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>
15 static inline bool bio_will_gap(struct request_queue *q,
16 struct request *prev_rq, struct bio *prev, struct bio *next)
18 struct bio_vec pb, nb;
20 if (!bio_has_data(prev) || !queue_virt_boundary(q))
24 * Don't merge if the 1st bio starts with non-zero offset, otherwise it
25 * is quite difficult to respect the sg gap limit. We work hard to
26 * merge a huge number of small single bios in case of mkfs.
29 bio_get_first_bvec(prev_rq->bio, &pb);
31 bio_get_first_bvec(prev, &pb);
32 if (pb.bv_offset & queue_virt_boundary(q))
36 * We don't need to worry about the situation that the merged segment
37 * ends in unaligned virt boundary:
39 * - if 'pb' ends aligned, the merged segment ends aligned
40 * - if 'pb' ends unaligned, the next bio must include
41 * one single bvec of 'nb', otherwise the 'nb' can't
44 bio_get_last_bvec(prev, &pb);
45 bio_get_first_bvec(next, &nb);
46 if (biovec_phys_mergeable(q, &pb, &nb))
48 return __bvec_gap_to_prev(q, &pb, nb.bv_offset);
51 static inline bool req_gap_back_merge(struct request *req, struct bio *bio)
53 return bio_will_gap(req->q, req, req->biotail, bio);
56 static inline bool req_gap_front_merge(struct request *req, struct bio *bio)
58 return bio_will_gap(req->q, NULL, bio, req->bio);
61 static struct bio *blk_bio_discard_split(struct request_queue *q,
66 unsigned int max_discard_sectors, granularity;
69 unsigned split_sectors;
73 /* Zero-sector (unknown) and one-sector granularities are the same. */
74 granularity = max(q->limits.discard_granularity >> 9, 1U);
76 max_discard_sectors = min(q->limits.max_discard_sectors,
77 bio_allowed_max_sectors(q));
78 max_discard_sectors -= max_discard_sectors % granularity;
80 if (unlikely(!max_discard_sectors)) {
85 if (bio_sectors(bio) <= max_discard_sectors)
88 split_sectors = max_discard_sectors;
91 * If the next starting sector would be misaligned, stop the discard at
92 * the previous aligned sector.
94 alignment = (q->limits.discard_alignment >> 9) % granularity;
96 tmp = bio->bi_iter.bi_sector + split_sectors - alignment;
97 tmp = sector_div(tmp, granularity);
99 if (split_sectors > tmp)
100 split_sectors -= tmp;
102 return bio_split(bio, split_sectors, GFP_NOIO, bs);
105 static struct bio *blk_bio_write_zeroes_split(struct request_queue *q,
106 struct bio *bio, struct bio_set *bs, unsigned *nsegs)
110 if (!q->limits.max_write_zeroes_sectors)
113 if (bio_sectors(bio) <= q->limits.max_write_zeroes_sectors)
116 return bio_split(bio, q->limits.max_write_zeroes_sectors, GFP_NOIO, bs);
119 static struct bio *blk_bio_write_same_split(struct request_queue *q,
126 if (!q->limits.max_write_same_sectors)
129 if (bio_sectors(bio) <= q->limits.max_write_same_sectors)
132 return bio_split(bio, q->limits.max_write_same_sectors, GFP_NOIO, bs);
136 * Return the maximum number of sectors from the start of a bio that may be
137 * submitted as a single request to a block device. If enough sectors remain,
138 * align the end to the physical block size. Otherwise align the end to the
139 * logical block size. This approach minimizes the number of non-aligned
140 * requests that are submitted to a block device if the start of a bio is not
141 * aligned to a physical block boundary.
143 static inline unsigned get_max_io_size(struct request_queue *q,
146 unsigned sectors = blk_max_size_offset(q, bio->bi_iter.bi_sector);
147 unsigned max_sectors = sectors;
148 unsigned pbs = queue_physical_block_size(q) >> SECTOR_SHIFT;
149 unsigned lbs = queue_logical_block_size(q) >> SECTOR_SHIFT;
150 unsigned start_offset = bio->bi_iter.bi_sector & (pbs - 1);
152 max_sectors += start_offset;
153 max_sectors &= ~(pbs - 1);
154 if (max_sectors > start_offset)
155 return max_sectors - start_offset;
157 return sectors & (lbs - 1);
160 static inline unsigned get_max_segment_size(const struct request_queue *q,
161 struct page *start_page,
162 unsigned long offset)
164 unsigned long mask = queue_segment_boundary(q);
166 offset = mask & (page_to_phys(start_page) + offset);
169 * overflow may be triggered in case of zero page physical address
170 * on 32bit arch, use queue's max segment size when that happens.
