code: func (f *freelist) copyall(dst []pgid) {
  	m := make(pgids, 0, f.pending_count())
  	for _, list := range f.pending {
  		m = append(m, list...)
  	}
  	sort.Sort(m)
  	mergepgids(dst, f.ids, m)
  }
docs: // copyall copies into dst a list of all free ids and all pending ids in one sorted list.
  // f.count returns the minimum length required for dst.