code: func (c *Container) unmapRun() {
  	if !c.mapped {
  		return
  	}
  	runs := c.runs()
  	tmp := make([]interval16, c.len)
  	copy(tmp, runs)
  	h := (*reflect.SliceHeader)(unsafe.Pointer(&tmp))
  	c.pointer, c.cap = (*uint16)(unsafe.Pointer(h.Data)), int32(h.Cap)
  	c.mapped = false
  }
docs: // unmapRun ensures that the container is not using mmapped storage.