Add mode to reduce memory usage in idle notification.

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

Index: src/heap/gc-idle-time-handler.h
diff --git a/src/heap/gc-idle-time-handler.h b/src/heap/gc-idle-time-handler.h
index ed89b8bc770a07aac81313ddc21ce8487c67565d..2b622c251cadc091663d8d421f910d2d33da7684 100644
--- a/src/heap/gc-idle-time-handler.h
+++ b/src/heap/gc-idle-time-handler.h
@@ -27,6 +27,7 @@ class GCIdleTimeAction {
     result.type = DONE;
     result.parameter = 0;
     result.additional_work = false;
+    result.reduce_memory = false;
     return result;
   }
 
@@ -35,14 +36,17 @@ class GCIdleTimeAction {
     result.type = DO_NOTHING;
     result.parameter = 0;
     result.additional_work = false;
+    result.reduce_memory = false;
     return result;
   }
 
-  static GCIdleTimeAction IncrementalMarking(intptr_t step_size) {
+  static GCIdleTimeAction IncrementalMarking(intptr_t step_size,
+                                             bool reduce_memory) {
     GCIdleTimeAction result;
     result.type = DO_INCREMENTAL_MARKING;
     result.parameter = step_size;
     result.additional_work = false;
+    result.reduce_memory = reduce_memory;
     return result;
   }
 
@@ -51,14 +55,18 @@ class GCIdleTimeAction {
     result.type = DO_SCAVENGE;
     result.parameter = 0;
     result.additional_work = false;
+    // TODO(ulan): add reduce_memory argument and shrink new space size if
+    // reduce_memory = true.
+    result.reduce_memory = false;
     return result;
   }
 
-  static GCIdleTimeAction FullGC() {
+  static GCIdleTimeAction FullGC(bool reduce_memory) {
     GCIdleTimeAction result;
     result.type = DO_FULL_GC;
     result.parameter = 0;
     result.additional_work = false;
+    result.reduce_memory = reduce_memory;
     return result;
   }
 
@@ -67,6 +75,7 @@ class GCIdleTimeAction {
     result.type = DO_FINALIZE_SWEEPING;
     result.parameter = 0;
     result.additional_work = false;
+    result.reduce_memory = false;
     return result;
   }
 
@@ -75,6 +84,7 @@ class GCIdleTimeAction {
   GCIdleTimeActionType type;
   intptr_t parameter;
   bool additional_work;
+  bool reduce_memory;
 };
 
 
@@ -111,13 +121,6 @@ class GCIdleTimeHandler {
   // EstimateFinalIncrementalMarkCompactTime.
   static const size_t kMaxFinalIncrementalMarkCompactTimeInMs;
 
-  // Number of idle mark-compact events, after which idle handler will finish
-  // idle round.
-  static const int kMaxMarkCompactsInIdleRound;
-
-  // Number of scavenges that will trigger start of new idle round.
-  static const int kIdleScavengeThreshold;
-
   // This is the maximum scheduled idle time. Note that it can be more than
   // 16.66 ms when there is currently no rendering going on.
   static const size_t kMaxScheduledIdleTime = 50;
@@ -141,10 +144,22 @@ class GCIdleTimeHandler {
 
   static const size_t kMinTimeForOverApproximatingWeakClosureInMs;
 
-  // Number of times we will return a Nothing action per Idle round despite
-  // having idle time available before we returning a Done action to ensure we
-  // don't keep scheduling idle tasks and making no progress.
-  static const int kMaxNoProgressIdleTimesPerIdleRound = 10;
+  // The number of idle MarkCompact GCs to perform before transitioning to
+  // the kDone mode.
+  static const int kMaxIdleMarkCompacts = 3;
+
+  // The number of mutator GCs before transitioning to the kReduceLatency mode.
+  static const int kGCsBeforeMutatorIsActive = 7;

[Erik Corry, 2015/05/05 21:38:52]

These 7 GCs will normally be scavenges, so we are talking about 7x8Mbytes of
newspace allocation.  Perhaps we could make this be in terms of Mbytes
allocated, not GCs.  That way, if we experiment with different newspace sizes we
are not simultaneously making big changes to the heuristics around oldspace
collection timing.

[ulan, 2015/05/06 09:47:19]

Good idea! We could replace the scavenges_ and mark_compacts_ counters with one
allocation counter (in new and old space). Deriving that counter from the
new-space size and the size of promoted objects is not straightforward. Let me
think about that.

