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* [PATCH V2] block: fix the DISCARD request merge
@ 2018-10-20 14:29 Jianchao Wang
  2018-10-22  9:00 ` Christoph Hellwig
  2018-10-22  9:06 ` Ming Lei
  0 siblings, 2 replies; 6+ messages in thread
From: Jianchao Wang @ 2018-10-20 14:29 UTC (permalink / raw)
  To: axboe; +Cc: martin.petersen, tom.leiming, hch, linux-block, linux-kernel

There are two cases when handle DISCARD merge
 - max_discard_segments == 1
   bios need to be contiguous
 - max_discard_segments > 1
   Only nvme right now. It takes every bio as a range and different
   range needn't to be contiguous.

But now, attempt_merge screws this up. It always consider contiguity
for DISCARD for the case max_discard_segments > 1 and cannot merge
contiguous DISCARD for the case max_discard_segments == 1, because
rq_attempt_discard_merge always returns false in this case.
This patch fixes both of the two cases above.

Signed-off-by: Jianchao Wang <jianchao.w.wang@oracle.com>
---

V2:
  - Add max_discard_segments > 1 checking in attempt_merge
  - Change patch title and comment
  - Add more comment in attempt_merge

 block/blk-merge.c | 24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 42a4674..8f22374 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -734,8 +734,15 @@ static struct request *attempt_merge(struct request_queue *q,
 	/*
 	 * not contiguous
 	 */
-	if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
-		return NULL;
+	if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next)) {
+		/*
+		 * When max_discard_segments is bigger than 1 (only nvme right
+		 * now), needn't consider the contiguity.
+		 */
+		if (!(req_op(req) == REQ_OP_DISCARD &&
+		      queue_max_discard_segments(q) > 1))
+			return NULL;
+	}
 
 	if (rq_data_dir(req) != rq_data_dir(next)
 	    || req->rq_disk != next->rq_disk
@@ -757,10 +764,17 @@ static struct request *attempt_merge(struct request_queue *q,
 	 * If we are allowed to merge, then append bio list
 	 * from next to rq and release next. merge_requests_fn
 	 * will have updated segment counts, update sector
-	 * counts here. Handle DISCARDs separately, as they
-	 * have separate settings.
+	 * counts here.
+	 * Two cases of Handling DISCARD:
+	 *  - max_discard_segments == 1
+	 *    The bios need to be contiguous.
+	 *  - max_discard_segments > 1
+	 *    Only nvme right now. It takes every bio as a
+	 *    range and send them to controller together. The ranges
+	 *    needn't to be contiguous.
 	 */
-	if (req_op(req) == REQ_OP_DISCARD) {
+	if (req_op(req) == REQ_OP_DISCARD &&
+	    queue_max_discard_segments(q) > 1) {
 		if (!req_attempt_discard_merge(q, req, next))
 			return NULL;
 	} else if (!ll_merge_requests_fn(q, req, next))
-- 
2.7.4


^ permalink raw reply related	[flat|nested] 6+ messages in thread
* Re: [PATCH V2] block: fix the DISCARD request merge
  2018-10-20 14:29 [PATCH V2] block: fix the DISCARD request merge Jianchao Wang
@ 2018-10-22  9:00 ` Christoph Hellwig
  2018-10-22 10:13   ` jianchao.wang
  2018-10-22  9:06 ` Ming Lei
  1 sibling, 1 reply; 6+ messages in thread
From: Christoph Hellwig @ 2018-10-22  9:00 UTC (permalink / raw)
  To: Jianchao Wang
  Cc: axboe, martin.petersen, tom.leiming, hch, linux-block, linux-kernel

