[heap] Add histogram counters to track GC reasons.

src/heap/gc-tracer.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/heap/gc-tracer.h"
 
 #include "src/counters.h"
 #include "src/heap/heap-inl.h"
 #include "src/isolate.h"
 
@@ skipping 187 matching lines @@
       cumulative_incremental_marking_bytes_;
   current_.cumulative_pure_incremental_marking_duration =
       cumulative_pure_incremental_marking_duration_;
 
   for (int i = 0; i < Scope::NUMBER_OF_SCOPES; i++) {
     current_.scopes[i] = 0;
   }
 
   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(),
                             &timer_, &RuntimeCallStats::GC);
   }
   // TODO(lpy): Add a tracing equivalent for the runtime call stats.
 }
 
 void GCTracer::MergeBaseline(const Event& baseline) {
   current_.incremental_marking_bytes =
@@ skipping 605 matching lines @@
 }
 
 void GCTracer::ResetSurvivalEvents() { recorded_survival_ratios_.Reset(); }
 
 void GCTracer::NotifyIncrementalMarkingStart() {
   incremental_marking_start_time_ = heap_->MonotonicallyIncreasingTimeInMs();
 }
 
 }  // namespace internal
 }  // namespace v8