Add mode to reduce memory usage in idle notification.

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

 // 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.
 
 #ifndef V8_HEAP_GC_IDLE_TIME_HANDLER_H_
 #define V8_HEAP_GC_IDLE_TIME_HANDLER_H_
 
 #include "src/globals.h"
 
 namespace v8 {
 namespace internal {
 
 enum GCIdleTimeActionType {
   DONE,
   DO_NOTHING,
   DO_INCREMENTAL_MARKING,
   DO_SCAVENGE,
   DO_FULL_GC,
   DO_FINALIZE_SWEEPING
 };
 
 
 class GCIdleTimeAction {
  public:
   static GCIdleTimeAction Done() {
     GCIdleTimeAction result;
     result.type = DONE;
     result.parameter = 0;
     result.additional_work = false;
+    result.reduce_memory = false;
     return result;
   }
 
   static GCIdleTimeAction Nothing() {
     GCIdleTimeAction result;
     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;
   }
 
   static GCIdleTimeAction Scavenge() {
     GCIdleTimeAction result;
     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;
   }
 
   static GCIdleTimeAction FinalizeSweeping() {
     GCIdleTimeAction result;
     result.type = DO_FINALIZE_SWEEPING;
     result.parameter = 0;
     result.additional_work = false;
+    result.reduce_memory = false;
     return result;
   }
 
   void Print();
 
   GCIdleTimeActionType type;
   intptr_t parameter;
   bool additional_work;
+  bool reduce_memory;
 };
 
 
 class GCTracer;
 
 // The idle time handler makes decisions about which garbage collection
 // operations are executing during IdleNotification.
 class GCIdleTimeHandler {
  public:
   // If we haven't recorded any incremental marking events yet, we carefully
@@ skipping 16 matching lines @@
   static const size_t kInitialConservativeFinalIncrementalMarkCompactSpeed =
       2 * MB;
 
   // Maximum mark-compact time returned by EstimateMarkCompactTime.
   static const size_t kMaxMarkCompactTimeInMs;
 
   // Maximum final incremental mark-compact time returned by
   // 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;
 
   // The maximum idle time when frames are rendered is 16.66ms.
   static const size_t kMaxFrameRenderingIdleTime = 17;
 
   // We conservatively assume that in the next kTimeUntilNextIdleEvent ms
   // no idle notification happens.
   static const size_t kTimeUntilNextIdleEvent = 100;
 
   // If we haven't recorded any scavenger events yet, we use a conservative
   // lower bound for the scavenger speed.
   static const size_t kInitialConservativeScavengeSpeed = 100 * KB;
 
   // If contexts are disposed at a higher rate a full gc is triggered.
   static const double kHighContextDisposalRate;
 
   // Incremental marking step time.
   static const size_t kIncrementalMarkingStepTimeInMs = 1;
 
   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;
+
+  // Mutator is considered idle if
+  // 1) there is an idle notification with time >= kLargeLongIdleTime,
+  // 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 kLargeLongIdleTime = 900;
+  static const int kLongIdleNotificationsBeforeMutatorIsIdle = 20;
+
 
   class HeapState {
    public:
     void Print();
 
     int contexts_disposed;
     double contexts_disposal_rate;
     size_t size_of_objects;
     bool incremental_marking_stopped;
     bool can_start_incremental_marking;
     bool sweeping_in_progress;
     bool sweeping_completed;
     size_t mark_compact_speed_in_bytes_per_ms;
     size_t incremental_marking_speed_in_bytes_per_ms;
     size_t final_incremental_mark_compact_speed_in_bytes_per_ms;
     size_t scavenge_speed_in_bytes_per_ms;
     size_t used_new_space_size;
     size_t new_space_capacity;
     size_t new_space_allocation_throughput_in_bytes_per_ms;
   };
 
   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);
 
   static size_t EstimateMarkCompactTime(
       size_t size_of_objects, size_t mark_compact_speed_in_bytes_per_ms);
 
   static size_t EstimateFinalIncrementalMarkCompactTime(
       size_t size_of_objects, size_t mark_compact_speed_in_bytes_per_ms);
 
   static bool ShouldDoMarkCompact(size_t idle_time_in_ms,
                                   size_t size_of_objects,
                                   size_t mark_compact_speed_in_bytes_per_ms);
 
   static bool ShouldDoContextDisposalMarkCompact(int context_disposed,
                                                  double contexts_disposal_rate);
 
   static bool ShouldDoFinalIncrementalMarkCompact(
       size_t idle_time_in_ms, size_t size_of_objects,
       size_t final_incremental_mark_compact_speed_in_bytes_per_ms);
 
   static bool ShouldDoOverApproximateWeakClosure(size_t idle_time_in_ms);
 
   static bool ShouldDoScavenge(
       size_t idle_time_in_ms, size_t new_space_size, size_t used_new_space_size,
       size_t scavenger_speed_in_bytes_per_ms,
       size_t new_space_allocation_throughput_in_bytes_per_ms);
 
+  enum Mode { kReduceLatency, kReduceMemory, kDone };
+
+  Mode mode() { return mode_; }
+
  private:
-  GCIdleTimeAction NothingOrDone();
+  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);
 
-  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 idle_mark_compacts_;
+  int mark_compacts_;
+  int scavenges_;
+  // The number of long idle notifications with no mutator GC happening
+  // between the notifications.
+  int long_idle_notifications_;
 
-  int mark_compacts_since_idle_round_started_;
-  int scavenges_since_last_idle_round_;
-  int idle_times_which_made_no_progress_since_last_idle_round_;
+  Mode mode_;
 
   DISALLOW_COPY_AND_ASSIGN(GCIdleTimeHandler);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_GC_IDLE_TIME_HANDLER_H_