172 return min_not_zero(mask - offset + 1,
173 (unsigned long)queue_max_segment_size(q));
177 * bvec_split_segs - verify whether or not a bvec should be split in the middle
178 * @q: [in] request queue associated with the bio associated with @bv
179 * @bv: [in] bvec to examine
180 * @nsegs: [in,out] Number of segments in the bio being built. Incremented
181 * by the number of segments from @bv that may be appended to that
182 * bio without exceeding @max_segs
183 * @sectors: [in,out] Number of sectors in the bio being built. Incremented
184 * by the number of sectors from @bv that may be appended to that
185 * bio without exceeding @max_sectors
186 * @max_segs: [in] upper bound for *@nsegs
187 * @max_sectors: [in] upper bound for *@sectors
189 * When splitting a bio, it can happen that a bvec is encountered that is too
190 * big to fit in a single segment and hence that it has to be split in the
191 * middle. This function verifies whether or not that should happen. The value
192 * %true is returned if and only if appending the entire @bv to a bio with
193 * *@nsegs segments and *@sectors sectors would make that bio unacceptable for
196 static bool bvec_split_segs(const struct request_queue *q,
197 const struct bio_vec *bv, unsigned *nsegs,
198 unsigned *sectors, unsigned max_segs,
199 unsigned max_sectors)
201 unsigned max_len = (min(max_sectors, UINT_MAX >> 9) - *sectors) << 9;
202 unsigned len = min(bv->bv_len, max_len);
203 unsigned total_len = 0;
204 unsigned seg_size = 0;
206 while (len && *nsegs < max_segs) {
207 seg_size = get_max_segment_size(q, bv->bv_page,
208 bv->bv_offset + total_len);
209 seg_size = min(seg_size, len);
212 total_len += seg_size;
215 if ((bv->bv_offset + total_len) & queue_virt_boundary(q))
219 *sectors += total_len >> 9;
221 /* tell the caller to split the bvec if it is too big to fit */
222 return len > 0 || bv->bv_len > max_len;
226 * blk_bio_segment_split - split a bio in two bios
227 * @q: [in] request queue pointer
228 * @bio: [in] bio to be split
229 * @bs: [in] bio set to allocate the clone from
230 * @segs: [out] number of segments in the bio with the first half of the sectors
232 * Clone @bio, update the bi_iter of the clone to represent the first sectors
233 * of @bio and update @bio->bi_iter to represent the remaining sectors. The
234 * following is guaranteed for the cloned bio:
235 * - That it has at most get_max_io_size(@q, @bio) sectors.
236 * - That it has at most queue_max_segments(@q) segments.
238 * Except for discard requests the cloned bio will point at the bi_io_vec of
239 * the original bio. It is the responsibility of the caller to ensure that the
240 * original bio is not freed before the cloned bio. The caller is also
241 * responsible for ensuring that @bs is only destroyed after processing of the
242 * split bio has finished.
244 static struct bio *blk_bio_segment_split(struct request_queue *q,
249 struct bio_vec bv, bvprv, *bvprvp = NULL;
250 struct bvec_iter iter;
251 unsigned nsegs = 0, sectors = 0;
252 const unsigned max_sectors = get_max_io_size(q, bio);
253 const unsigned max_segs = queue_max_segments(q);
255 bio_for_each_bvec(bv, bio, iter) {
257 * If the queue doesn't support SG gaps and adding this
258 * offset would create a gap, disallow it.
260 if (bvprvp && bvec_gap_to_prev(q, bvprvp, bv.bv_offset))
263 if (nsegs < max_segs &&
264 sectors + (bv.bv_len >> 9) <= max_sectors &&
265 bv.bv_offset + bv.bv_len <= PAGE_SIZE) {
267 sectors += bv.bv_len >> 9;
268 } else if (bvec_split_segs(q, &bv, &nsegs, §ors, max_segs,
281 return bio_split(bio, sectors, GFP_NOIO, bs);
285 * __blk_queue_split - split a bio and submit the second half
286 * @q: [in] request queue pointer
287 * @bio: [in, out] bio to be split
288 * @nr_segs: [out] number of segments in the first bio
290 * Split a bio into two bios, chain the two bios, submit the second half and
291 * store a pointer to the first half in *@bio. If the second bio is still too
292 * big it will be split by a recursive call to this function. Since this
293 * function may allocate a new bio from @q->bio_split, it is the responsibility
294 * of the caller to ensure that @q is only released after processing of the
295 * split bio has finished.