On Sat, Oct 20, 2018 at 10:29:37PM +0800, Jianchao Wang wrote:
> There are two cases when handle DISCARD merge
>  - max_discard_segments == 1
>    bios need to be contiguous
>  - max_discard_segments > 1
>    Only nvme right now. It takes every bio as a range and different
>    range needn't to be contiguous.
> 
> But now, attempt_merge screws this up. It always consider contiguity
> for DISCARD for the case max_discard_segments > 1 and cannot merge
> contiguous DISCARD for the case max_discard_segments == 1, because
> rq_attempt_discard_merge always returns false in this case.
> This patch fixes both of the two cases above.
> 
> Signed-off-by: Jianchao Wang <jianchao.w.wang@oracle.com>
> ---
> 
> V2:
>   - Add max_discard_segments > 1 checking in attempt_merge
>   - Change patch title and comment
>   - Add more comment in attempt_merge
> 
>  block/blk-merge.c | 24 +++++++++++++++++++-----
>  1 file changed, 19 insertions(+), 5 deletions(-)
> 
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index 42a4674..8f22374 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -734,8 +734,15 @@ static struct request *attempt_merge(struct request_queue *q,
>  	/*
>  	 * not contiguous
>  	 */
> -	if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
> -		return NULL;
> +	if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next)) {
> +		/*
> +		 * When max_discard_segments is bigger than 1 (only nvme right
> +		 * now), needn't consider the contiguity.
> +		 */
> +		if (!(req_op(req) == REQ_OP_DISCARD &&
> +		      queue_max_discard_segments(q) > 1))
> +			return NULL;

Why not:

		if (req_op(req) != REQ_OP_DISCARD ||
		    queue_max_discard_segments(q) == 1)

which would be a lot more obvious?

> +	 * counts here.
> +	 * Two cases of Handling DISCARD:
> +	 *  - max_discard_segments == 1
> +	 *    The bios need to be contiguous.
> +	 *  - max_discard_segments > 1
> +	 *    Only nvme right now. It takes every bio as a
> +	 *    range and send them to controller together. The ranges
> +	 *    needn't to be contiguous.

The formatting looks odd.  Also I don't think we should mention the
users here, as others might grow (virtio is in the pipe, SCSI could
be supported easily if someone did the work).

^ permalink raw reply	[flat|nested] 6+ messages in thread
* Re: [PATCH V2] block: fix the DISCARD request merge
  2018-10-20 14:29 [PATCH V2] block: fix the DISCARD request merge Jianchao Wang
  2018-10-22  9:00 ` Christoph Hellwig
@ 2018-10-22  9:06 ` Ming Lei
  2018-10-22  9:08   ` Christoph Hellwig
  1 sibling, 1 reply; 6+ messages in thread
From: Ming Lei @ 2018-10-22  9:06 UTC (permalink / raw)
  To: Jianchao Wang
  Cc: axboe, martin.petersen, tom.leiming, hch, linux-block, linux-kernel

