code: public long getEvitableBytes() {
      long bytes = 0;
      for (BlockMeta blockMeta : mDir.getBlocks()) {
        long blockId = blockMeta.getBlockId();
        if (mManagerView.isBlockEvictable(blockId)) {
          bytes += blockMeta.getBlockSize();
        }
      }
      return bytes;
    }
docs: Gets evictable bytes for this dir, i.e., the total bytes of total evictable blocks.
  
  @return evictable bytes for this dir