heap/api: EmbedderHeapTracer: Pass along memory reducing mode

Change-Id: I55e8e42b88c8df1f75ff05f22b39d69e9dc586ce
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1588457
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61097}

include/v8.h

@@ -7171,6 +7171,11 @@ enum class MemoryPressureLevel { kNone, kModerate, kCritical };
  */
 class V8_EXPORT EmbedderHeapTracer {
  public:
+  enum class TraceFlags : uint64_t {
+    kNoFlags = 0,
+    kReduceMemory = 1 << 0,
+  };
+
   // Indicator for the stack state of the embedder.
   enum EmbedderStackState {
     kUnknown,
@@ -7209,7 +7214,8 @@ class V8_EXPORT EmbedderHeapTracer {
   /**
    * Called at the beginning of a GC cycle.
    */
-  virtual void TracePrologue() = 0;
+  V8_DEPRECATE_SOON("Use version with flags.", virtual void TracePrologue()) {}
+  virtual void TracePrologue(TraceFlags flags);
 
   /**
    * Called to advance tracing in the embedder.
@@ -7283,6 +7289,18 @@ class V8_EXPORT EmbedderHeapTracer {
   friend class internal::LocalEmbedderHeapTracer;
 };
 
+constexpr EmbedderHeapTracer::TraceFlags operator&(
+    EmbedderHeapTracer::TraceFlags lhs, EmbedderHeapTracer::TraceFlags rhs) {
+  return static_cast<EmbedderHeapTracer::TraceFlags>(
+      static_cast<uint64_t>(lhs) & static_cast<uint64_t>(rhs));
+}
+
+constexpr EmbedderHeapTracer::TraceFlags operator|(
+    EmbedderHeapTracer::TraceFlags lhs, EmbedderHeapTracer::TraceFlags rhs) {
+  return static_cast<EmbedderHeapTracer::TraceFlags>(
+      static_cast<uint64_t>(lhs) | static_cast<uint64_t>(rhs));
+}
+
 /**
  * Callback and supporting data used in SnapshotCreator to implement embedder
  * logic to serialize internal fields.

src/api.cc

@@ -10502,6 +10502,17 @@ void Testing::DeoptimizeAll(Isolate* isolate) {
   i::Deoptimizer::DeoptimizeAll(i_isolate);
 }
 
+void EmbedderHeapTracer::TracePrologue(TraceFlags flags) {
+#if __clang__
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdeprecated"
+#endif
+  TracePrologue();
+#if __clang__
+#pragma clang diagnostic pop
+#endif
+}
+
 void EmbedderHeapTracer::FinalizeTracing() {
   if (isolate_) {
     i::Isolate* isolate = reinterpret_cast<i::Isolate*>(isolate_);

src/heap/embedder-tracing.cc

@@ -19,12 +19,13 @@ void LocalEmbedderHeapTracer::SetRemoteTracer(EmbedderHeapTracer* tracer) {
     remote_tracer_->isolate_ = reinterpret_cast<v8::Isolate*>(isolate_);
 }
 
-void LocalEmbedderHeapTracer::TracePrologue() {
+void LocalEmbedderHeapTracer::TracePrologue(
+    EmbedderHeapTracer::TraceFlags flags) {
   if (!InUse()) return;
 
   num_v8_marking_worklist_was_empty_ = 0;
   embedder_worklist_empty_ = false;
-  remote_tracer_->TracePrologue();
+  remote_tracer_->TracePrologue(flags);
 }
 
 void LocalEmbedderHeapTracer::TraceEpilogue() {

src/heap/embedder-tracing.h

@@ -48,7 +48,7 @@ class V8_EXPORT_PRIVATE LocalEmbedderHeapTracer final {
   EmbedderHeapTracer* remote_tracer() const { return remote_tracer_; }
 
   void SetRemoteTracer(EmbedderHeapTracer* tracer);
-  void TracePrologue();
+  void TracePrologue(EmbedderHeapTracer::TraceFlags flags);
   void TraceEpilogue();
   void EnterFinalPause();
   bool Trace(double deadline);

src/heap/heap.cc

@@ -4813,6 +4813,12 @@ EmbedderHeapTracer* Heap::GetEmbedderHeapTracer() const {
   return local_embedder_heap_tracer()->remote_tracer();
 }
 
+EmbedderHeapTracer::TraceFlags Heap::flags_for_embedder_tracer() const {
+  if (ShouldReduceMemory())
+    return EmbedderHeapTracer::TraceFlags::kReduceMemory;
+  return EmbedderHeapTracer::TraceFlags::kNoFlags;
+}
+
 void Heap::RegisterExternallyReferencedObject(Address* location) {
   // The embedder is not aware of whether numbers are materialized as heap
   // objects are just passed around as Smis.