On Sat, Oct 20, 2018 at 10:29:37PM +0800, Jianchao Wang wrote:
> There are two cases when handle DISCARD merge
>  - max_discard_segments == 1
>    bios need to be contiguous
>  - max_discard_segments > 1
>    Only nvme right now. It takes every bio as a range and different
>    range needn't to be contiguous.
> 
> But now, attempt_merge screws this up. It always consider contiguity
> for DISCARD for the case max_discard_segments > 1 and cannot merge
> contiguous DISCARD for the case max_discard_segments == 1, because
> rq_attempt_discard_merge always returns false in this case.
> This patch fixes both of the two cases above.
> 
> Signed-off-by: Jianchao Wang <jianchao.w.wang@oracle.com>
> ---
> 
> V2:
>   - Add max_discard_segments > 1 checking in attempt_merge
>   - Change patch title and comment
>   - Add more comment in attempt_merge
> 
>  block/blk-merge.c | 24 +++++++++++++++++++-----
>  1 file changed, 19 insertions(+), 5 deletions(-)
> 
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index 42a4674..8f22374 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -734,8 +734,15 @@ static struct request *attempt_merge(struct request_queue *q,
>  	/*
>  	 * not contiguous
>  	 */
> -	if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
> -		return NULL;
> +	if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next)) {
> +		/*
> +		 * When max_discard_segments is bigger than 1 (only nvme right
> +		 * now), needn't consider the contiguity.
> +		 */
> +		if (!(req_op(req) == REQ_OP_DISCARD &&
> +		      queue_max_discard_segments(q) > 1))
> +			return NULL;
> +	}
>  
>  	if (rq_data_dir(req) != rq_data_dir(next)
>  	    || req->rq_disk != next->rq_disk
> @@ -757,10 +764,17 @@ static struct request *attempt_merge(struct request_queue *q,
>  	 * If we are allowed to merge, then append bio list
>  	 * from next to rq and release next. merge_requests_fn
>  	 * will have updated segment counts, update sector
> -	 * counts here. Handle DISCARDs separately, as they
> -	 * have separate settings.
> +	 * counts here.
> +	 * Two cases of Handling DISCARD:
> +	 *  - max_discard_segments == 1
> +	 *    The bios need to be contiguous.
> +	 *  - max_discard_segments > 1
> +	 *    Only nvme right now. It takes every bio as a
> +	 *    range and send them to controller together. The ranges
> +	 *    needn't to be contiguous.
>  	 */
> -	if (req_op(req) == REQ_OP_DISCARD) {
> +	if (req_op(req) == REQ_OP_DISCARD &&
> +	    queue_max_discard_segments(q) > 1) {
>  		if (!req_attempt_discard_merge(q, req, next))
>  			return NULL;

Looks fine,

Reviewed-by: Ming Lei <ming.lei@redhat.com>

The above may be changed to 'if (blk_try_merge(req) == ELEVATOR_DISCARD_MERGE)'
or sort of in future, which may has document benefit at least, since
ELEVATOR_DISCARD_MERGE means multi-segment discard merge.


Thanks,
Ming

^ permalink raw reply	[flat|nested] 6+ messages in thread
* Re: [PATCH V2] block: fix the DISCARD request merge
  2018-10-22  9:06 ` Ming Lei
@ 2018-10-22  9:08   ` Christoph Hellwig
  2018-10-22 10:14     ` jianchao.wang
  0 siblings, 1 reply; 6+ messages in thread
From: Christoph Hellwig @ 2018-10-22  9:08 UTC (permalink / raw)
  To: Ming Lei
  Cc: Jianchao Wang, axboe, martin.petersen, tom.leiming, hch,
	linux-block, linux-kernel

On Mon, Oct 22, 2018 at 05:06:02PM +0800, Ming Lei wrote:
> 
> The above may be changed to 'if (blk_try_merge(req) == ELEVATOR_DISCARD_MERGE)'
> or sort of in future, which may has document benefit at least, since
> ELEVATOR_DISCARD_MERGE means multi-segment discard merge.

I like that idea, and we should do it for the respin

^ permalink raw reply	[flat|nested] 6+ messages in thread
* Re: [PATCH V2] block: fix the DISCARD request merge
  2018-10-22  9:00 ` Christoph Hellwig
@ 2018-10-22 10:13   ` jianchao.wang
  0 siblings, 0 replies; 6+ messages in thread
From: jianchao.wang @ 2018-10-22 10:13 UTC (permalink / raw)
  To: Christoph Hellwig
  Cc: axboe, martin.petersen, tom.leiming, linux-block, linux-kernel



