Limit rate of full garbage collections triggered by idle notification.

src/heap/gc-idle-time-handler.cc

Index: src/heap/gc-idle-time-handler.cc
diff --git a/src/heap/gc-idle-time-handler.cc b/src/heap/gc-idle-time-handler.cc
index c74b46ea9b6d126b0770df551a830593198d63ef..b572ca2527de57a13cd8aa960c30830dda2ac76c 100644
--- a/src/heap/gc-idle-time-handler.cc
+++ b/src/heap/gc-idle-time-handler.cc
@@ -152,10 +152,15 @@ bool GCIdleTimeHandler::ShouldDoScavenge(
 
 bool GCIdleTimeHandler::ShouldDoMarkCompact(
     size_t idle_time_in_ms, size_t size_of_objects,
-    size_t mark_compact_speed_in_bytes_per_ms) {
-  return idle_time_in_ms >=
-         EstimateMarkCompactTime(size_of_objects,
-                                 mark_compact_speed_in_bytes_per_ms);
+    size_t mark_compact_speed_in_bytes_per_ms,
+    size_t last_mark_compact_time_in_ms, size_t current_time_in_ms) {
+  bool mark_compact_rate_high =
+      current_time_in_ms <
+      last_mark_compact_time_in_ms + kMinTimeInBetweenMarkCompactsInMs;
+  return (!mark_compact_rate_high || idle_time_in_ms > kMaxScheduledIdleTime) &&
+         idle_time_in_ms >=
+             EstimateMarkCompactTime(size_of_objects,

[rmcilroy, 2015/03/20 14:56:08]

this is looking pretty complex condition now - could you pull each of these out
into seperate well-named variables like mark_compact_rate_high

+                                     mark_compact_speed_in_bytes_per_ms);
 }
 
 
@@ -233,9 +238,10 @@ GCIdleTimeAction GCIdleTimeHandler::Compute(double idle_time_in_ms,
   }
 
   if (heap_state.incremental_marking_stopped) {

[Erik Corry, 2015/03/20 15:21:27]

It feels like we are piling more and more heuristics on.  Does anyone understand
the current system?

It looks like the bit above ("IsMarkCompactIdleRoundFinished") will run 7 GCs in
the idle time, and then not start another until we have allocated enough garbage
or there has been a context disposal.  That would seem to be plenty of GCs.  Why
do we need more than that?

-    if (ShouldDoMarkCompact(static_cast<size_t>(idle_time_in_ms),
-                            heap_state.size_of_objects,
-                            heap_state.mark_compact_speed_in_bytes_per_ms)) {
+    if (ShouldDoMarkCompact(
+            static_cast<size_t>(idle_time_in_ms), heap_state.size_of_objects,
+            heap_state.mark_compact_speed_in_bytes_per_ms,
+            heap_state.last_mark_compact_time, heap_state.current_time)) {
       // If there are no more than two GCs left in this idle round and we are
       // allowed to do a full GC, then make those GCs full in order to compact
       // the code space.