[Erik Corry, 2015/05/06 09:57:29]

Perhaps set the limit to 50Mbytes, and every time we do a GC we increase the
counter by the current size of a semispace.  It's approximate, but roughly
right, and pretty simple.

[Hannes Payer (out of office), 2015/05/07 08:21:52]

We know the promoted size, why not take this counter and accumulate?

[ulan, 2015/05/07 10:33:30]

We can either use new space committed size, new space live size, or promoted
size. I will experiments to see what is better.

Erik, Hannes, are ok with landing this CL now to make experimenting easier?

+
+  // Mutator is considered idle if
+  // 1) there is an idle notification with time >= kMaxLongIdleTime,
+  // 2) or there are kLongIdleNotificationsBeforeMutatorIsIdle idle
+  // notifications
+  //    with time >= kMinLongIdleTime and without any mutator GC in between.
+  static const int kMinLongIdleTime = kMaxFrameRenderingIdleTime + 1;
+  static const int kMaxLongIdleTime = 1000;
+  static const int kLongIdleNotificationsBeforeMutatorIsIdle = 20;
+
 
   class HeapState {
    public:
@@ -167,23 +182,19 @@ class GCIdleTimeHandler {
   };
 
   GCIdleTimeHandler()
-      : mark_compacts_since_idle_round_started_(0),
-        scavenges_since_last_idle_round_(0),
-        idle_times_which_made_no_progress_since_last_idle_round_(0) {}
+      : idle_mark_compacts_(0),
+        mark_compacts_(0),
+        scavenges_(0),
+        long_idle_notifications_(0),
+        mode_(kReduceLatency) {}
 
   GCIdleTimeAction Compute(double idle_time_in_ms, HeapState heap_state);
 
-  void NotifyIdleMarkCompact() {
-    if (mark_compacts_since_idle_round_started_ < kMaxMarkCompactsInIdleRound) {
-      ++mark_compacts_since_idle_round_started_;
-      if (mark_compacts_since_idle_round_started_ ==
-          kMaxMarkCompactsInIdleRound) {
-        scavenges_since_last_idle_round_ = 0;
-      }
-    }
-  }
+  void NotifyIdleMarkCompact() { ++idle_mark_compacts_; }
 
-  void NotifyScavenge() { ++scavenges_since_last_idle_round_; }
+  void NotifyMarkCompact() { ++mark_compacts_; }
+
+  void NotifyScavenge() { ++scavenges_; }
 
   static size_t EstimateMarkingStepSize(size_t idle_time_in_ms,
                                         size_t marking_speed_in_bytes_per_ms);
@@ -213,23 +224,22 @@ class GCIdleTimeHandler {
       size_t new_space_allocation_throughput_in_bytes_per_ms);
 
  private:
-  GCIdleTimeAction NothingOrDone();
-
-  void StartIdleRound() {
-    mark_compacts_since_idle_round_started_ = 0;
-    idle_times_which_made_no_progress_since_last_idle_round_ = 0;
-  }
-  bool IsMarkCompactIdleRoundFinished() {
-    return mark_compacts_since_idle_round_started_ ==
-           kMaxMarkCompactsInIdleRound;
-  }
-  bool EnoughGarbageSinceLastIdleRound() {
-    return scavenges_since_last_idle_round_ >= kIdleScavengeThreshold;
-  }
-
-  int mark_compacts_since_idle_round_started_;
-  int scavenges_since_last_idle_round_;
-  int idle_times_which_made_no_progress_since_last_idle_round_;
+  enum Mode { kReduceLatency, kReduceMemory, kDone };
+
+  bool IsMutatorActive(int contexts_disposed, int gcs);
+  bool IsMutatorIdle(int long_idle_notifications, int gcs);
+  void UpdateCounters(double idle_time_in_ms);
+  void ResetCounters();
+  Mode NextMode(const HeapState& heap_state);
+  GCIdleTimeAction Action(double idle_time_in_ms, const HeapState& heap_state,
+                          bool reduce_memory);
+
+  int idle_mark_compacts_;
+  int mark_compacts_;
+  int scavenges_;
+  int long_idle_notifications_;
+
+  Mode mode_;
 
   DISALLOW_COPY_AND_ASSIGN(GCIdleTimeHandler);
 };