[heap] Add histogram counters to track GC reasons.

BUG=chromium:644713
LOG=NO

Review-Url: https://codereview.chromium.org/2322453002
Cr-Commit-Position: refs/heads/master@{#39250}

src/counters.h

@@ -835,6 +835,9 @@ class RuntimeCallStats {
   HR(code_cache_reject_reason, V8.CodeCacheRejectReason, 1, 6, 6)             \
   HR(errors_thrown_per_context, V8.ErrorsThrownPerContext, 0, 200, 20)        \
   HR(debug_feature_usage, V8.DebugFeatureUsage, 1, 7, 7)                      \
+  HR(incremental_marking_reason, V8.GCIncrementalMarkingReason, 0, 21, 22)    \
+  HR(mark_compact_reason, V8.GCMarkCompactReason, 0, 21, 22)                  \
+  HR(scavenge_reason, V8.GCScavengeReason, 0, 21, 22)                         \
   /* Asm/Wasm. */                                                             \
   HR(wasm_functions_per_module, V8.WasmFunctionsPerModule, 1, 10000, 51)
 

src/heap/gc-tracer.cc

@@ -205,10 +205,17 @@ void GCTracer::Start(GarbageCollector collector,
 
   int committed_memory = static_cast<int>(heap_->CommittedMemory() / KB);
   int used_memory = static_cast<int>(current_.start_object_size / KB);
-  heap_->isolate()->counters()->aggregated_memory_heap_committed()->AddSample(
-      start_time, committed_memory);
-  heap_->isolate()->counters()->aggregated_memory_heap_used()->AddSample(
-      start_time, used_memory);
+
+  Counters* counters = heap_->isolate()->counters();
+
+  if (collector == SCAVENGER) {
+    counters->scavenge_reason()->AddSample(static_cast<int>(gc_reason));
+  } else {
+    counters->mark_compact_reason()->AddSample(static_cast<int>(gc_reason));
+  }
+  counters->aggregated_memory_heap_committed()->AddSample(start_time,
+                                                          committed_memory);
+  counters->aggregated_memory_heap_used()->AddSample(start_time, used_memory);
   // TODO(cbruni): remove once we fully moved to a trace-based system.
   if (FLAG_runtime_call_stats) {
     RuntimeCallStats::Enter(heap_->isolate()->counters()->runtime_call_stats(),

src/heap/heap.h

@@ -349,28 +349,31 @@ enum class ClearRecordedSlots { kYes, kNo };
 enum class ClearBlackArea { kYes, kNo };
 
 enum class GarbageCollectionReason {
-  kUnknown,
-  kAllocationFailure,
-  kAllocationLimit,
-  kContextDisposal,
-  kCountersExtension,
-  kDebugger,
-  kDeserializer,
-  kExternalMemoryPressure,
-  kFinalizeMarkingViaStackGuard,
-  kFinalizeMarkingViaTask,
-  kFullHashtable,
-  kHeapProfiler,
-  kIdleTask,
-  kLastResort,
-  kLowMemoryNotification,
-  kMakeHeapIterable,
-  kMemoryPressure,
-  kMemoryReducer,
-  kRuntime,
-  kSamplingProfiler,
-  kSnapshotCreator,
-  kTesting
+  kUnknown = 0,
+  kAllocationFailure = 1,
+  kAllocationLimit = 2,
+  kContextDisposal = 3,
+  kCountersExtension = 4,
+  kDebugger = 5,
+  kDeserializer = 6,
+  kExternalMemoryPressure = 7,
+  kFinalizeMarkingViaStackGuard = 8,
+  kFinalizeMarkingViaTask = 9,
+  kFullHashtable = 10,
+  kHeapProfiler = 11,
+  kIdleTask = 12,
+  kLastResort = 13,
+  kLowMemoryNotification = 14,
+  kMakeHeapIterable = 15,
+  kMemoryPressure = 16,
+  kMemoryReducer = 17,
+  kRuntime = 18,
+  kSamplingProfiler = 19,
+  kSnapshotCreator = 20,
+  kTesting = 21
+  // If you add new items here, then update the incremental_marking_reason,
+  // mark_compact_reason, and scavenge_reason counters in counters.h.
+  // Also update src/tools/metrics/histograms/histograms.xml in chromium.
 };
 
 // A queue of objects promoted during scavenge. Each object is accompanied by

src/heap/incremental-marking.cc

@@ -515,8 +515,12 @@ void IncrementalMarking::Start(GarbageCollectionReason gc_reason) {
   DCHECK(heap_->gc_state() == Heap::NOT_IN_GC);
   DCHECK(!heap_->isolate()->serializer_enabled());
 
+  Counters* counters = heap_->isolate()->counters();
+
+  counters->incremental_marking_reason()->AddSample(
+      static_cast<int>(gc_reason));
   HistogramTimerScope incremental_marking_scope(
-      heap_->isolate()->counters()->gc_incremental_marking_start());
+      counters->gc_incremental_marking_start());
   TRACE_EVENT0("v8", "V8.GCIncrementalMarkingStart");
   ResetStepCounters();
   heap_->tracer()->NotifyIncrementalMarkingStart();