[PATCH 1/3] block: improve the gap check in __bio_add_pc_page

[Christoph Hellwig]

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 <h...@lst.de>
Reviewed-by: Johannes Thumshirn <jthumsh...@suse.de>
---
 block/bio.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 24a496f5d2e2..9f80bf4531b3 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))
-- 
2.20.1