code: func (fs *FileSet) bytes() int {
  	var b int
  	for _, level := range fs.levels {
  		b += int(unsafe.Sizeof(level))
  	}
  	// Do not count SeriesFile because it belongs to the code that constructed this FileSet.
  	for _, file := range fs.files {
  		b += file.bytes()
  	}
  	b += int(unsafe.Sizeof(*fs))
  	return b
  }
docs: // bytes estimates the memory footprint of this FileSet, in bytes.