[heap] Relax condition for forced finalization of incremental marking.

src/heap/heap.h

 // Copyright 2012 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_HEAP_H_
 #define V8_HEAP_HEAP_H_
 
 #include <cmath>
 #include <map>
 
@@ skipping 1805 matching lines @@
   // ===========================================================================
   // GC statistics. ============================================================
   // ===========================================================================
 
   inline size_t OldGenerationSpaceAvailable() {
     if (old_generation_allocation_limit_ <= PromotedTotalSize()) return 0;
     return old_generation_allocation_limit_ -
            static_cast<size_t>(PromotedTotalSize());
   }
 
+  // We allow incremental marking to overshoot the allocation limit for
+  // performace reasons. If the overshoot is too large then we are more
+  // eager to finalize incremental marking.
+  inline bool AllocationLimitOvershotByLargeMargin() {
+    if (old_generation_allocation_limit_ >= PromotedTotalSize()) return false;
+    uint64_t overshoot = PromotedTotalSize() - old_generation_allocation_limit_;
+    // Overshoot margin is 50% of allocation limit or half-way to the max heap.
+    uint64_t margin =
+        Min(old_generation_allocation_limit_ / 2,
+            (max_old_generation_size_ - old_generation_allocation_limit_) / 2);
+    return overshoot >= margin;
+  }
+
   void UpdateTotalGCTime(double duration);
 
   bool MaximumSizeScavenge() { return maximum_size_scavenges_ > 0; }
 
   // ===========================================================================
   // Growing strategy. =========================================================
   // ===========================================================================
 
   // Decrease the allocation limit if the new limit based on the given
   // parameters is lower than the current limit.
@@ skipping 813 matching lines @@
   friend class LargeObjectSpace;
   friend class NewSpace;
   friend class PagedSpace;
   DISALLOW_COPY_AND_ASSIGN(AllocationObserver);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_HEAP_H_