1 // SPDX-License-Identifier: GPL-2.0
3 * Functions related to segment and merge handling
5 #include <linux/kernel.h>
6 #include <linux/module.h>
8 #include <linux/blkdev.h>
9 #include <linux/scatterlist.h>
11 #include <trace/events/block.h>
16 * Check if the two bvecs from two bios can be merged to one segment. If yes,
17 * no need to check gap between the two bios since the 1st bio and the 1st bvec
18 * in the 2nd bio can be handled in one segment.
20 static inline bool bios_segs_mergeable(struct request_queue *q,
21 struct bio *prev, struct bio_vec *prev_last_bv,
22 struct bio_vec *next_first_bv)
24 if (!biovec_phys_mergeable(q, prev_last_bv, next_first_bv))
26 if (prev->bi_seg_back_size + next_first_bv->bv_len >
27 queue_max_segment_size(q))
32 static inline bool bio_will_gap(struct request_queue *q,
33 struct request *prev_rq, struct bio *prev, struct bio *next)
35 struct bio_vec pb, nb;
37 if (!bio_has_data(prev) || !queue_virt_boundary(q))
41 * Don't merge if the 1st bio starts with non-zero offset, otherwise it
42 * is quite difficult to respect the sg gap limit. We work hard to
43 * merge a huge number of small single bios in case of mkfs.
46 bio_get_first_bvec(prev_rq->bio, &pb);
48 bio_get_first_bvec(prev, &pb);
49 if (pb.bv_offset & queue_virt_boundary(q))
53 * We don't need to worry about the situation that the merged segment
54 * ends in unaligned virt boundary:
56 * - if 'pb' ends aligned, the merged segment ends aligned
57 * - if 'pb' ends unaligned, the next bio must include
58 * one single bvec of 'nb', otherwise the 'nb' can't
61 bio_get_last_bvec(prev, &pb);
62 bio_get_first_bvec(next, &nb);
63 if (bios_segs_mergeable(q, prev, &pb, &nb))
65 return __bvec_gap_to_prev(q, &pb, nb.bv_offset);
68 static inline bool req_gap_back_merge(struct request *req, struct bio *bio)
70 return bio_will_gap(req->q, req, req->biotail, bio);
73 static inline bool req_gap_front_merge(struct request *req, struct bio *bio)
75 return bio_will_gap(req->q, NULL, bio, req->bio);
78 static struct bio *blk_bio_discard_split(struct request_queue *q,
83 unsigned int max_discard_sectors, granularity;
86 unsigned split_sectors;
90 /* Zero-sector (unknown) and one-sector granularities are the same. */
91 granularity = max(q->limits.discard_granularity >> 9, 1U);
93 max_discard_sectors = min(q->limits.max_discard_sectors,
94 bio_allowed_max_sectors(q));
95 max_discard_sectors -= max_discard_sectors % granularity;
97 if (unlikely(!max_discard_sectors)) {
102 if (bio_sectors(bio) <= max_discard_sectors)
105 split_sectors = max_discard_sectors;
108 * If the next starting sector would be misaligned, stop the discard at
109 * the previous aligned sector.
