@Override
  public boolean isOverflowedToDisk(InternalRegion region,
      DistributedRegion.DiskPosition diskPosition) {
    return Helper.isOverflowedToDisk(this, region.getDiskRegion(), diskPosition);
  }
Abstract implementation class of RegionEntry interface. This is adds Disk support behavior

@since GemFire 3.5.1
geode-core/src/main/java/org/apache/geode/internal/cache/entries/AbstractOplogDiskRegionEntry.java