linux-kernel - [PATCH] MD: make bio mergeable

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Date:	Mon, 25 Apr 2016 16:52:38 -0700
From:	Shaohua Li <shli@...com>
To:	<linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-raid@...r.kernel.org>
CC:	<qkrwngud825@...il.com>, <Kernel-team@...com>,
	"v4.3+" <stable@...r.kernel.org>,
	Ming Lei <ming.lei@...onical.com>, Jens Axboe <axboe@...com>,
	Neil Brown <neilb@...e.de>
Subject: [PATCH] MD: make bio mergeable

blk_queue_split marks bio unmergeable, which makes sense for normal bio.
But if dispatching the bio to underlayer disk, the blk_queue_split
checks are invalid, hence it's possible the bio becomes mergeable.

In the reported bug, this bug causes trim against raid0 performance slash
https://bugzilla.kernel.org/show_bug.cgi?id=117051

Reported-by: Park Ju Hyung <qkrwngud825@...il.com>
Fixes: 6ac45aeb6bca(block: avoid to merge splitted bio)
Cc: stable@...r.kernel.org (v4.3+)
Cc: Ming Lei <ming.lei@...onical.com>
Cc: Jens Axboe <axboe@...com>
Cc: Neil Brown <neilb@...e.de>
Signed-off-by: Shaohua Li <shli@...com>
---
 drivers/md/md.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 194580f..14d3b37 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -284,6 +284,8 @@ static blk_qc_t md_make_request(struct request_queue *q, struct bio *bio)
 	 * go away inside make_request
 	 */
 	sectors = bio_sectors(bio);
+	/* bio could be mergeable after passing to underlayer */
+	bio->bi_rw &= ~REQ_NOMERGE;
 	mddev->pers->make_request(mddev, bio);
 
 	cpu = part_stat_lock();
-- 
2.8.0.rc2