code: func JoinSubcgroup(controller string, subcgroup string) error {
  	subcgroupPath := filepath.Join("/sys/fs/cgroup", controller, subcgroup)
  	if err := os.MkdirAll(subcgroupPath, 0600); err != nil {
  		return errwrap.Wrap(fmt.Errorf("error creating %q subcgroup", subcgroup), err)
  	}
  	pidBytes := []byte(strconv.Itoa(os.Getpid()))
  	if err := ioutil.WriteFile(filepath.Join(subcgroupPath, "cgroup.procs"), pidBytes, 0600); err != nil {
  		return errwrap.Wrap(fmt.Errorf("error adding ourselves to the %q subcgroup", subcgroup), err)
  	}
  
  	return nil
  }
docs: // JoinSubcgroup makes the calling process join the subcgroup hierarchy on a
  // particular controller