Add GCTracer metrics for a scavenger GC for DOM wrappers

src/global-handles.cc

Index: src/global-handles.cc
diff --git a/src/global-handles.cc b/src/global-handles.cc
index f5850da04d5b940e46cba8e171bff52e3afeefd3..68eb5785d9f248ee0b94e99410d3d108384d61af 100644
--- a/src/global-handles.cc
+++ b/src/global-handles.cc
@@ -552,7 +552,7 @@ void GlobalHandles::IterateNewSpaceWeakIndependentRoots(ObjectVisitor* v) {
 
 
 bool GlobalHandles::PostGarbageCollectionProcessing(
-    GarbageCollector collector) {
+    GarbageCollector collector, GCTracer* tracer) {

[Michael Starzinger, 2012/11/16 13:45:51]

I am kind of hesitant to let the GCTracer "escape" into the global handles
subsystem. Is it important for the measurements to have per GC-cycle counts?

If not, then I would suggest to use normal per-isolate counters instead (i.e.
v8-counters.h) to gather those numbers.

I wouldn't use histograms though, because apparently they are automatically
exposed via UMA and these plain measurements are not useful when aggregated over
all pages and all users.

[haraken, 2012/11/19 07:45:43]

I think yes. What I am interested in is how many global handles are
disposed/copied/promoted in each scavenger/full GC.
Then how about adding a couple of methods to global-handles.cc and having
GCTracer count up numbers in Heap::PerformGarbageCollection()?
Agreed. I am not interested in UMAs for these metrics.

   // Process weak global handle callbacks. This must be done after the
   // GC is completely done, because the callbacks may invoke arbitrary
   // API functions.
@@ -602,10 +602,17 @@ bool GlobalHandles::PostGarbageCollectionProcessing(
   for (int i = 0; i < new_space_nodes_.length(); ++i) {
     Node* node = new_space_nodes_[i];
     ASSERT(node->is_in_new_space_list());
-    if (node->IsRetainer() && isolate_->heap()->InNewSpace(node->object())) {
-      new_space_nodes_[last++] = node;
+    if (node->IsRetainer()) {
+      if (isolate_->heap()->InNewSpace(node->object())) {
+        new_space_nodes_[last++] = node;
+        tracer->increment_copied_nodes_in_new_space();
+      } else {
+        node->set_in_new_space_list(false);
+        tracer->increment_promoted_nodes();
+      }
     } else {
       node->set_in_new_space_list(false);
+      tracer->increment_died_nodes_in_new_space();
     }
   }
   new_space_nodes_.Rewind(last);