[PATCH] block: consider discard merge last

[PATCH] block: consider discard merge last

[Keith Busch]

From: Keith Busch <kbusch@kernel.org>

If the next discard range is contiguous with the current range being
considered, it's cheaper to expand the current range than to append an
additional bio.

Signed-off-by: Keith Busch <kbusch@kernel.org>
---
 block/blk-merge.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index d3115d7469df0..db08bc9060916 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -712,10 +712,10 @@ static void blk_account_io_merge_request(struct request *req)
 static enum elv_merge blk_try_req_merge(struct request *req,
 					struct request *next)
 {
-	if (blk_discard_mergable(req))
-		return ELEVATOR_DISCARD_MERGE;
-	else if (blk_rq_pos(req) + blk_rq_sectors(req) == blk_rq_pos(next))
+	if (blk_rq_pos(req) + blk_rq_sectors(req) == blk_rq_pos(next))
 		return ELEVATOR_BACK_MERGE;
+	else if (blk_discard_mergable(req))
+		return ELEVATOR_DISCARD_MERGE;
 
 	return ELEVATOR_NO_MERGE;
 }
@@ -903,12 +903,12 @@ bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
 
 enum elv_merge blk_try_merge(struct request *rq, struct bio *bio)
 {
-	if (blk_discard_mergable(rq))
-		return ELEVATOR_DISCARD_MERGE;
-	else if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
+	if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
 		return ELEVATOR_BACK_MERGE;
 	else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
 		return ELEVATOR_FRONT_MERGE;
+	else if (blk_discard_mergable(rq))
+		return ELEVATOR_DISCARD_MERGE;
 	return ELEVATOR_NO_MERGE;
 }
 
-- 
2.47.3

Re: [PATCH] block: consider discard merge last

[Chaitanya Kulkarni]

On 11/14/25 10:31, Keith Busch wrote:
> From: Keith Busch<kbusch@kernel.org>
>
> If the next discard range is contiguous with the current range being
> considered, it's cheaper to expand the current range than to append an
> additional bio.
>
> Signed-off-by: Keith Busch<kbusch@kernel.org>

Looks good.

Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>

-ck

Re: [PATCH] block: consider discard merge last

[Jens Axboe]

On Fri, 14 Nov 2025 10:31:45 -0800, Keith Busch wrote:
> If the next discard range is contiguous with the current range being
> considered, it's cheaper to expand the current range than to append an
> additional bio.
> 
> 

Applied, thanks!

[1/1] block: consider discard merge last
      commit: 2516c246d01c23a5f5310e9ac78d9f8aad9b1d0e

Best regards,
-- 
Jens Axboe