Idle old generation limit is used when allocation rate is low.

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 2117 matching lines @@
   void SelectScavengingVisitorsTable();
 
   bool HasLowAllocationRate(size_t allocaion_rate);
 
   void ReduceNewSpaceSize(size_t allocaion_rate);
 
   bool TryFinalizeIdleIncrementalMarking(
       double idle_time_in_ms, size_t size_of_objects,
       size_t mark_compact_speed_in_bytes_per_ms);
 
-  GCIdleTimeHandler::HeapState ComputeHeapState(bool reduce_memory);
+  GCIdleTimeHandler::HeapState ComputeHeapState();
 
   bool PerformIdleTimeAction(GCIdleTimeAction action,
                              GCIdleTimeHandler::HeapState heap_state,
                              double deadline_in_ms,
                              bool is_long_idle_notification);
 
   void IdleNotificationEpilogue(GCIdleTimeAction action,
                                 GCIdleTimeHandler::HeapState heap_state,
                                 double start_ms, double deadline_in_ms,
                                 bool is_long_idle_notification);
@@ skipping 547 matching lines @@
   DisallowHeapAllocation no_allocation;  // i.e. no gc allowed.
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PathTracer);
 };
 #endif  // DEBUG
 }
 }  // namespace v8::internal
 
 #endif  // V8_HEAP_HEAP_H_