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..
>
> 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.wang@xxxxxxxxxx>
> > ---
> >
> > 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---
