[tracing] Track number of allocations in heap profiler

base/trace_event/malloc_dump_provider.cc

 // Copyright 2015 The Chromium 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 "base/trace_event/malloc_dump_provider.h"
 
 #include <stddef.h>
 
 #include "base/allocator/allocator_extension.h"
 #include "base/allocator/allocator_shim.h"
@@ skipping 160 matching lines @@
   // was enabled (--enable-heap-profiling) AND a DETAILED dump is requested.
   // However, when enabled, the overhead of the heap profiler should be always
   // reported to avoid oscillations of the malloc total in LIGHT dumps.
 
   tid_dumping_heap_ = PlatformThread::CurrentId();
   // At this point the Insert/RemoveAllocation hooks will ignore this thread.
   // Enclosing all the temporariy data structures in a scope, so that the heap
   // profiler does not see unabalanced malloc/free calls from these containers.
   {
     TraceEventMemoryOverhead overhead;
-    hash_map<AllocationContext, size_t> bytes_by_context;
+    hash_map<AllocationContext, AllocationsSizeAndCount> metrics_by_context;
     {
       AutoLock lock(allocation_register_lock_);
       if (allocation_register_) {
         if (args.level_of_detail == MemoryDumpLevelOfDetail::DETAILED) {
-          for (const auto& alloc_size : *allocation_register_)
-            bytes_by_context[alloc_size.context] += alloc_size.size;
+          for (const auto& alloc_size : *allocation_register_) {
+            metrics_by_context[alloc_size.context].size += alloc_size.size;
+            metrics_by_context[alloc_size.context].count++;

[Dmitry Skiba, 2016/04/14 19:07:30]

Let's avoid second lookup by caching result from the first one.

[Primiano Tucci (use gerrit), 2016/04/14 19:37:21]

+1. Good suggestion ;-)

[ssid, 2016/04/14 20:17:10]

Done.

+          }
         }
         allocation_register_->EstimateTraceMemoryOverhead(&overhead);
       }
     }  // lock(allocation_register_lock_)
 
-    if (!bytes_by_context.empty()) {
+    if (!metrics_by_context.empty()) {
       std::unique_ptr<TracedValue> heap_dump = ExportHeapDump(
-          bytes_by_context, pmd->session_state()->stack_frame_deduplicator(),
+          metrics_by_context, pmd->session_state()->stack_frame_deduplicator(),
           pmd->session_state()->type_name_deduplicator());
       pmd->AddHeapDump("malloc", std::move(heap_dump));
     }
     overhead.DumpInto("tracing/heap_profiler_malloc", pmd);
   }
   tid_dumping_heap_ = kInvalidThreadId;
 
   return true;
 }
 
@@ skipping 46 matching lines @@
       tid_dumping_heap_ == PlatformThread::CurrentId())
     return;
   AutoLock lock(allocation_register_lock_);
   if (!allocation_register_)
     return;
   allocation_register_->Remove(address);
 }
 
 }  // namespace trace_event
 }  // namespace base