Let marking speed depend on the actual incremental write barrier count.

src/incremental-marking.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
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@@ skipping 863 matching lines @@
 
   if (state_ == MARKING && no_marking_scope_depth_ > 0) return;
 
   // The marking speed is driven either by the allocation rate or by the rate
   // at which we are having to check the color of objects in the write barrier.
   // It is possible for a tight non-allocating loop to run a lot of write
   // barriers before we get here and check them (marking can only take place on
   // allocation), so to reduce the lumpiness we don't use the write barriers
   // invoked since last step directly to determine the amount of work to do.
   intptr_t bytes_to_process =
-      marking_speed_ * Max(allocated_, kWriteBarriersInvokedThreshold);
+      marking_speed_ * Max(allocated_, write_barriers_invoked_since_last_step_);
   allocated_ = 0;
   write_barriers_invoked_since_last_step_ = 0;
 
   bytes_scanned_ += bytes_to_process;
 
   double start = 0;
 
   if (FLAG_trace_incremental_marking || FLAG_trace_gc) {
     start = OS::TimeCurrentMillis();
   }
@@ skipping 99 matching lines @@
   bytes_scanned_ = 0;
   write_barriers_invoked_since_last_step_ = 0;
 }
 
 
 int64_t IncrementalMarking::SpaceLeftInOldSpace() {
   return heap_->MaxOldGenerationSize() - heap_->PromotedSpaceSizeOfObjects();
 }
 
 } }  // namespace v8::internal