src/heap/heap.h

@@ -936,6 +936,8 @@ class Heap {
   void SetEmbedderStackStateForNextFinalizaton(
       EmbedderHeapTracer::EmbedderStackState stack_state);
 
+  EmbedderHeapTracer::TraceFlags flags_for_embedder_tracer() const;
+
   // ===========================================================================
   // External string table API. ================================================
   // ===========================================================================

src/heap/incremental-marking.cc

@@ -385,7 +385,8 @@ void IncrementalMarking::StartMarking() {
     // marking (including write barriers) is fully set up.
     TRACE_GC(heap()->tracer(),
              GCTracer::Scope::MC_INCREMENTAL_EMBEDDER_PROLOGUE);
-    heap_->local_embedder_heap_tracer()->TracePrologue();
+    heap_->local_embedder_heap_tracer()->TracePrologue(
+        heap_->flags_for_embedder_tracer());
   }
 }
 

src/heap/mark-compact.cc

@@ -796,7 +796,8 @@ void MarkCompactCollector::Prepare() {
 
   if (!was_marked_incrementally_) {
     TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_MARK_EMBEDDER_PROLOGUE);
-    heap_->local_embedder_heap_tracer()->TracePrologue();
+    heap_->local_embedder_heap_tracer()->TracePrologue(
+        heap_->flags_for_embedder_tracer());
   }
 
   // Don't start compaction if we are in the middle of incremental

test/cctest/heap/test-embedder-tracing.cc

@@ -69,7 +69,7 @@ class TestEmbedderHeapTracer final : public v8::EmbedderHeapTracer {
 
   bool IsTracingDone() final { return to_register_with_v8_.empty(); }
 
-  void TracePrologue() final {
+  void TracePrologue(EmbedderHeapTracer::TraceFlags) final {
     if (prologue_behavior_ == TracePrologueBehavior::kCallV8WriteBarrier) {
       auto local = array_.Get(isolate());
       local->Set(local->CreationContext(), 0, v8::Object::New(isolate()))

test/unittests/heap/embedder-tracing-unittest.cc

@@ -31,7 +31,7 @@ LocalEmbedderHeapTracer::WrapperInfo CreateWrapperInfo() {
 
 class MockEmbedderHeapTracer : public EmbedderHeapTracer {
  public:
-  MOCK_METHOD0(TracePrologue, void());
+  MOCK_METHOD1(TracePrologue, void(EmbedderHeapTracer::TraceFlags));
   MOCK_METHOD0(TraceEpilogue, void());
   MOCK_METHOD1(EnterFinalPause, void(EmbedderHeapTracer::EmbedderStackState));
   MOCK_METHOD0(IsTracingDone, bool());
@@ -52,7 +52,7 @@ TEST(LocalEmbedderHeapTracer, NoRemoteTracer) {
   // We should be able to call all functions without a remote tracer being
   // attached.
   EXPECT_FALSE(local_tracer.InUse());
-  local_tracer.TracePrologue();
+  local_tracer.TracePrologue(EmbedderHeapTracer::TraceFlags::kNoFlags);
   local_tracer.EnterFinalPause();
   bool done = local_tracer.Trace(std::numeric_limits<double>::infinity());
   EXPECT_TRUE(done);
@@ -63,8 +63,17 @@ TEST(LocalEmbedderHeapTracer, TracePrologueForwards) {
   StrictMock<MockEmbedderHeapTracer> remote_tracer;
   LocalEmbedderHeapTracer local_tracer(nullptr);
   local_tracer.SetRemoteTracer(&remote_tracer);
-  EXPECT_CALL(remote_tracer, TracePrologue());
-  local_tracer.TracePrologue();
+  EXPECT_CALL(remote_tracer, TracePrologue(_));
+  local_tracer.TracePrologue(EmbedderHeapTracer::TraceFlags::kNoFlags);
+}
+
+TEST(LocalEmbedderHeapTracer, TracePrologueForwardsMemoryReducingFlag) {
+  StrictMock<MockEmbedderHeapTracer> remote_tracer;
+  LocalEmbedderHeapTracer local_tracer(nullptr);
+  local_tracer.SetRemoteTracer(&remote_tracer);
+  EXPECT_CALL(remote_tracer,
+              TracePrologue(EmbedderHeapTracer::TraceFlags::kReduceMemory));
+  local_tracer.TracePrologue(EmbedderHeapTracer::TraceFlags::kReduceMemory);
 }
 
 TEST(LocalEmbedderHeapTracer, TraceEpilogueForwards) {