dm mpath: return DM_MAPIO_REQUEUE on blk-mq rq allocation failure (050af08f) · Commits · 戴 / test

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>

drivers/md/dm-mpath.c

+13 −1

Original line number	Diff line number	Diff line
		@@ -533,7 +533,19 @@ 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;
		}

		/*
		* 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;

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