111 alignment = (q->limits.discard_alignment >> 9) % granularity;
113 tmp = bio->bi_iter.bi_sector + split_sectors - alignment;
114 tmp = sector_div(tmp, granularity);
116 if (split_sectors > tmp)
117 split_sectors -= tmp;
119 return bio_split(bio, split_sectors, GFP_NOIO, bs);
122 static struct bio *blk_bio_write_zeroes_split(struct request_queue *q,
123 struct bio *bio, struct bio_set *bs, unsigned *nsegs)
127 if (!q->limits.max_write_zeroes_sectors)
130 if (bio_sectors(bio) <= q->limits.max_write_zeroes_sectors)
133 return bio_split(bio, q->limits.max_write_zeroes_sectors, GFP_NOIO, bs);
136 static struct bio *blk_bio_write_same_split(struct request_queue *q,
143 if (!q->limits.max_write_same_sectors)
146 if (bio_sectors(bio) <= q->limits.max_write_same_sectors)
149 return bio_split(bio, q->limits.max_write_same_sectors, GFP_NOIO, bs);
152 static inline unsigned get_max_io_size(struct request_queue *q,
155 unsigned sectors = blk_max_size_offset(q, bio->bi_iter.bi_sector);
156 unsigned mask = queue_logical_block_size(q) - 1;
158 /* aligned to logical block size */
159 sectors &= ~(mask >> 9);
164 static unsigned get_max_segment_size(struct request_queue *q,
167 unsigned long mask = queue_segment_boundary(q);
169 /* default segment boundary mask means no boundary limit */
170 if (mask == BLK_SEG_BOUNDARY_MASK)
171 return queue_max_segment_size(q);
173 return min_t(unsigned long, mask - (mask & offset) + 1,
174 queue_max_segment_size(q));
178 * Split the bvec @bv into segments, and update all kinds of
181 static bool bvec_split_segs(struct request_queue *q, struct bio_vec *bv,
182 unsigned *nsegs, unsigned *last_seg_size,
183 unsigned *front_seg_size, unsigned *sectors)
185 unsigned len = bv->bv_len;
186 unsigned total_len = 0;
187 unsigned new_nsegs = 0, seg_size = 0;
190 * Multi-page bvec may be too big to hold in one segment, so the
191 * current bvec has to be splitted as multiple segments.
193 while (len && new_nsegs + *nsegs < queue_max_segments(q)) {
194 seg_size = get_max_segment_size(q, bv->bv_offset + total_len);
195 seg_size = min(seg_size, len);
198 total_len += seg_size;
201 if ((bv->bv_offset + total_len) & queue_virt_boundary(q))
208 /* update front segment size */
210 unsigned first_seg_size;
213 first_seg_size = get_max_segment_size(q, bv->bv_offset);
215 first_seg_size = queue_max_segment_size(q);
217 if (*front_seg_size < first_seg_size)
218 *front_seg_size = first_seg_size;
221 /* update other varibles */
222 *last_seg_size = seg_size;
225 *sectors += total_len >> 9;
227 /* split in the middle of the bvec if len != 0 */
231 static struct bio *blk_bio_segment_split(struct request_queue *q,
236 struct bio_vec bv, bvprv, *bvprvp = NULL;
237 struct bvec_iter iter;
238 unsigned seg_size = 0, nsegs = 0, sectors = 0;
239 unsigned front_seg_size = bio->bi_seg_front_size;
240 bool do_split = true;
241 struct bio *new = NULL;
242 const unsigned max_sectors = get_max_io_size(q, bio);
244 bio_for_each_bvec(bv, bio, iter) {
246 * If the queue doesn't support SG gaps and adding this
247 * offset would create a gap, disallow it.
249 if (bvprvp && bvec_gap_to_prev(q, bvprvp, bv.bv_offset))
252 if (sectors + (bv.bv_len >> 9) > max_sectors) {
254 * Consider this a new segment if we're splitting in
255 * the middle of this vector.
257 if (nsegs < queue_max_segments(q) &&
258 sectors < max_sectors) {
259 /* split in the middle of bvec */
260 bv.bv_len = (max_sectors - sectors) << 9;
261 bvec_split_segs(q, &bv, &nsegs,
270 if (seg_size + bv.bv_len > queue_max_segment_size(q))
272 if (!biovec_phys_mergeable(q, bvprvp, &bv))
275 seg_size += bv.bv_len;
278 sectors += bv.bv_len >> 9;
280 if (nsegs == 1 && seg_size > front_seg_size)
281 front_seg_size = seg_size;
286 if (nsegs == queue_max_segments(q))
292 if (bv.bv_offset + bv.bv_len <= PAGE_SIZE) {
294 seg_size = bv.bv_len;
295 sectors += bv.bv_len >> 9;
296 if (nsegs == 1 && seg_size > front_seg_size)
297 front_seg_size = seg_size;
298 } else if (bvec_split_segs(q, &bv, &nsegs, &seg_size,
299 &front_seg_size, §ors)) {
309 new = bio_split(bio, sectors, GFP_NOIO, bs);
314 bio->bi_seg_front_size = front_seg_size;
315 if (seg_size > bio->bi_seg_back_size)
316 bio->bi_seg_back_size = seg_size;
318 return do_split ? new : NULL;
321 void blk_queue_split(struct request_queue *q, struct bio **bio)
323 struct bio *split, *res;
326 switch (bio_op(*bio)) {
328 case REQ_OP_SECURE_ERASE:
329 split = blk_bio_discard_split(q, *bio, &q->bio_split, &nsegs);
331 case REQ_OP_WRITE_ZEROES:
332 split = blk_bio_write_zeroes_split(q, *bio, &q->bio_split, &nsegs);
334 case REQ_OP_WRITE_SAME:
335 split = blk_bio_write_same_split(q, *bio, &q->bio_split, &nsegs);
338 split = blk_bio_segment_split(q, *bio, &q->bio_split, &nsegs);
342 /* physical segments can be figured out during splitting */
343 res = split ? split : *bio;
344 res->bi_phys_segments = nsegs;
345 bio_set_flag(res, BIO_SEG_VALID);
348 /* there isn't chance to merge the splitted bio */
349 split->bi_opf |= REQ_NOMERGE;
352 * Since we're recursing into make_request here, ensure
353 * that we mark this bio as already having entered the queue.
