On Thu, Aug 03, 2017 at 05:33:13PM +0000, Bart Van Assche wrote:

Are you aware that the SCSI core already keeps track of the number of busy requests
per LUN? See also the device_busy member of struct scsi_device. How about giving the
block layer core access in some way to that counter?

I'd love ot move it to blk-mq in a scalable way eventually, as
we'll run into the same problems with NVMe systems with multiple
namespaces.