block: return ELEVATOR_DISCARD_MERGE if possible

When merging one bio to request, if they are discard IO and the queue
supports multi-range discard, we need to return ELEVATOR_DISCARD_MERGE
because both block core and related drivers(nvme, virtio-blk) doesn't
handle mixed discard io merge(traditional IO merge together with
discard merge) well.

Fix the issue by returning ELEVATOR_DISCARD_MERGE in this situation,
so both blk-mq and drivers just need to handle multi-range discard.

Reported-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Fixes: 2705dfb20947 ("block: fix discard request merge")
Link: https://lore.kernel.org/r/20210729034226.1591070-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 1576e858d3a5f24120983c7e982e9d558449a5d2..e4a61eda2d0fce3c1de5f082787893c3a97a28ab 100644 (file)
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -2361,6 +2361,9 @@ static int bfq_request_merge(struct request_queue *q, struct request **req,
        __rq = bfq_find_rq_fmerge(bfqd, bio, q);
        if (__rq && elv_bio_merge_ok(__rq, bio)) {
                *req = __rq;
+
+               if (blk_discard_mergable(__rq))
+                       return ELEVATOR_DISCARD_MERGE;
                return ELEVATOR_FRONT_MERGE;
        }
 

diff --git a/block/blk-merge.c b/block/blk-merge.c
index a11b3b53717efe7433d449b089b982c5956edb47..f8707ff7e2fcca88b95490be4c01a99484db8164 100644 (file)
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -705,22 +705,6 @@ static void blk_account_io_merge_request(struct request *req)
        }
 }
 
-/*
- * Two cases of handling DISCARD merge:
- * If max_discard_segments > 1, the driver takes every bio
- * as a range and send them to controller together. The ranges
- * needn't to be contiguous.
- * Otherwise, the bios/requests will be handled as same as
- * others which should be contiguous.
- */
-static inline bool blk_discard_mergable(struct request *req)
-{
-       if (req_op(req) == REQ_OP_DISCARD &&
-           queue_max_discard_segments(req->q) > 1)
-               return true;
-       return false;
-}
-
 static enum elv_merge blk_try_req_merge(struct request *req,
                                        struct request *next)
 {

diff --git a/block/elevator.c b/block/elevator.c
index 9beaafd238e06f46a53af7dc53963fbdf816ac4b..ff45d8388f48775910248593e6f114e1376a02e5 100644 (file)
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -336,6 +336,9 @@ enum elv_merge elv_merge(struct request_queue *q, struct request **req,
        __rq = elv_rqhash_find(q, bio->bi_iter.bi_sector);
        if (__rq && elv_bio_merge_ok(__rq, bio)) {
                *req = __rq;
+
+               if (blk_discard_mergable(__rq))
+                       return ELEVATOR_DISCARD_MERGE;
                return ELEVATOR_BACK_MERGE;
        }
 

diff --git a/block/mq-deadline-main.c b/block/mq-deadline-main.c
index 6f612e6dc82b6e165f804267d167857be863d8a4..294be0c0db65d6a34547bffb3edd810faa50da41 100644 (file)
--- a/block/mq-deadline-main.c
+++ b/block/mq-deadline-main.c
@@ -677,6 +677,8 @@ static int dd_request_merge(struct request_queue *q, struct request **rq,
 
                if (elv_bio_merge_ok(__rq, bio)) {
                        *rq = __rq;
+                       if (blk_discard_mergable(__rq))
+                               return ELEVATOR_DISCARD_MERGE;
                        return ELEVATOR_FRONT_MERGE;
                }
        }

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 23e1253a8d88882caf5fbda979ff4084dd3a35b7..07eef02325b4f62e61187a6a52eee8fb3269e050 100644 (file)
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1519,6 +1519,22 @@ static inline int queue_limit_discard_alignment(struct queue_limits *lim, sector
        return offset << SECTOR_SHIFT;
 }
 
+/*
+ * Two cases of handling DISCARD merge:
+ * If max_discard_segments > 1, the driver takes every bio
+ * as a range and send them to controller together. The ranges
+ * needn't to be contiguous.
+ * Otherwise, the bios/requests will be handled as same as
+ * others which should be contiguous.
+ */
+static inline bool blk_discard_mergable(struct request *req)
+{
+       if (req_op(req) == REQ_OP_DISCARD &&
+           queue_max_discard_segments(req->q) > 1)
+               return true;
+       return false;
+}
+
 static inline int bdev_discard_alignment(struct block_device *bdev)
 {
        struct request_queue *q = bdev_get_queue(bdev);