On 10/22/18 5:00 PM, Christoph Hellwig wrote:
> On Sat, Oct 20, 2018 at 10:29:37PM +0800, Jianchao Wang wrote:
>> There are two cases when handle DISCARD merge
>>  - max_discard_segments == 1
>>    bios need to be contiguous
>>  - max_discard_segments > 1
>>    Only nvme right now. It takes every bio as a range and different
>>    range needn't to be contiguous.
>>
>> But now, attempt_merge screws this up. It always consider contiguity
>> for DISCARD for the case max_discard_segments > 1 and cannot merge
>> contiguous DISCARD for the case max_discard_segments == 1, because
>> rq_attempt_discard_merge always returns false in this case.
>> This patch fixes both of the two cases above.
>>
>> Signed-off-by: Jianchao Wang <jianchao.w.wang@oracle.com>
>> ---
>>
>> V2:
>>   - Add max_discard_segments > 1 checking in attempt_merge
>>   - Change patch title and comment
>>   - Add more comment in attempt_merge
>>
>>  block/blk-merge.c | 24 +++++++++++++++++++-----
>>  1 file changed, 19 insertions(+), 5 deletions(-)
>>
>> diff --git a/block/blk-merge.c b/block/blk-merge.c
>> index 42a4674..8f22374 100644
>> --- a/block/blk-merge.c
>> +++ b/block/blk-merge.c
>> @@ -734,8 +734,15 @@ static struct request *attempt_merge(struct request_queue *q,
>>  	/*
>>  	 * not contiguous
>>  	 */
>> -	if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
>> -		return NULL;
>> +	if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next)) {
>> +		/*
>> +		 * When max_discard_segments is bigger than 1 (only nvme right
>> +		 * now), needn't consider the contiguity.
>> +		 */
>> +		if (!(req_op(req) == REQ_OP_DISCARD &&
>> +		      queue_max_discard_segments(q) > 1))
>> +			return NULL;
> 
> Why not:
> 
> 		if (req_op(req) != REQ_OP_DISCARD ||
> 		    queue_max_discard_segments(q) == 1)> 
> which would be a lot more obvious?

OK, I will change it

> 
>> +	 * counts here.
>> +	 * Two cases of Handling DISCARD:
>> +	 *  - max_discard_segments == 1
>> +	 *    The bios need to be contiguous.
>> +	 *  - max_discard_segments > 1
>> +	 *    Only nvme right now. It takes every bio as a
>> +	 *    range and send them to controller together. The ranges
>> +	 *    needn't to be contiguous.
> 
> The formatting looks odd.  Also I don't think we should mention the
> users here, as others might grow (virtio is in the pipe, SCSI could
> be supported easily if someone did the work).
> 

Yes, I will change the format and discard the users here.

Thanks
Jianchao

^ permalink raw reply	[flat|nested] 6+ messages in thread
* Re: [PATCH V2] block: fix the DISCARD request merge
  2018-10-22  9:08   ` Christoph Hellwig
@ 2018-10-22 10:14     ` jianchao.wang
  0 siblings, 0 replies; 6+ messages in thread
From: jianchao.wang @ 2018-10-22 10:14 UTC (permalink / raw)
  To: Christoph Hellwig, Ming Lei
  Cc: axboe, martin.petersen, tom.leiming, linux-block, linux-kernel



On 10/22/18 5:08 PM, Christoph Hellwig wrote:
> On Mon, Oct 22, 2018 at 05:06:02PM +0800, Ming Lei wrote:
>>
>> The above may be changed to 'if (blk_try_merge(req) == ELEVATOR_DISCARD_MERGE)'
>> or sort of in future, which may has document benefit at least, since
>> ELEVATOR_DISCARD_MERGE means multi-segment discard merge.
> 
> I like that idea, and we should do it for the respin
> 

OK, I will use the blk_try_merge in next version.

Thanks
Jianchao

^ permalink raw reply	[flat|nested] 6+ messages in thread
end of thread, other threads:[~2018-10-22 10:14 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
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2018-10-20 14:29 [PATCH V2] block: fix the DISCARD request merge Jianchao Wang
2018-10-22  9:00 ` Christoph Hellwig
2018-10-22 10:13   ` jianchao.wang
2018-10-22  9:06 ` Ming Lei
2018-10-22  9:08   ` Christoph Hellwig
2018-10-22 10:14     ` jianchao.wang

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