On 04/05/2021 07:17, Hannes Reinecke wrote:

On 5/4/21 5:20 AM, Bart Van Assche wrote:

quoted

On 5/3/21 8:03 AM, Hannes Reinecke wrote:

quoted

These commands are set aside before allocating the block-mq tag bitmap,
so they'll never show up as busy in the tag map.

That doesn't sound correct to me. Should the above perhaps be changed
into "blk_mq_start_request() is never called for internal commands so
they'll never show up as busy in the tag map"?

Yes, will do.

So why don't these - or shouldn't these - turn up in the busy tag map?

One of the motivations to use these block requests for internal commands 
is that we can take advantage of the block layer handling for CPU 
hotplug for MQ hosts, i.e. if blk-mq can't see these are inflight, then 
they would be missed in blk_mq_hctx_notify_offline() -> 
blk_mq_hctx_has_requests(), right? And who knows what else...

Thanks,
John