrier_(barrier) {}
 
   void RunInParallel() final {
-    GCTracer::BackgroundScope scope(
+    TRACE_BACKGROUND_GC(
         heap_->tracer(),
         GCTracer::BackgroundScope::SCAVENGER_BACKGROUND_SCAVENGE_PARALLEL);
     double scavenging_time = 0.0;

src/heap/mark-compact.cc

@@ -1853,9 +1853,8 @@ class YoungGenerationMarkingTask : public ItemParallelJob::Task {
   }
 
   void RunInParallel() override {
-    GCTracer::BackgroundScope scope(
-        collector_->heap()->tracer(),
-        GCTracer::BackgroundScope::MINOR_MC_BACKGROUND_MARKING);
+    TRACE_BACKGROUND_GC(collector_->heap()->tracer(),
+                        GCTracer::BackgroundScope::MINOR_MC_BACKGROUND_MARKING);
     double marking_time = 0.0;
     {
       TimedScope scope(&marking_time);
@@ -3244,8 +3243,7 @@ class PageEvacuationTask : public ItemParallelJob::Task {
         tracer_(isolate->heap()->tracer()) {}
 
   void RunInParallel() override {
-    GCTracer::BackgroundScope scope(tracer_,
-                                    evacuator_->GetBackgroundTracingScope());
+    TRACE_BACKGROUND_GC(tracer_, evacuator_->GetBackgroundTracingScope());
     PageEvacuationItem* item = nullptr;
     while ((item = GetItem<PageEvacuationItem>()) != nullptr) {
       evacuator_->EvacuatePage(item->page());
@@ -3561,7 +3559,7 @@ class PointersUpdatingTask : public ItemParallelJob::Task {
         scope_(scope) {}
 
   void RunInParallel() override {
-    GCTracer::BackgroundScope scope(tracer_, scope_);
+    TRACE_BACKGROUND_GC(tracer_, scope_);
     UpdatingItem* item = nullptr;
     while ((item = GetItem<UpdatingItem>()) != nullptr) {
       item->Process();

src/heap/spaces.cc

@@ -320,8 +320,8 @@ class MemoryAllocator::Unmapper::UnmapFreeMemoryTask : public CancelableTask {
 
  private:
   void RunInternal() override {
-    GCTracer::BackgroundScope scope(
-        tracer_, GCTracer::BackgroundScope::BACKGROUND_UNMAPPER);
+    TRACE_BACKGROUND_GC(tracer_,
+                        GCTracer::BackgroundScope::BACKGROUND_UNMAPPER);
     unmapper_->PerformFreeMemoryOnQueuedChunks<FreeMode::kUncommitPooled>();
     unmapper_->pending_unmapping_tasks_semaphore_.Signal();
   }

src/heap/store-buffer.h

@@ -175,8 +175,8 @@ class StoreBuffer {
 
    private:
     void RunInternal() override {
-      GCTracer::BackgroundScope scope(
-          tracer_, GCTracer::BackgroundScope::BACKGROUND_STORE_BUFFER);
+      TRACE_BACKGROUND_GC(tracer_,
+                          GCTracer::BackgroundScope::BACKGROUND_STORE_BUFFER);
       store_buffer_->ConcurrentlyProcessStoreBuffer();
     }
     StoreBuffer* store_buffer_;

src/heap/sweeper.cc

@@ -76,8 +76,8 @@ class Sweeper::SweeperTask final : public CancelableTask {
 
  private:
   void RunInternal() final {
-    GCTracer::BackgroundScope scope(
-        tracer_, GCTracer::BackgroundScope::MC_BACKGROUND_SWEEPING);
+    TRACE_BACKGROUND_GC(tracer_,
+                        GCTracer::BackgroundScope::MC_BACKGROUND_SWEEPING);
     DCHECK_GE(space_to_start_, FIRST_PAGED_SPACE);
     DCHECK_LE(space_to_start_, LAST_PAGED_SPACE);
     const int offset = space_to_start_ - FIRST_PAGED_SPACE;
@@ -529,8 +529,8 @@ class Sweeper::IterabilityTask final : public CancelableTask {
 
  private:
   void RunInternal() final {
-    GCTracer::BackgroundScope scope(
-        tracer_, GCTracer::BackgroundScope::MC_BACKGROUND_SWEEPING);
+    TRACE_BACKGROUND_GC(tracer_,
+                        GCTracer::BackgroundScope::MC_BACKGROUND_SWEEPING);
     for (Page* page : sweeper_->iterability_list_) {
       sweeper_->MakeIterable(page);
     }