354 * If not, and the queue is going away, we can get stuck
355 * forever on waiting for the queue reference to drop. But
356 * that will never happen, as we're already holding a
359 bio_set_flag(*bio, BIO_QUEUE_ENTERED);
361 bio_chain(split, *bio);
362 trace_block_split(q, split, (*bio)->bi_iter.bi_sector);
363 generic_make_request(*bio);
367 EXPORT_SYMBOL(blk_queue_split);
369 static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
372 struct bio_vec bv, bvprv = { NULL };
374 unsigned int seg_size, nr_phys_segs;
375 unsigned front_seg_size;
376 struct bio *fbio, *bbio;
377 struct bvec_iter iter;
382 front_seg_size = bio->bi_seg_front_size;
384 switch (bio_op(bio)) {
386 case REQ_OP_SECURE_ERASE:
387 case REQ_OP_WRITE_ZEROES:
389 case REQ_OP_WRITE_SAME:
397 bio_for_each_bvec(bv, bio, iter) {
399 if (seg_size + bv.bv_len
400 > queue_max_segment_size(q))
402 if (!biovec_phys_mergeable(q, &bvprv, &bv))
405 seg_size += bv.bv_len;
408 if (nr_phys_segs == 1 && seg_size >
410 front_seg_size = seg_size;
417 bvec_split_segs(q, &bv, &nr_phys_segs, &seg_size,
418 &front_seg_size, NULL);
423 fbio->bi_seg_front_size = front_seg_size;
424 if (seg_size > bbio->bi_seg_back_size)
425 bbio->bi_seg_back_size = seg_size;
430 void blk_recalc_rq_segments(struct request *rq)
432 rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio);
435 void blk_recount_segments(struct request_queue *q, struct bio *bio)
437 struct bio *nxt = bio->bi_next;
440 bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio);
443 bio_set_flag(bio, BIO_SEG_VALID);
446 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
449 struct bio_vec end_bv = { NULL }, nxt_bv;
451 if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
452 queue_max_segment_size(q))
455 if (!bio_has_data(bio))
458 bio_get_last_bvec(bio, &end_bv);
459 bio_get_first_bvec(nxt, &nxt_bv);
461 return biovec_phys_mergeable(q, &end_bv, &nxt_bv);
464 static inline struct scatterlist *blk_next_sg(struct scatterlist **sg,
465 struct scatterlist *sglist)
471 * If the driver previously mapped a shorter list, we could see a
472 * termination bit prematurely unless it fully inits the sg table
473 * on each mapping. We KNOW that there must be more entries here
474 * or the driver would be buggy, so force clear the termination bit
475 * to avoid doing a full sg_init_table() in drivers for each command.
