Reland "[heap] Add epoch to GC tracing events"

This is a reland of be52501d

Fix data race by not emitting the epoch for sweeper background jobs
at them moment.

Original change's description:
> [heap] Add epoch to GC tracing events
>
> This CL adds the TRACE_GC_EPOCH macro, which adds the epoch as attribute
> to the trace event. Use TRACE_GC_EPOCH for top-level events, nested
> events can get the information from its parent.
>
> V8's GC needs an epoch for young and full collections, since scavenges
> also occur during incremental marking. The epoch is also process-wide,
> so different isolates do not reuse the same id.
>
> Change-Id: I8889bccce51e008374b4796445a50062bd87a45d
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2565247
> Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#71521}

Change-Id: Ib8f4bfdc01c459955eb6db63bb6e24a8aa068f09
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2567702
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71567}

src/heap/concurrent-marking.cc

@@ -400,8 +400,8 @@ ConcurrentMarking::ConcurrentMarking(Heap* heap,
 
 void ConcurrentMarking::Run(JobDelegate* delegate, unsigned mark_compact_epoch,
                             bool is_forced_gc) {
-  TRACE_GC1(heap_->tracer(), GCTracer::Scope::MC_BACKGROUND_MARKING,
-            ThreadKind::kBackground);
+  TRACE_GC_EPOCH(heap_->tracer(), GCTracer::Scope::MC_BACKGROUND_MARKING,
+                 ThreadKind::kBackground);
   size_t kBytesUntilInterruptCheck = 64 * KB;
   int kObjectsUntilInterrupCheck = 1000;
   uint8_t task_id = delegate->GetTaskId() + 1;

src/heap/gc-tracer.cc

@@ -48,6 +48,14 @@ double GCTracer::MonotonicallyIncreasingTimeInMs() {
   }
 }
 
+CollectionEpoch GCTracer::CurrentEpoch(Scope::ScopeId scope_id) {
+  if (Scope::NeedsYoungEpoch(scope_id)) {
+    return heap_->epoch_young();
+  } else {
+    return heap_->epoch_full();
+  }
+}
+
 GCTracer::Scope::Scope(GCTracer* tracer, ScopeId scope, ThreadKind thread_kind)
     : tracer_(tracer), scope_(scope), thread_kind_(thread_kind) {
   start_time_ = tracer_->MonotonicallyIncreasingTimeInMs();
@@ -95,6 +103,19 @@ const char* GCTracer::Scope::Name(ScopeId id) {
   return nullptr;
 }
 
+bool GCTracer::Scope::NeedsYoungEpoch(ScopeId id) {
+#define CASE(scope)  \
+  case Scope::scope: \
+    return true;
+  switch (id) {
+    TRACER_YOUNG_EPOCH_SCOPES(CASE)
+    default:
+      return false;
+  }
+#undef CASE
+  UNREACHABLE();
+}
+
 GCTracer::Event::Event(Type type, GarbageCollectionReason gc_reason,
                        const char* collector_reason)
     : type(type),

src/heap/gc-tracer.h

@@ -41,6 +41,13 @@ enum ScavengeSpeedMode { kForAllObjects, kForSurvivedObjects };
   GCTracer::Scope gc_tracer_scope(tracer, gc_tracer_scope_id, thread_kind); \
   TRACE_EVENT0(TRACE_GC_CATEGORIES, GCTracer::Scope::Name(gc_tracer_scope_id))
 
+#define TRACE_GC_EPOCH(tracer, scope_id, thread_kind)                          \
+  GCTracer::Scope::ScopeId gc_tracer_scope_id(scope_id);                       \
+  GCTracer::Scope gc_tracer_scope(tracer, gc_tracer_scope_id, thread_kind);    \
+  CollectionEpoch epoch = tracer->CurrentEpoch(scope_id);                      \
+  TRACE_EVENT1(TRACE_GC_CATEGORIES, GCTracer::Scope::Name(gc_tracer_scope_id), \
+               "epoch", epoch)
+
 // GCTracer collects and prints ONE line after each garbage collector
 // invocation IFF --trace_gc is used.
 class V8_EXPORT_PRIVATE GCTracer {
@@ -99,6 +106,7 @@ class V8_EXPORT_PRIVATE GCTracer {
     Scope(const Scope&) = delete;
     Scope& operator=(const Scope&) = delete;
     static const char* Name(ScopeId id);
+    static bool NeedsYoungEpoch(ScopeId id);
 
    private:
     GCTracer* tracer_;
@@ -337,6 +345,8 @@ class V8_EXPORT_PRIVATE GCTracer {
 
