An object should only be promoted to the old generation if it survived a scavenge operation.

src/heap-inl.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_INL_H_
 #define V8_HEAP_INL_H_
 
 #include <cmath>
 
 #include "src/heap.h"
@@ skipping 284 matching lines @@
 }
 
 
 bool Heap::OldGenerationAllocationLimitReached() {
   if (!incremental_marking()->IsStopped()) return false;
   return OldGenerationSpaceAvailable() < 0;
 }
 
 
 bool Heap::ShouldBePromoted(Address old_address, int object_size) {
-  // An object should be promoted if:
-  // - the object has survived a scavenge operation or
-  // - to space is already 25% full.
+  // An object should be promoted if the object has survived a
+  // scavenge operation.
   NewSpacePage* page = NewSpacePage::FromAddress(old_address);
   Address age_mark = new_space_.age_mark();
-  bool below_mark = page->IsFlagSet(MemoryChunk::NEW_SPACE_BELOW_AGE_MARK) &&
+  return page->IsFlagSet(MemoryChunk::NEW_SPACE_BELOW_AGE_MARK) &&
       (!page->ContainsLimit(age_mark) || old_address < age_mark);
-  return below_mark || (new_space_.Size() + object_size) >=
-                        (new_space_.EffectiveCapacity() >> 2);
 }
 
 
 void Heap::RecordWrite(Address address, int offset) {
   if (!InNewSpace(address)) store_buffer_.Mark(address + offset);
 }
 
 
 void Heap::RecordWrites(Address address, int start, int len) {
   if (!InNewSpace(address)) {
@@ skipping 401 matching lines @@
 
 
 double GCTracer::SizeOfHeapObjects() {
   return (static_cast<double>(heap_->SizeOfObjects())) / MB;
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HEAP_INL_H_