@Override
  public long getBytesUsed() {
    if (memoryAllocator == null) {
      return 0;
    }
    return memoryAllocator.getUsedMemory();
  }
Returns the number of bytes of memory reported by the memory allocator as currently in use.
geode-core/src/main/java/org/apache/geode/internal/cache/control/OffHeapMemoryMonitor.java