   WorkerThreadRuntimeCallStats* worker_thread_runtime_call_stats();
 
+  CollectionEpoch CurrentEpoch(Scope::ScopeId id);
+
  private:
   FRIEND_TEST(GCTracer, AverageSpeed);
   FRIEND_TEST(GCTracerTest, AllocationThroughput);

src/heap/heap.cc

@@ -104,6 +104,14 @@
 namespace v8 {
 namespace internal {
 
+namespace {
+std::atomic<CollectionEpoch> global_epoch{0};
+
+CollectionEpoch next_epoch() {
+  return global_epoch.fetch_add(1, std::memory_order_relaxed) + 1;
+}
+}  // namespace
+
 #ifdef V8_ENABLE_THIRD_PARTY_HEAP
 Isolate* Heap::GetIsolateFromWritableObject(HeapObject object) {
   return reinterpret_cast<Isolate*>(
@@ -1733,6 +1741,10 @@ void Heap::StartIncrementalMarking(int gc_flags,
                                    GarbageCollectionReason gc_reason,
                                    GCCallbackFlags gc_callback_flags) {
   DCHECK(incremental_marking()->IsStopped());
+
+  // The next GC cycle begins here.
+  UpdateEpochFull();
+
   SafepointScope safepoint(this);
   set_current_gc_flags(gc_flags);
   current_gc_callback_flags_ = gc_callback_flags;
@@ -1946,23 +1958,43 @@ void Heap::UpdateSurvivalStatistics(int start_new_space_size) {
   tracer()->AddSurvivalRatio(survival_rate);
 }
 
+namespace {
+GCTracer::Scope::ScopeId CollectorScopeId(GarbageCollector collector) {
+  switch (collector) {
+    case MARK_COMPACTOR:
+      return GCTracer::Scope::ScopeId::MARK_COMPACTOR;
+    case MINOR_MARK_COMPACTOR:
+      return GCTracer::Scope::ScopeId::MINOR_MARK_COMPACTOR;
+    case SCAVENGER:
+      return GCTracer::Scope::ScopeId::SCAVENGER;
+  }
+  UNREACHABLE();
+}
+}  // namespace
+
 size_t Heap::PerformGarbageCollection(
     GarbageCollector collector, const v8::GCCallbackFlags gc_callback_flags) {
   DisallowJavascriptExecution no_js(isolate());
   base::Optional<SafepointScope> optional_safepoint_scope;
 
+  UpdateCurrentEpoch(collector);
+
   // Stop time-to-collection timer before safepoint - we do not want to measure
   // time for safepointing.
   collection_barrier_->StopTimeToCollectionTimer();
 
+  TRACE_GC_EPOCH(tracer(), CollectorScopeId(collector), ThreadKind::kMain);
+
   if (FLAG_local_heaps) {
     optional_safepoint_scope.emplace(this);
   }
+
 #ifdef VERIFY_HEAP
   if (FLAG_verify_heap) {
     Verify();
   }
 #endif
+
   tracer()->StartInSafepoint();
 
   GarbageCollectionPrologueInSafepoint();
@@ -2042,6 +2074,16 @@ size_t Heap::PerformGarbageCollection(
   return freed_global_handles;
 }
 
+void Heap::UpdateCurrentEpoch(GarbageCollector collector) {
+  if (IsYoungGenerationCollector(collector)) {
+    epoch_young_ = next_epoch();
+  } else if (incremental_marking()->IsStopped()) {
+    epoch_full_ = next_epoch();
+  }
+}
+
+void Heap::UpdateEpochFull() { epoch_full_ = next_epoch(); }
+
 void Heap::RecomputeLimits(GarbageCollector collector) {
   if (!((collector == MARK_COMPACTOR) ||
         (HasLowYoungGenerationAllocationRate() &&
@@ -3419,8 +3461,9 @@ void Heap::FinalizeIncrementalMarkingIncrementally(
 
