// bump start to next page
		start = round(limit, pageSize)
	}
	return start, start + n
}

var memmap = mmap.Mmap
var munmap = mmap.Munmap

func (m *mappedFile) close() {
	m.closeOnce.Do(func() {
		if m.mapping != nil {
			munmap(m.mapping)
			m.mapping = nil
		}
		if m.f != nil {
			m.f.Close() // best effort
			m.f = nil
		}
	})
}