On 10/26/18 4:07 PM, Christoph Hellwig wrote:
> On Fri, Oct 26, 2018 at 04:05:00PM +0800, jianchao.wang wrote:
>> Would anyone please take a look at this ?
>
> I did take a look and reply to it..
Oh sorry, I missed it in my email client.
Got it from the https://lkml.org/lkml/2018/10/24/491
And we could also have a blk_merge_req_ok there. :)
Thanks
Jianchao
>
>>
>> Thanks in advance.
>> Jianchao
>>
>> On 10/24/18 11:07 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.
>>>
>>> Signed-off-by: Jianchao Wang <jianchao.w.w...@oracle.com>
>>> ---
>>>
>>> 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 | 34 ++++++++++++++++++++++++----------
>>> 1 file changed, 24 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/block/blk-merge.c b/block/blk-merge.c
>>> index 42a4674..b258de0 100644
>>> --- a/block/blk-merge.c
>>> +++ b/block/blk-merge.c
>>> @@ -714,6 +714,22 @@ 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;
>>> +}
>>>
>>> /*
>>> * For non-mq, this has to be called with the request spinlock acquired.
>>> @@ -731,12 +747,6 @@ 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 +770,16 @@ 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) {
>>> +
>>> + if (blk_discard_mergable(req)) {
>>> if (!req_attempt_discard_merge(q, req, next))
>>> return NULL;
>>> - } else if (!ll_merge_requests_fn(q, req, next))
>>> + } else if (blk_rq_pos(req) + blk_rq_sectors(req) == blk_rq_pos(next)) {
>>> + if (!ll_merge_requests_fn(q, req, next))
>>> + return NULL;
>>> + } else {
>>> return NULL;
>>> + }
>>>
>>> /*
>>> * If failfast settings disagree or any of the two is already
>>> @@ -888,8 +903,7 @@ 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;
>>>
> ---end quoted text---
>
