code: def _unmount_devicemapper(self, cid):
          
          mountpoint = self.mountpoint
          Mount.unmount_path(mountpoint)
  
          cinfo = self.client.inspect_container(cid)
          dev_name = cinfo['GraphDriver']['Data']['DeviceName']
  
          Mount.remove_thin_device(dev_name)
          self._cleanup_container(cinfo)
docs: Devicemapper unmount backend.