481 static unsigned blk_bvec_map_sg(struct request_queue *q,
482 struct bio_vec *bvec, struct scatterlist *sglist,
483 struct scatterlist **sg)
485 unsigned nbytes = bvec->bv_len;
486 unsigned nsegs = 0, total = 0, offset = 0;
493 *sg = blk_next_sg(sg, sglist);
495 seg_size = get_max_segment_size(q, bvec->bv_offset + total);
496 seg_size = min(nbytes, seg_size);
498 offset = (total + bvec->bv_offset) % PAGE_SIZE;
499 idx = (total + bvec->bv_offset) / PAGE_SIZE;
500 pg = bvec_nth_page(bvec->bv_page, idx);
502 sg_set_page(*sg, pg, seg_size, offset);
513 __blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
514 struct scatterlist *sglist, struct bio_vec *bvprv,
515 struct scatterlist **sg, int *nsegs)
518 int nbytes = bvec->bv_len;
521 if ((*sg)->length + nbytes > queue_max_segment_size(q))
523 if (!biovec_phys_mergeable(q, bvprv, bvec))
526 (*sg)->length += nbytes;
529 if (bvec->bv_offset + bvec->bv_len <= PAGE_SIZE) {
530 *sg = blk_next_sg(sg, sglist);
531 sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset);
534 (*nsegs) += blk_bvec_map_sg(q, bvec, sglist, sg);
539 static inline int __blk_bvec_map_sg(struct request_queue *q, struct bio_vec bv,
540 struct scatterlist *sglist, struct scatterlist **sg)
543 sg_set_page(*sg, bv.bv_page, bv.bv_len, bv.bv_offset);
547 static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
548 struct scatterlist *sglist,
549 struct scatterlist **sg)
551 struct bio_vec bvec, bvprv = { NULL };
552 struct bvec_iter iter;
556 bio_for_each_bvec(bvec, bio, iter)
557 __blk_segment_map_sg(q, &bvec, sglist, &bvprv, sg,
564 * map a request to scatterlist, return number of sg entries setup. Caller
565 * must make sure sg can hold rq->nr_phys_segments entries
567 int blk_rq_map_sg(struct request_queue *q, struct request *rq,
568 struct scatterlist *sglist)
570 struct scatterlist *sg = NULL;
573 if (rq->rq_flags & RQF_SPECIAL_PAYLOAD)
574 nsegs = __blk_bvec_map_sg(q, rq->special_vec, sglist, &sg);
575 else if (rq->bio && bio_op(rq->bio) == REQ_OP_WRITE_SAME)
576 nsegs = __blk_bvec_map_sg(q, bio_iovec(rq->bio), sglist, &sg);
578 nsegs = __blk_bios_map_sg(q, rq->bio, sglist, &sg);
580 if (unlikely(rq->rq_flags & RQF_COPY_USER) &&
581 (blk_rq_bytes(rq) & q->dma_pad_mask)) {
582 unsigned int pad_len =
583 (q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1;
585 sg->length += pad_len;
586 rq->extra_len += pad_len;
589 if (q->dma_drain_size && q->dma_drain_needed(rq)) {
590 if (op_is_write(req_op(rq)))
591 memset(q->dma_drain_buffer, 0, q->dma_drain_size);
595 sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
597 ((unsigned long)q->dma_drain_buffer) &
600 rq->extra_len += q->dma_drain_size;
607 * Something must have been wrong if the figured number of
608 * segment is bigger than number of req's physical segments
610 WARN_ON(nsegs > blk_rq_nr_phys_segments(rq));
614 EXPORT_SYMBOL(blk_rq_map_sg);
616 static inline int ll_new_hw_segment(struct request_queue *q,
620 int nr_phys_segs = bio_phys_segments(q, bio);
622 if (req->nr_phys_segments + nr_phys_segs > queue_max_segments(q))
625 if (blk_integrity_merge_bio(q, req, bio) == false)
629 * This will form the start of a new hw segment. Bump both
632 req->nr_phys_segments += nr_phys_segs;
636 req_set_nomerge(q, req);
640 int ll_back_merge_fn(struct request_queue *q, struct request *req,
643 if (req_gap_back_merge(req, bio))
645 if (blk_integrity_rq(req) &&
646 integrity_req_gap_back_merge(req, bio))
648 if (blk_rq_sectors(req) + bio_sectors(bio) >
649 blk_rq_get_max_sectors(req, blk_rq_pos(req))) {
650 req_set_nomerge(q, req);
653 if (!bio_flagged(req->biotail, BIO_SEG_VALID))
654 blk_recount_segments(q, req->biotail);
