There are two cases when handle DISCARD merge.
If max_discard_segments == 1, the bios/requests need to be contiguous
to merge. If max_discard_segments > 1, 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 <[email protected]>
---
V4:
- introduce blk_try_req_merge as suggestion of Christoph.
V3:
- Introduce blk_discard_mergable into attempt_merge and
blk_try_merge.
- Some comment changes.
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 | 47 +++++++++++++++++++++++++++++++++++++----------
1 file changed, 37 insertions(+), 10 deletions(-)
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 42a4674..cf817c7a 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -714,6 +714,32 @@ static void blk_account_io_merge(struct request *req)
part_stat_unlock();
}
}
+/*
+ * 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;
+ else
+ return false;
+}
+
+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))
+ return ELEVATOR_BACK_MERGE;
+
+ return ELEVATOR_NO_MERGE;
+}
/*
* For non-mq, this has to be called with the request spinlock acquired.
@@ -731,12 +757,6 @@ static struct request *attempt_merge(struct request_queue *q,
if (req_op(req) != req_op(next))
return NULL;
- /*
- * not contiguous
- */
- if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
- return NULL;
-
if (rq_data_dir(req) != rq_data_dir(next)
|| req->rq_disk != next->rq_disk
|| req_no_special_merge(next))
@@ -760,11 +780,19 @@ static struct request *attempt_merge(struct request_queue *q,
* counts here. Handle DISCARDs separately, as they
* have separate settings.
*/
- if (req_op(req) == REQ_OP_DISCARD) {
+
+ switch (blk_try_req_merge(req, next)) {
+ case ELEVATOR_DISCARD_MERGE:
if (!req_attempt_discard_merge(q, req, next))
return NULL;
- } else if (!ll_merge_requests_fn(q, req, next))
+ break;
+ case ELEVATOR_BACK_MERGE:
+ if (!ll_merge_requests_fn(q, req, next))
+ return NULL;
+ break;
+ default:
return NULL;
+ }
/*
* If failfast settings disagree or any of the two is already
@@ -888,8 +916,7 @@ bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
enum elv_merge blk_try_merge(struct request *rq, struct bio *bio)
{
- if (req_op(rq) == REQ_OP_DISCARD &&
- queue_max_discard_segments(rq->q) > 1)
+ if (blk_discard_mergable(rq))
return ELEVATOR_DISCARD_MERGE;
else if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
return ELEVATOR_BACK_MERGE;
--
2.7.4
On 10/26/18 3:28 AM, Jianchao Wang wrote:
> There are two cases when handle DISCARD merge.
> If max_discard_segments == 1, the bios/requests need to be contiguous
> to merge. If max_discard_segments > 1, 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.
Looks good to me, but:
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index 42a4674..cf817c7a 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -714,6 +714,32 @@ static void blk_account_io_merge(struct request *req)
> part_stat_unlock();
> }
> }
> +/*
> + * 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;
> + else
> + return false;
> +}
Please get rid of the redundant else.
--
Jens Axboe
Hi Jens
On 10/26/18 10:25 PM, Jens Axboe wrote:
> On 10/26/18 3:28 AM, Jianchao Wang wrote:
>> There are two cases when handle DISCARD merge.
>> If max_discard_segments == 1, the bios/requests need to be contiguous
>> to merge. If max_discard_segments > 1, 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.
>
> Looks good to me, but:
>
>> diff --git a/block/blk-merge.c b/block/blk-merge.c
>> index 42a4674..cf817c7a 100644
>> --- a/block/blk-merge.c
>> +++ b/block/blk-merge.c
>> @@ -714,6 +714,32 @@ static void blk_account_io_merge(struct request *req)
>> part_stat_unlock();
>> }
>> }
>> +/*
>> + * 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;
>> + else
>> + return false;
>> +}
>
> Please get rid of the redundant else.
>
OK, I will change it and post next version.
Thanks
Jianchao