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 <[email protected]> Fixes: 6ac45aeb6bca(block: avoid to merge splitted bio) Cc: [email protected] (v4.3+) Cc: Ming Lei <[email protected]> Cc: Jens Axboe <[email protected]> Cc: Neil Brown <[email protected]> Signed-off-by: Shaohua Li <[email protected]> --- 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