655 if (!bio_flagged(bio, BIO_SEG_VALID))
656 blk_recount_segments(q, bio);
658 return ll_new_hw_segment(q, req, bio);
661 int ll_front_merge_fn(struct request_queue *q, struct request *req,
665 if (req_gap_front_merge(req, bio))
667 if (blk_integrity_rq(req) &&
668 integrity_req_gap_front_merge(req, bio))
670 if (blk_rq_sectors(req) + bio_sectors(bio) >
671 blk_rq_get_max_sectors(req, bio->bi_iter.bi_sector)) {
672 req_set_nomerge(q, req);
675 if (!bio_flagged(bio, BIO_SEG_VALID))
676 blk_recount_segments(q, bio);
677 if (!bio_flagged(req->bio, BIO_SEG_VALID))
678 blk_recount_segments(q, req->bio);
680 return ll_new_hw_segment(q, req, bio);
683 static bool req_attempt_discard_merge(struct request_queue *q, struct request *req,
684 struct request *next)
686 unsigned short segments = blk_rq_nr_discard_segments(req);
688 if (segments >= queue_max_discard_segments(q))
690 if (blk_rq_sectors(req) + bio_sectors(next->bio) >
691 blk_rq_get_max_sectors(req, blk_rq_pos(req)))
694 req->nr_phys_segments = segments + blk_rq_nr_discard_segments(next);
697 req_set_nomerge(q, req);
701 static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
702 struct request *next)
704 int total_phys_segments;
705 unsigned int seg_size =
706 req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
708 if (req_gap_back_merge(req, next->bio))
712 * Will it become too large?
714 if ((blk_rq_sectors(req) + blk_rq_sectors(next)) >
715 blk_rq_get_max_sectors(req, blk_rq_pos(req)))
718 total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
719 if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
720 if (req->nr_phys_segments == 1)
721 req->bio->bi_seg_front_size = seg_size;
722 if (next->nr_phys_segments == 1)
723 next->biotail->bi_seg_back_size = seg_size;
724 total_phys_segments--;
727 if (total_phys_segments > queue_max_segments(q))
730 if (blk_integrity_merge_rq(q, req, next) == false)
734 req->nr_phys_segments = total_phys_segments;
739 * blk_rq_set_mixed_merge - mark a request as mixed merge
740 * @rq: request to mark as mixed merge
743 * @rq is about to be mixed merged. Make sure the attributes
744 * which can be mixed are set in each bio and mark @rq as mixed
747 void blk_rq_set_mixed_merge(struct request *rq)
749 unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
752 if (rq->rq_flags & RQF_MIXED_MERGE)
756 * @rq will no longer represent mixable attributes for all the
757 * contained bios. It will just track those of the first one.
758 * Distributes the attributs to each bio.
760 for (bio = rq->bio; bio; bio = bio->bi_next) {
761 WARN_ON_ONCE((bio->bi_opf & REQ_FAILFAST_MASK) &&
762 (bio->bi_opf & REQ_FAILFAST_MASK) != ff);
765 rq->rq_flags |= RQF_MIXED_MERGE;
768 static void blk_account_io_merge(struct request *req)
770 if (blk_do_io_stat(req)) {
771 struct hd_struct *part;
776 part_dec_in_flight(req->q, part, rq_data_dir(req));
783 * Two cases of handling DISCARD merge:
784 * If max_discard_segments > 1, the driver takes every bio
785 * as a range and send them to controller together. The ranges
786 * needn't to be contiguous.
787 * Otherwise, the bios/requests will be handled as same as
788 * others which should be contiguous.
790 static inline bool blk_discard_mergable(struct request *req)
792 if (req_op(req) == REQ_OP_DISCARD &&
793 queue_max_discard_segments(req->q) > 1)
798 static enum elv_merge blk_try_req_merge(struct request *req,
799 struct request *next)
801 if (blk_discard_mergable(req))
802 return ELEVATOR_DISCARD_MERGE;
803 else if (blk_rq_pos(req) + blk_rq_sectors(req) == blk_rq_pos(next))
804 return ELEVATOR_BACK_MERGE;
806 return ELEVATOR_NO_MERGE;
810 * For non-mq, this has to be called with the request spinlock acquired.
