1 files changed, 28 insertions, 4 deletions

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 7548f332121a..01a696b0a4d3 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1672,12 +1672,36 @@ static inline bool bios_segs_mergeable(struct request_queue *q,
         return true;
 }
 
-static inline bool bio_will_gap(struct request_queue *q, struct bio *prev,
-                         struct bio *next)
+static inline bool bio_will_gap(struct request_queue *q,
+                                struct request *prev_rq,
+                                struct bio *prev,
+                                struct bio *next)
 {
         if (bio_has_data(prev) && queue_virt_boundary(q)) {
                 struct bio_vec pb, nb;
 
+                /*
+                 * don't merge if the 1st bio starts with non-zero
+                 * offset, otherwise it is quite difficult to respect
+                 * sg gap limit. We work hard to merge a huge number of small
+                 * single bios in case of mkfs.
+                 */
+                if (prev_rq)
+                        bio_get_first_bvec(prev_rq->bio, &pb);
+                else
+                        bio_get_first_bvec(prev, &pb);
+                if (pb.bv_offset)
+                        return true;
+
+                /*
+                 * We don't need to worry about the situation that the
+                 * merged segment ends in unaligned virt boundary:
+                 *
+                 * - if 'pb' ends aligned, the merged segment ends aligned
+                 * - if 'pb' ends unaligned, the next bio must include
+                 *   one single bvec of 'nb', otherwise the 'nb' can't
+                 *   merge with 'pb'
+                 */
                 bio_get_last_bvec(prev, &pb);
                 bio_get_first_bvec(next, &nb);
 
@@ -1690,12 +1714,12 @@ static inline bool bio_will_gap(struct request_queue *q, struct bio *prev,
 
 static inline bool req_gap_back_merge(struct request *req, struct bio *bio)
 {
-        return bio_will_gap(req->q, req->biotail, bio);
+        return bio_will_gap(req->q, req, req->biotail, bio);
 }
 
 static inline bool req_gap_front_merge(struct request *req, struct bio *bio)
 {
-        return bio_will_gap(req->q, bio, req->bio);
+        return bio_will_gap(req->q, NULL, bio, req->bio);
 }
 
 int kblockd_schedule_work(struct work_struct *work);