   HistogramTimerScope incremental_marking_scope(
       isolate()->counters()->gc_incremental_marking_finalize());
-  TRACE_EVENT0("v8", "V8.GCIncrementalMarkingFinalize");
-  TRACE_GC(tracer(), GCTracer::Scope::MC_INCREMENTAL_FINALIZE);
+  TRACE_EVENT1("v8", "V8.GCIncrementalMarkingFinalize", "epoch", epoch_full());
+  TRACE_GC_EPOCH(tracer(), GCTracer::Scope::MC_INCREMENTAL_FINALIZE,
+                 ThreadKind::kMain);
 
   SafepointScope safepoint(this);
   InvokeIncrementalMarkingPrologueCallbacks();

src/heap/heap.h

@@ -249,6 +249,8 @@ using EphemeronRememberedSet =
     std::unordered_map<EphemeronHashTable, std::unordered_set<int>,
                        Object::Hasher>;
 
+using CollectionEpoch = uint32_t;
+
 class Heap {
  public:
   // Stores ephemeron entries where the EphemeronHashTable is in old-space,
@@ -511,6 +513,9 @@ class Heap {
 
   void NotifyOldGenerationExpansion(AllocationSpace space, MemoryChunk* chunk);
 
+  void UpdateCurrentEpoch(GarbageCollector collector);
+  void UpdateEpochFull();
+
   inline Address* NewSpaceAllocationTopAddress();
   inline Address* NewSpaceAllocationLimitAddress();
   inline Address* OldSpaceAllocationTopAddress();
@@ -1558,6 +1563,9 @@ class Heap {
 
   static Isolate* GetIsolateFromWritableObject(HeapObject object);
 
+  CollectionEpoch epoch_young() { return epoch_young_; }
+  CollectionEpoch epoch_full() { return epoch_full_; }
+
  private:
   using ExternalStringTableUpdaterCallback = String (*)(Heap* heap,
                                                         FullObjectSlot pointer);
@@ -2334,6 +2342,11 @@ class Heap {
 
   std::unique_ptr<third_party_heap::Heap> tp_heap_;
 
+  // We need two epochs, since there can be scavenges during incremental
+  // marking.
+  CollectionEpoch epoch_young_ = 0;
+  CollectionEpoch epoch_full_ = 0;
+
   // Classes in "heap" can be friends.
   friend class AlwaysAllocateScope;
   friend class ArrayBufferCollector;

src/heap/incremental-marking.cc

@@ -178,8 +178,10 @@ void IncrementalMarking::Start(GarbageCollectionReason gc_reason) {
       static_cast<int>(gc_reason));
   HistogramTimerScope incremental_marking_scope(
       counters->gc_incremental_marking_start());
-  TRACE_EVENT0("v8", "V8.GCIncrementalMarkingStart");
-  TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_INCREMENTAL_START);
+  TRACE_EVENT1("v8", "V8.GCIncrementalMarkingStart", "epoch",
+               heap_->epoch_full());
+  TRACE_GC_EPOCH(heap()->tracer(), GCTracer::Scope::MC_INCREMENTAL_START,
+                 ThreadKind::kMain);
   heap_->tracer()->NotifyIncrementalMarkingStart();
 
   start_time_ms_ = heap()->MonotonicallyIncreasingTimeInMs();
@@ -779,8 +781,9 @@ StepResult IncrementalMarking::AdvanceWithDeadline(
     StepOrigin step_origin) {
   HistogramTimerScope incremental_marking_scope(
       heap_->isolate()->counters()->gc_incremental_marking());
-  TRACE_EVENT0("v8", "V8.GCIncrementalMarking");
-  TRACE_GC(heap_->tracer(), GCTracer::Scope::MC_INCREMENTAL);
+  TRACE_EVENT1("v8", "V8.GCIncrementalMarking", "epoch", heap_->epoch_full());
+  TRACE_GC_EPOCH(heap_->tracer(), GCTracer::Scope::MC_INCREMENTAL,
+                 ThreadKind::kMain);
   DCHECK(!IsStopped());
 
