[PATCH] block: don't check position contiguity for DISCARD in attempt_merge

[PATCH] block: don't check position contiguity for DISCARD in attempt_merge

[Jianchao Wang]

Discard command supports multiple ranges of blocks, so needn't
checking position contiguity when merging. Let's do the same thing
in attempt_merge as the blk_try_merge.

Signed-off-by: Jianchao Wang <jianchao.w.wang@oracle.com>
---
 block/blk-merge.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 42a4674..c94749b 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -732,9 +732,10 @@ static struct request *attempt_merge(struct request_queue *q,
 		return NULL;
 
 	/*
-	 * not contiguous
+	 * not contiguous, except for DISCARD
 	 */
-	if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
+	if ((req_op(req) != REQ_OP_DISCARD) &&
+	    (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next)))
 		return NULL;
 
 	if (rq_data_dir(req) != rq_data_dir(next)
-- 
2.7.4

Re: [PATCH] block: don't check position contiguity for DISCARD in attempt_merge

[Ming Lei]

On Fri, Oct 19, 2018 at 5:23 PM Jianchao Wang
<jianchao.w.wang@oracle.com> wrote:
>
> Discard command supports multiple ranges of blocks, so needn't
> checking position contiguity when merging. Let's do the same thing
> in attempt_merge as the blk_try_merge.
>
> Signed-off-by: Jianchao Wang <jianchao.w.wang@oracle.com>
> ---
>  block/blk-merge.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index 42a4674..c94749b 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -732,9 +732,10 @@ static struct request *attempt_merge(struct request_queue *q,
>                 return NULL;
>
>         /*
> -        * not contiguous
> +        * not contiguous, except for DISCARD
>          */
> -       if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
> +       if ((req_op(req) != REQ_OP_DISCARD) &&
> +           (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next)))
>                 return NULL;
>
>         if (rq_data_dir(req) != rq_data_dir(next)
> --
> 2.7.4
>
Reviewed-by: Ming Lei <ming.lei@redhat.com>

Thanks,
Ming Lei

Re: [PATCH] block: don't check position contiguity for DISCARD in attempt_merge

[Martin K. Petersen]

Jianchao,

> Discard command supports multiple ranges of blocks, so needn't
> checking position contiguity when merging. Let's do the same thing
> in attempt_merge as the blk_try_merge.

Discards need to be contiguous unless queue->limits.max_discard_segments
is bigger than 1. So if you remove this I think you need to add a
contiguity check in req_attempt_discard_merge().

-- 
Martin K. Petersen	Oracle Linux Engineering

Re: [PATCH] block: don't check position contiguity for DISCARD in attempt_merge

[jianchao.wang]

Hi Martin

On 10/19/18 11:57 PM, Martin K. Petersen wrote:
> 
> Jianchao,
> 
>> Discard command supports multiple ranges of blocks, so needn't
>> checking position contiguity when merging. Let's do the same thing
>> in attempt_merge as the blk_try_merge.
> 
> Discards need to be contiguous unless queue->limits.max_discard_segments
> is bigger than 1. So if you remove this I think you need to add a
> contiguity check in req_attempt_discard_merge().
> 
Yes.

I will send the V2 version next.

Thanks
Jianchao