[Tracing] Integrate GC object statistics with tracing.

src/heap/mark-compact.cc

 // Copyright 2012 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/mark-compact.h"
 
 #include "src/base/atomicops.h"
 #include "src/base/bits.h"
 #include "src/base/sys-info.h"
 #include "src/code-stubs.h"
@@ skipping 2224 matching lines @@
   while (space_it.has_next()) {
     std::unique_ptr<ObjectIterator> it(space_it.next()->GetObjectIterator());
     ObjectIterator* obj_it = it.get();
     while ((obj = obj_it->Next()) != nullptr) {
       visitor->Visit(obj);
     }
   }
 }
 
 void MarkCompactCollector::RecordObjectStats() {
   if (FLAG_track_gc_object_stats) {

[ssid, 2016/09/29 21:45:31]

I thought you wanted to enable this flag when tracing is enabled? Was it not
possible?

[lpy, 2016/09/29 22:45:42]

currently I don't think we can do that, but my plan is to have another iteration
on it to make these flags work with tracing.

[fmeawad, 2016/09/30 00:44:05]

Add a comment in the CL description that to test this, please enable the flag

[lpy, 2016/09/30 18:21:58]

Done.

     ObjectStatsVisitor visitor(heap(), heap()->live_object_stats_,
                                heap()->dead_object_stats_);
     VisitAllObjects(&visitor);
+    std::stringstream live, dead;
+    heap()->live_object_stats_->Dump(live);
+    heap()->dead_object_stats_->Dump(dead);
+    TRACE_EVENT_INSTANT2(TRACE_DISABLED_BY_DEFAULT("v8.gc_stats"),

[ssid, 2016/09/29 21:45:31]

Do we really need a new category? can we just use "v8.gc"?

[lpy, 2016/09/29 22:45:42]

We can use v8.gc, but, v8.gc will add a bunch of other trace events, which will
bring too many overhead, I want to avoid it.

[fmeawad, 2016/09/30 00:44:05]

I think gc_stats is fine.
But I wonder if TRACE_EVENT_INSTANT is the right choice here. I am OK with it
for now.

[lpy, 2016/09/30 18:21:58]

Acknowledged.

+                         "V8.GC_Objects_Stats", TRACE_EVENT_SCOPE_THREAD,
+                         "live", TRACE_STR_COPY(live.str().c_str()), "dead",
+                         TRACE_STR_COPY(dead.str().c_str()));
     if (FLAG_trace_gc_object_stats) {
       heap()->live_object_stats_->PrintJSON("live");
       heap()->dead_object_stats_->PrintJSON("dead");
     }
     heap()->live_object_stats_->CheckpointObjectStats();
     heap()->dead_object_stats_->ClearObjectStats();
   }
 }
 
 void MarkCompactCollector::MarkLiveObjects() {
@@ skipping 1739 matching lines @@
       // The target is always in old space, we don't have to record the slot in
       // the old-to-new remembered set.
       DCHECK(!heap()->InNewSpace(target));
       RecordRelocSlot(host, &rinfo, target);
     }
   }
 }
 
 }  // namespace internal
 }  // namespace v8