block: Check for gaps on front and back merges

We are checking for gaps to previous bio_vec, which can
only detect back merges gaps. Moreover, at the point where
we check for a gap, we don't know if we will attempt a back
or a front merge. Thus, check for gap to prev in a back merge
attempt and check for a gap to next in a front merge attempt.

Signed-off-by: Jens Axboe <axboe@fb.com>
[sagig: Minor rename change]
Signed-off-by: Sagi Grimberg <sagig@mellanox.com>

diff --git a/block/blk-merge.c b/block/blk-merge.c
index cce23ba1ae5fdd29c936454f11981c818228829c..d9eddbc189f564308b9ed1f11d5d8226d74e62c0 100644 (file)
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -438,6 +438,8 @@ no_merge:
 int ll_back_merge_fn(struct request_queue *q, struct request *req,
                     struct bio *bio)
 {
+       if (req_gap_back_merge(req, bio))
+               return 0;
        if (blk_rq_sectors(req) + bio_sectors(bio) >
            blk_rq_get_max_sectors(req)) {
                req->cmd_flags |= REQ_NOMERGE;
@@ -456,6 +458,9 @@ int ll_back_merge_fn(struct request_queue *q, struct request *req,
 int ll_front_merge_fn(struct request_queue *q, struct request *req,
                      struct bio *bio)
 {
+
+       if (req_gap_front_merge(req, bio))
+               return 0;
        if (blk_rq_sectors(req) + bio_sectors(bio) >
            blk_rq_get_max_sectors(req)) {
                req->cmd_flags |= REQ_NOMERGE;
@@ -482,14 +487,6 @@ static bool req_no_special_merge(struct request *req)
        return !q->mq_ops && req->special;
 }
 
-static int req_gap_to_prev(struct request *req, struct bio *next)
-{
-       struct bio *prev = req->biotail;
-
-       return bvec_gap_to_prev(req->q, &prev->bi_io_vec[prev->bi_vcnt - 1],
-                       next->bi_io_vec[0].bv_offset);
-}
-
 static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
                                struct request *next)
 {
@@ -504,7 +501,7 @@ static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
        if (req_no_special_merge(req) || req_no_special_merge(next))
                return 0;
 
-       if (req_gap_to_prev(req, next->bio))
+       if (req_gap_back_merge(req, next->bio))
                return 0;
 
        /*
@@ -712,10 +709,6 @@ bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
            !blk_write_same_mergeable(rq->bio, bio))
                return false;
 
-       /* Only check gaps if the bio carries data */
-       if (bio_has_data(bio) && req_gap_to_prev(rq, bio))
-               return false;
-
        return true;
 }
 

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index a622f270f09e78fce0bf06a73de65827ef4fddf7..2ff94def041e2b211686f9e30db26dceb43c4a19 100644 (file)
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1368,6 +1368,26 @@ static inline bool bvec_gap_to_prev(struct request_queue *q,
                ((bprv->bv_offset + bprv->bv_len) & queue_virt_boundary(q));
 }
 
+static inline bool bio_will_gap(struct request_queue *q, struct bio *prev,
+                        struct bio *next)
+{
+       if (!bio_has_data(prev))
+               return false;
+
+       return bvec_gap_to_prev(q, &prev->bi_io_vec[prev->bi_vcnt - 1],
+                               next->bi_io_vec[0].bv_offset);
+}
+
+static inline bool req_gap_back_merge(struct request *req, struct bio *bio)
+{
+       return bio_will_gap(req->q, 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);
+}
+
 struct work_struct;
 int kblockd_schedule_work(struct work_struct *work);
 int kblockd_schedule_delayed_work(struct delayed_work *dwork, unsigned long delay);