[tracing] Switch to new heap dump format.

base/trace_event/heap_profiler_event_writer.h

+// Copyright 2015 The Chromium Authors. All rights reserved.

[Primiano Tucci (use gerrit), 2017/03/09 11:47:44]

2017 :)

[DmitrySkiba, 2017/03/14 22:12:47]

Done.

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_TRACE_EVENT_HEAP_PROFILER_EVENT_WRITER_H_
+#define BASE_TRACE_EVENT_HEAP_PROFILER_EVENT_WRITER_H_
+
+#include <stddef.h>
+
+#include <memory>
+#include <string>
+#include <unordered_map>
+
+#include "base/base_export.h"
+
+/*
+  Heap profile event data format.

[Primiano Tucci (use gerrit), 2017/03/09 11:47:44]

this comment is really awesome. thanks a lot, really helped the review.

+
+  Input is:
+    1. Per allocator AllocationRegister
+    2. Per process deduplicators (for stack frames, types, strings)
+
+  Formatting event data has two steps:
+    1. Call ExportHeapDump() on allocation registers and accumulate results

[Primiano Tucci (use gerrit), 2017/03/09 11:47:44]

only have one small comment about naming: you have two "Export" functions here,
but only one really does the export, because, if I am understanding correctly,
they work kinda in a pipeline (i.e. this ExportHeapDump "exports" only to the
next ExportHeapProfileEventData().
How about calling this: SummarizeHeapDump() or AggregateHeapDump() and the next
one SerializeHeapProfiler{EventData,Dump,Snapshot} ?

[DmitrySkiba, 2017/03/14 22:12:47]

Done. Going with Export -> Serialize.

+       in ExportedHeapDumpsMap. ExportHeapDump() exports allocation register
+       as "allocators/<allocator>" dictionary outlined below; deduplicators
+       contained in MemoryDumpSessionState are used in the process.

[Primiano Tucci (use gerrit), 2017/03/09 11:47:44]

s/in the process/in this stage/

[DmitrySkiba, 2017/03/14 22:12:47]

Done.

+    2. Call ExportHeapProfileEventData() with ExportedHeapDumpsMap and
+       MemoryDumpSessionState. This puts everything together:
+       a. Entries from ExportedHeapDumpsMap are formatted as
+          "allocators/<allocator>" nodes.
+       b. Deduplicators from MemoryDumpSessionState are formatted as
+          "maps/" nodes. Deduplicators are exported incrementally using
+          their ExportIncrementally() methods.
+
+  ExportHeapDump() aggregates allocation register entries first by backtrace,
+  then by type (i.e. creates map {(backtrace, type) -> AllocationMetrics}).
+  During aggregation backtraces and types are deduplicated.
+
+  Resulting event data format:
+  {
+    "version": 1,
+
+    "allocators": {
+      <allocator>: {

[Primiano Tucci (use gerrit), 2017/03/09 11:47:44]

maybe, just to clarify, I'ld s/<allocator>/[malloc, partition_alloc, blinkgc]

[DmitrySkiba, 2017/03/14 22:12:47]

Done.

+        "nodes":  [<stack_frame_id1>, <stack_frame_id2>, ...],
+        "types":  [<type_id1>,        <type_id2>,        ...],
+        "counts": [<count1>,          <count2>,          ...],
+        "sizes":  [<size1>,           <size1>,           ...]

[Primiano Tucci (use gerrit), 2017/03/09 11:47:44]

I guess the 2nd one is size2?

[DmitrySkiba, 2017/03/14 22:12:47]

Done.

+      }
+    },
+
+    "maps": {
+      "nodes": [
+        {
+          "id": <stack_frame_id>,
+          "parent": <parent_id>,

[Primiano Tucci (use gerrit), 2017/03/09 11:47:44]

not sure if this is going to affect too much the previous discussions, so feel
free to ignore this comment.
Since we are redesigning this and there will be lot of nodes here, how about
calling the keys:
"parent" -> "p"
"name_sid" -> "s" (or "n")

that would save quite some bytes in the trace no?

[DmitrySkiba, 2017/03/14 22:12:47]

Yeah, we need to bikeshed that. We can do a pass after everything else is
settled.

[Primiano Tucci (use gerrit), 2017/03/15 20:41:40]

Alright. Agree that's definitely not a blocker for this CL.

+          "name_sid": <name_string_id>
+        },
+        ...
+      ],
+      "types": [
+        {
+          "id": <type_id>,
+          "name_sid": <name_string_id>
+        }
+      ],
+      "strings": [
+        {
+          "id": <string_id>,
+          "string": <string>
+        }
+      ]
+    }
+  }
+*/
+
+namespace base {
+namespace trace_event {
+
+class AllocationRegister;
+class MemoryDumpSessionState;
+class TracedValue;
+
+// Exports heap allocations as "allocators/<allocator>" dictionary described
+// above. Return value is supposed to be added to ExportedHeapDumpsMap map
+// and later passed to ExportHeapProfileEventData().
+BASE_EXPORT std::unique_ptr<TracedValue> ExportHeapDump(
+    const AllocationRegister& allocation_register,
+    const MemoryDumpSessionState& session_state);
+
+// Maps allocator name to its heap dump.
+using ExportedHeapDumpsMap =

[Primiano Tucci (use gerrit), 2017/03/09 11:47:44]

yeah the more I look at this the more I think that this IMHO should be
SerializedHeapDumpsMap

[DmitrySkiba, 2017/03/14 22:12:47]

Done.

+    std::unordered_map<std::string, std::unique_ptr<TracedValue>>;
+
+// Exports event data according to the format described above.
+BASE_EXPORT std::unique_ptr<TracedValue> ExportHeapProfileEventData(
+    const ExportedHeapDumpsMap& heap_dumps,
+    const MemoryDumpSessionState& session_state);
+
+}  // namespace trace_event
+}  // namespace base
+
+#endif  // BASE_TRACE_EVENT_HEAP_PROFILER_EVENT_WRITER_H_