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>
diff --git a/block/blk-merge.c b/block/blk-merge.c
index fd3fee8..30a0d9f 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -589,7 +589,8 @@
!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];