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dm mpath: return DM_MAPIO_REQUEUE on blk-mq rq allocation failure

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blk-mq will rerun queue via RESTART or dispatch wake after one request
is completed, so not necessary to wait random time for requeuing, we
should trust blk-mq to do it.

More importantly, we need to return BLK_STS_RESOURCE to blk-mq so that
dequeuing from the I/O scheduler can be stopped, this results in
improved I/O merging.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
This commit is contained in:
Ming Lei 2018-01-11 14:01:56 +08:00 committed by Mike Snitzer
parent 4b259fc4a8
commit 050af08ffb
1 changed files with 13 additions and 1 deletions
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14
drivers/md/dm-mpath.c
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@ -533,8 +533,20 @@ static int multipath_clone_and_map(struct dm_target *ti, struct request *rq,
if (blk_queue_dying(q)) {
atomic_inc(&m->pg_init_in_progress);
activate_or_offline_path(pgpath);
return DM_MAPIO_DELAY_REQUEUE;
}
return DM_MAPIO_DELAY_REQUEUE;
/*
* blk-mq's SCHED_RESTART can cover this requeue, so we
* needn't deal with it by DELAY_REQUEUE. More importantly,
* we have to return DM_MAPIO_REQUEUE so that blk-mq can
* get the queue busy feedback (via BLK_STS_RESOURCE),
* otherwise I/O merging can suffer.
*/
if (q->mq_ops)
return DM_MAPIO_REQUEUE;
else
return DM_MAPIO_DELAY_REQUEUE;
}
clone->bio = clone->biotail = NULL;
clone->rq_disk = bdev->bd_disk;