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 <[email protected]> > --- > > 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 <[email protected]> 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
