[heap] Simplify heuristics for incremental step size.

src/heap/incremental-marking.h

Index: src/heap/incremental-marking.h
diff --git a/src/heap/incremental-marking.h b/src/heap/incremental-marking.h
index 0ba0f2ce5331734656fbf1e5f0e2717c263d7d90..34332b00f3f2198fa3338872c372b195693def7d 100644
--- a/src/heap/incremental-marking.h
+++ b/src/heap/incremental-marking.h
@@ -123,16 +123,12 @@ class IncrementalMarking {
   // heavy (color-checking) write barriers have been invoked.
   static const intptr_t kAllocatedThreshold = 65536;
   static const intptr_t kWriteBarriersInvokedThreshold = 32768;
-  // Start off by marking this many times more memory than has been allocated.
-  static const intptr_t kInitialMarkingSpeed = 1;
-  // But if we are promoting a lot of data we need to mark faster to keep up
-  // with the data that is entering the old space through promotion.
-  static const intptr_t kFastMarking = 3;
-  // After this many steps we increase the marking/allocating factor.
-  static const intptr_t kMarkingSpeedAccellerationInterval = 1024;
-  // This is how much we increase the marking/allocating factor by.
-  static const intptr_t kMarkingSpeedAccelleration = 2;
-  static const intptr_t kMaxMarkingSpeed = 1000;
+  // Cap the write barrier counter to avoid overflows.
+  static const intptr_t kMaxWriteBarrierCounter = 1 << 20;
+  // These constants are arbitrary and chosen based on benchmarks.
+  static const intptr_t kBytesToMarkPerAllocatedByte = 3;
+  static const intptr_t kBytesToMarkPerWriteBarrier = 10;
+  static const intptr_t kMinIncrementalStepDurationInMs = 1;
 
   // This is the upper bound for how many times we allow finalization of
   // incremental marking to be postponed.
@@ -187,8 +183,6 @@ class IncrementalMarking {
 
   void ActivateGeneratedStub(Code* stub);
 
-  void NotifyOfHighPromotionRate();
-
   void NotifyIncompleteScanOfObject(int unscanned_bytes) {
     unscanned_bytes_of_large_object_ = unscanned_bytes;
   }
@@ -255,8 +249,6 @@ class IncrementalMarking {
 
   int64_t SpaceLeftInOldSpace();
 
-  void SpeedUp();
-
   void ResetStepCounters();
 
   void StartMarking();
@@ -301,13 +293,7 @@ class IncrementalMarking {
   State state_;
   bool is_compacting_;
 
-  int steps_count_;
-  int64_t old_generation_space_available_at_start_of_incremental_;
-  int64_t old_generation_space_used_at_start_of_incremental_;
-  int64_t bytes_rescanned_;
   bool should_hurry_;
-  int marking_speed_;
-  intptr_t bytes_scanned_;
   intptr_t allocated_;
   intptr_t write_barriers_invoked_since_last_step_;
   size_t idle_marking_delay_counter_;