Limit rate of full garbage collections triggered by idle notification.

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

 // Copyright 2014 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/gc-idle-time-handler.h"
 #include "src/heap/gc-tracer.h"
 #include "src/utils.h"
 
 namespace v8 {
 namespace internal {
@@ skipping 134 matching lines @@
         idle_time_in_ms) {
       return true;
     }
   }
   return false;
 }
 
 
 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);
 }
 
 
 bool GCIdleTimeHandler::ShouldDoContextDisposalMarkCompact(
     int contexts_disposed, double contexts_disposal_rate) {
   return contexts_disposed > 0 && contexts_disposal_rate > 0 &&
          contexts_disposal_rate < kHighContextDisposalRate;
 }
 
 
@@ skipping 56 matching lines @@
   }
 
   if (IsMarkCompactIdleRoundFinished()) {
     if (EnoughGarbageSinceLastIdleRound()) {
       StartIdleRound();
     } else {
       return GCIdleTimeAction::Done();
     }
   }
 
   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.
       // TODO(ulan): Once we enable code compaction for incremental marking, we
       // can get rid of this special case and always start incremental marking.
       int remaining_mark_sweeps =
           kMaxMarkCompactsInIdleRound - mark_compacts_since_idle_round_started_;
       if (static_cast<size_t>(idle_time_in_ms) > kMaxScheduledIdleTime &&
           (remaining_mark_sweeps <= 2 ||
            !heap_state.can_start_incremental_marking)) {
@@ skipping 14 matching lines @@
       !heap_state.can_start_incremental_marking) {
     return GCIdleTimeAction::Nothing();
   }
   size_t step_size = EstimateMarkingStepSize(
       static_cast<size_t>(kIncrementalMarkingStepTimeInMs),
       heap_state.incremental_marking_speed_in_bytes_per_ms);
   return GCIdleTimeAction::IncrementalMarking(step_size);
 }
 }
 }