From: Shaohua Li <shli@fb.com>
Date: Mon, 25 Apr 2016 23:52:38 +0000 (-0700)
Subject: MD: make bio mergeable
X-Git-Tag: firefly_0821_release~176^2~4^2~46^2~46
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=f3b51a03bea6dc4cda740481d48b2ff49abdced5;p=firefly-linux-kernel-4.4.55.git

MD: make bio mergeable

commit 9c573de3283af007ea11c17bde1e4568d9417328 upstream.

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-and-tested-by: Park Ju Hyung <qkrwngud825@gmail.com>
Fixes: 6ac45aeb6bca(block: avoid to merge splitted bio)
Cc: Ming Lei <ming.lei@canonical.com>
Cc: Neil Brown <neilb@suse.de>
Reviewed-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/drivers/md/md.c b/drivers/md/md.c
index b1e1f6b95782..c57fdf847b47 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -293,6 +293,8 @@ 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();