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block: only honor SG gap prevention for merges that contain data 

We can safely merge anything that wont generate an SG list entry,
so if the bio is data-less (discard), don't look at potential
SG gaps.

Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Jens Axboe 2015-05-29 13:10:23 -06:00
parent f6454b049d
commit beefa6ba7b
1 changed files with 2 additions and 1 deletions
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3
block/blk-merge.c
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@ -589,7 +589,8 @@ bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
!blk_write_same_mergeable(rq->bio, bio))
return false;
if (q->queue_flags & (1 << QUEUE_FLAG_SG_GAPS)) {
/* Only check gaps if the bio carries data */
if (q->queue_flags & (1 << QUEUE_FLAG_SG_GAPS) && bio_has_data(bio)) {
struct bio_vec *bprev;
bprev = &rq->biotail->bi_io_vec[rq->biotail->bi_vcnt - 1];