block: improve the gap check in __bio_add_pc_page

If we can add more data into an existing segment we do not create a gap
per definition, so move the check for a gap after the attempt to merge
into the segment.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 7 insertions, 7 deletions

diff --git a/block/bio.c b/block/bio.c
index 54769659a434..537d71a30e56 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -710,18 +710,18 @@ static int __bio_add_pc_page(struct request_queue *q, struct bio *bio,
                         goto done;
                 }
 
-                /*
-                 * If the queue doesn't support SG gaps and adding this
-                 * offset would create a gap, disallow it.
-                 */
-                if (bvec_gap_to_prev(q, bvec, offset))
-                        return 0;
-
                 if (page_is_mergeable(bvec, page, len, offset, &same_page) &&
                     can_add_page_to_seg(q, bvec, page, len, offset)) {
                         bvec->bv_len += len;
                         goto done;
                 }
+
+                /*
+                 * If the queue doesn't support SG gaps and adding this segment
+                 * would create a gap, disallow it.
+                 */
+                if (bvec_gap_to_prev(q, bvec, offset))
+                        return 0;
         }
 
         if (bio_full(bio, len))