[PATCH 3/5] dm-mpath: return DM_MAPIO_REQUEUE in case of rq allocation failure
From: Ming Lei <hidden>
Date: 2017-09-30 11:48:00
Also in:
dm-devel, lkml
Subsystem:
device-mapper (lvm), the rest · Maintainers:
Alasdair Kergon, Mike Snitzer, Mikulas Patocka, Benjamin Marzinski, Linus Torvalds
blk-mq will rerun queue via RESTART 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 return BLK_STS_RESOURCE to blk-mq so that dequeue from I/O scheduler can be stopped, then I/O merge gets improved. Signed-off-by: Ming Lei <redacted> --- drivers/md/dm-mpath.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 97e4bd100fa1..9ee223170ee9 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c@@ -500,8 +500,20 @@ static int multipath_clone_and_map(struct dm_target *ti, struct request *rq, if (queue_dying) { 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 to 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, + * otherwise I/O merge can be hurt. + */ + 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;
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2.9.5