From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:48374 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751781AbdIVBf1 (ORCPT ); Thu, 21 Sep 2017 21:35:27 -0400 From: Ming Lei To: dm-devel@redhat.com, Mike Snitzer , Jens Axboe Cc: linux-block@vger.kernel.org, Christoph Hellwig , Bart Van Assche , Laurence Oberman , Ming Lei Subject: [PATCH] dm-mpath: return DM_MAPIO_REQUEUE in case of rq allocation failure Date: Fri, 22 Sep 2017 09:35:06 +0800 Message-Id: <20170922013506.22510-1-ming.lei@redhat.com> Sender: linux-block-owner@vger.kernel.org List-Id: linux-block@vger.kernel.org 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 --- 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 11f273d2f018..0902f7762306 100644 --- a/drivers/md/dm-mpath.c +++ b/drivers/md/dm-mpath.c @@ -504,8 +504,20 @@ 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; -- 2.9.5