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Commit 5e7c4274 authored by Jens Axboe's avatar Jens Axboe
Browse files

block: Check for gaps on front and back merges 



We are checking for gaps to previous bio_vec, which can
only detect back merges gaps. Moreover, at the point where
we check for a gap, we don't know if we will attempt a back
or a front merge. Thus, check for gap to prev in a back merge
attempt and check for a gap to next in a front merge attempt.

Signed-off-by: default avatarJens Axboe <axboe@fb.com>
[sagig: Minor rename change]
Signed-off-by: default avatarSagi Grimberg <sagig@mellanox.com>
parent 5fdb7e1b

block/blk-merge.c

+6 −13
Original line number Diff line number Diff line
@@ -438,6 +438,8 @@ static inline int ll_new_hw_segment(struct request_queue *q, 
int ll_back_merge_fn(struct request_queue *q, struct request *req,

		     struct bio *bio)

{

	if (req_gap_back_merge(req, bio))

		return 0;

	if (blk_rq_sectors(req) + bio_sectors(bio) >

	    blk_rq_get_max_sectors(req)) {

		req->cmd_flags |= REQ_NOMERGE;
@@ -456,6 +458,9 @@ int ll_back_merge_fn(struct request_queue *q, struct request *req, 
int ll_front_merge_fn(struct request_queue *q, struct request *req,

		      struct bio *bio)

{



	if (req_gap_front_merge(req, bio))

		return 0;

	if (blk_rq_sectors(req) + bio_sectors(bio) >

	    blk_rq_get_max_sectors(req)) {

		req->cmd_flags |= REQ_NOMERGE;
@@ -482,14 +487,6 @@ static bool req_no_special_merge(struct request *req) 
	return !q->mq_ops && req->special;

}



static int req_gap_to_prev(struct request *req, struct bio *next)

{

	struct bio *prev = req->biotail;



	return bvec_gap_to_prev(req->q, &prev->bi_io_vec[prev->bi_vcnt - 1],

			next->bi_io_vec[0].bv_offset);

}



static int ll_merge_requests_fn(struct request_queue *q, struct request *req,

				struct request *next)

{
@@ -504,7 +501,7 @@ static int ll_merge_requests_fn(struct request_queue *q, struct request *req, 
	if (req_no_special_merge(req) || req_no_special_merge(next))

		return 0;



	if (req_gap_to_prev(req, next->bio))

	if (req_gap_back_merge(req, next->bio))

		return 0;



	/*
@@ -712,10 +709,6 @@ bool blk_rq_merge_ok(struct request *rq, struct bio *bio) 
	    !blk_write_same_mergeable(rq->bio, bio))

		return false;



	/* Only check gaps if the bio carries data */

	if (bio_has_data(bio) && req_gap_to_prev(rq, bio))

		return false;



	return true;

}

include/linux/blkdev.h

+20 −0
Original line number Diff line number Diff line
@@ -1368,6 +1368,26 @@ static inline bool bvec_gap_to_prev(struct request_queue *q, 
		((bprv->bv_offset + bprv->bv_len) & queue_virt_boundary(q));

}



static inline bool bio_will_gap(struct request_queue *q, struct bio *prev,

			 struct bio *next)

{

	if (!bio_has_data(prev))

		return false;



	return bvec_gap_to_prev(q, &prev->bi_io_vec[prev->bi_vcnt - 1],

				next->bi_io_vec[0].bv_offset);

}



static inline bool req_gap_back_merge(struct request *req, struct bio *bio)

{

	return bio_will_gap(req->q, req->biotail, bio);

}



static inline bool req_gap_front_merge(struct request *req, struct bio *bio)

{

	return bio_will_gap(req->q, bio, req->bio);

}



struct work_struct;

int kblockd_schedule_work(struct work_struct *work);

int kblockd_schedule_delayed_work(struct delayed_work *dwork, unsigned long delay);