811 * For mq with scheduling, the appropriate queue wide lock should be held.
813 static struct request *attempt_merge(struct request_queue *q,
814 struct request *req, struct request *next)
816 if (!rq_mergeable(req) || !rq_mergeable(next))
819 if (req_op(req) != req_op(next))
822 if (rq_data_dir(req) != rq_data_dir(next)
823 || req->rq_disk != next->rq_disk)
826 if (req_op(req) == REQ_OP_WRITE_SAME &&
827 !blk_write_same_mergeable(req->bio, next->bio))
831 * Don't allow merge of different write hints, or for a hint with
834 if (req->write_hint != next->write_hint)
837 if (req->ioprio != next->ioprio)
841 * If we are allowed to merge, then append bio list
842 * from next to rq and release next. merge_requests_fn
843 * will have updated segment counts, update sector
844 * counts here. Handle DISCARDs separately, as they
845 * have separate settings.
848 switch (blk_try_req_merge(req, next)) {
849 case ELEVATOR_DISCARD_MERGE:
850 if (!req_attempt_discard_merge(q, req, next))
853 case ELEVATOR_BACK_MERGE:
854 if (!ll_merge_requests_fn(q, req, next))
862 * If failfast settings disagree or any of the two is already
863 * a mixed merge, mark both as mixed before proceeding. This
864 * makes sure that all involved bios have mixable attributes
867 if (((req->rq_flags | next->rq_flags) & RQF_MIXED_MERGE) ||
868 (req->cmd_flags & REQ_FAILFAST_MASK) !=
869 (next->cmd_flags & REQ_FAILFAST_MASK)) {
870 blk_rq_set_mixed_merge(req);
871 blk_rq_set_mixed_merge(next);
875 * At this point we have either done a back merge or front merge. We
876 * need the smaller start_time_ns of the merged requests to be the
877 * current request for accounting purposes.
879 if (next->start_time_ns < req->start_time_ns)
880 req->start_time_ns = next->start_time_ns;
882 req->biotail->bi_next = next->bio;
883 req->biotail = next->biotail;
885 req->__data_len += blk_rq_bytes(next);
887 if (!blk_discard_mergable(req))
888 elv_merge_requests(q, req, next);
891 * 'next' is going away, so update stats accordingly
893 blk_account_io_merge(next);
896 * ownership of bio passed from next to req, return 'next' for
903 struct request *attempt_back_merge(struct request_queue *q, struct request *rq)
905 struct request *next = elv_latter_request(q, rq);
908 return attempt_merge(q, rq, next);
913 struct request *attempt_front_merge(struct request_queue *q, struct request *rq)
915 struct request *prev = elv_former_request(q, rq);
918 return attempt_merge(q, prev, rq);
923 int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
924 struct request *next)
926 struct request *free;
928 free = attempt_merge(q, rq, next);
930 blk_put_request(free);
937 bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
939 if (!rq_mergeable(rq) || !bio_mergeable(bio))
942 if (req_op(rq) != bio_op(bio))
945 /* different data direction or already started, don't merge */
946 if (bio_data_dir(bio) != rq_data_dir(rq))
949 /* must be same device */
950 if (rq->rq_disk != bio->bi_disk)
953 /* only merge integrity protected bio into ditto rq */
954 if (blk_integrity_merge_bio(rq->q, rq, bio) == false)
957 /* must be using the same buffer */
958 if (req_op(rq) == REQ_OP_WRITE_SAME &&
959 !blk_write_same_mergeable(rq->bio, bio))
963 * Don't allow merge of different write hints, or for a hint with
966 if (rq->write_hint != bio->bi_write_hint)
969 if (rq->ioprio != bio_prio(bio))
975 enum elv_merge blk_try_merge(struct request *rq, struct bio *bio)
977 if (blk_discard_mergable(rq))
978 return ELEVATOR_DISCARD_MERGE;
979 else if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
980 return ELEVATOR_BACK_MERGE;
981 else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
982 return ELEVATOR_FRONT_MERGE;
983 return ELEVATOR_NO_MERGE;