code: void addCache(Path hdfsPath, Path localPath, long size) throws IOException {
      assert size == new File(localPath.toString()).length();
      assert size == fs.getFileStatus(hdfsPath).getLen();
      lookasideCache.addCache(hdfsPath, localPath, size);
    }
docs: Insert a file into the cache. If the cache is exceeding capacity,
  then this call can, in turn, call backinto evictCache().