From: Jens Axboe <axboe@fb.com>
Date: Fri, 29 May 2015 19:10:23 +0000 (-0600)
Subject: block: only honor SG gap prevention for merges that contain data
X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=beefa6ba7bf304d3de3a02cb7366fb0a7d6b27ab;p=openwrt%2Fstaging%2Fblogic.git

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 fd3fee81c23c..30a0d9f89017 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -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];