   ScheduleBytesToMarkBasedOnTime(heap()->MonotonicallyIncreasingTimeInMs());

src/heap/mark-compact.cc

@@ -3115,8 +3115,8 @@ class PageEvacuationJob : public v8::JobTask {
       TRACE_GC(tracer_, evacuator->GetTracingScope());
       ProcessItems(delegate, evacuator);
     } else {
-      TRACE_GC1(tracer_, evacuator->GetBackgroundTracingScope(),
-                ThreadKind::kBackground);
+      TRACE_GC_EPOCH(tracer_, evacuator->GetBackgroundTracingScope(),
+                     ThreadKind::kBackground);
       ProcessItems(delegate, evacuator);
     }
   }
@@ -3489,7 +3489,7 @@ class PointersUpdatingJob : public v8::JobTask {
       TRACE_GC(tracer_, scope_);
       UpdatePointers(delegate);
     } else {
-      TRACE_GC1(tracer_, background_scope_, ThreadKind::kBackground);
+      TRACE_GC_EPOCH(tracer_, background_scope_, ThreadKind::kBackground);
       UpdatePointers(delegate);
     }
   }
@@ -4862,9 +4862,9 @@ class YoungGenerationMarkingJob : public v8::JobTask {
                GCTracer::Scope::MINOR_MC_MARK_PARALLEL);
       ProcessItems(delegate);
     } else {
-      TRACE_GC1(collector_->heap()->tracer(),
-                GCTracer::Scope::MINOR_MC_BACKGROUND_MARKING,
-                ThreadKind::kBackground);
+      TRACE_GC_EPOCH(collector_->heap()->tracer(),
+                     GCTracer::Scope::MINOR_MC_BACKGROUND_MARKING,
+                     ThreadKind::kBackground);
       ProcessItems(delegate);
     }
   }

src/heap/scavenger.cc

@@ -182,9 +182,9 @@ void ScavengerCollector::JobTask::Run(JobDelegate* delegate) {
              GCTracer::Scope::SCAVENGER_SCAVENGE_PARALLEL);
     ProcessItems(delegate, scavenger);
   } else {
-    TRACE_GC1(outer_->heap_->tracer(),
-              GCTracer::Scope::SCAVENGER_BACKGROUND_SCAVENGE_PARALLEL,
-              ThreadKind::kBackground);
+    TRACE_GC_EPOCH(outer_->heap_->tracer(),
+                   GCTracer::Scope::SCAVENGER_BACKGROUND_SCAVENGE_PARALLEL,
+                   ThreadKind::kBackground);
     ProcessItems(delegate, scavenger);
   }
 }

src/init/heap-symbols.h

@@ -425,6 +425,7 @@
   F(HEAP_EXTERNAL_WEAK_GLOBAL_HANDLES)               \
   F(HEAP_PROLOGUE)                                   \
   F(HEAP_PROLOGUE_SAFEPOINT)                         \
+  F(MARK_COMPACTOR)                                  \
   TOP_MC_SCOPES(F)                                   \
   F(MC_CLEAR_DEPENDENT_CODE)                         \
   F(MC_CLEAR_FLUSHABLE_BYTECODE)                     \
@@ -466,6 +467,7 @@
   F(MC_SWEEP_CODE)                                   \
   F(MC_SWEEP_MAP)                                    \
   F(MC_SWEEP_OLD)                                    \
+  F(MINOR_MARK_COMPACTOR)                            \
   F(MINOR_MC)                                        \
   F(MINOR_MC_CLEAR)                                  \
   F(MINOR_MC_CLEAR_STRING_TABLE)                     \
@@ -491,6 +493,7 @@
   F(MINOR_MC_MARKING_DEQUE)                          \
   F(MINOR_MC_RESET_LIVENESS)                         \
   F(MINOR_MC_SWEEPING)                               \
+  F(SCAVENGER)                                       \
   F(SCAVENGER_COMPLETE_SWEEP_ARRAY_BUFFERS)          \
   F(SCAVENGER_FAST_PROMOTE)                          \
   F(SCAVENGER_FREE_REMEMBERED_SET)                   \
@@ -520,4 +523,10 @@
   F(MINOR_MC_BACKGROUND_MARKING)                  \
   F(SCAVENGER_BACKGROUND_SCAVENGE_PARALLEL)
 
+#define TRACER_YOUNG_EPOCH_SCOPES(F)     \
+  F(BACKGROUND_YOUNG_ARRAY_BUFFER_SWEEP) \
+  F(MINOR_MARK_COMPACTOR)                \
+  F(SCAVENGER)                           \
+  F(SCAVENGER_BACKGROUND_SCAVENGE_PARALLEL)
+
 #endif  // V8_INIT_HEAP_SYMBOLS_H_