297 void __blk_queue_split(struct request_queue *q, struct bio **bio,
298 unsigned int *nr_segs)
300 struct bio *split = NULL;
302 switch (bio_op(*bio)) {
304 case REQ_OP_SECURE_ERASE:
305 split = blk_bio_discard_split(q, *bio, &q->bio_split, nr_segs);
307 case REQ_OP_WRITE_ZEROES:
308 split = blk_bio_write_zeroes_split(q, *bio, &q->bio_split,
311 case REQ_OP_WRITE_SAME:
312 split = blk_bio_write_same_split(q, *bio, &q->bio_split,
317 * All drivers must accept single-segments bios that are <=
318 * PAGE_SIZE. This is a quick and dirty check that relies on
319 * the fact that bi_io_vec[0] is always valid if a bio has data.
320 * The check might lead to occasional false negatives when bios
321 * are cloned, but compared to the performance impact of cloned
322 * bios themselves the loop below doesn't matter anyway.
324 if (!q->limits.chunk_sectors &&
325 (*bio)->bi_vcnt == 1 &&
326 ((*bio)->bi_io_vec[0].bv_len +
327 (*bio)->bi_io_vec[0].bv_offset) <= PAGE_SIZE) {
331 split = blk_bio_segment_split(q, *bio, &q->bio_split, nr_segs);
336 /* there isn't chance to merge the splitted bio */
337 split->bi_opf |= REQ_NOMERGE;
340 * Since we're recursing into make_request here, ensure
341 * that we mark this bio as already having entered the queue.
342 * If not, and the queue is going away, we can get stuck
343 * forever on waiting for the queue reference to drop. But
344 * that will never happen, as we're already holding a
347 bio_set_flag(*bio, BIO_QUEUE_ENTERED);
349 bio_chain(split, *bio);
350 trace_block_split(q, split, (*bio)->bi_iter.bi_sector);
351 generic_make_request(*bio);
357 * blk_queue_split - split a bio and submit the second half
358 * @q: [in] request queue pointer
359 * @bio: [in, out] bio to be split
361 * Split a bio into two bios, chains the two bios, submit the second half and
362 * store a pointer to the first half in *@bio. Since this function may allocate
363 * a new bio from @q->bio_split, it is the responsibility of the caller to
364 * ensure that @q is only released after processing of the split bio has
367 void blk_queue_split(struct request_queue *q, struct bio **bio)
369 unsigned int nr_segs;
371 __blk_queue_split(q, bio, &nr_segs);
373 EXPORT_SYMBOL(blk_queue_split);
375 unsigned int blk_recalc_rq_segments(struct request *rq)
377 unsigned int nr_phys_segs = 0;
378 unsigned int nr_sectors = 0;
379 struct req_iterator iter;
385 switch (bio_op(rq->bio)) {
387 case REQ_OP_SECURE_ERASE:
388 case REQ_OP_WRITE_ZEROES:
390 case REQ_OP_WRITE_SAME:
394 rq_for_each_bvec(bv, rq, iter)
395 bvec_split_segs(rq->q, &bv, &nr_phys_segs, &nr_sectors,
400 static inline struct scatterlist *blk_next_sg(struct scatterlist **sg,
401 struct scatterlist *sglist)
407 * If the driver previously mapped a shorter list, we could see a
408 * termination bit prematurely unless it fully inits the sg table
409 * on each mapping. We KNOW that there must be more entries here
410 * or the driver would be buggy, so force clear the termination bit
411 * to avoid doing a full sg_init_table() in drivers for each command.
417 static unsigned blk_bvec_map_sg(struct request_queue *q,
418 struct bio_vec *bvec, struct scatterlist *sglist,
419 struct scatterlist **sg)
421 unsigned nbytes = bvec->bv_len;
422 unsigned nsegs = 0, total = 0;
425 unsigned offset = bvec->bv_offset + total;
426 unsigned len = min(get_max_segment_size(q, bvec->bv_page,
428 struct page *page = bvec->bv_page;
431 * Unfortunately a fair number of drivers barf on scatterlists
432 * that have an offset larger than PAGE_SIZE, despite other
433 * subsystems dealing with that invariant just fine. For now
434 * stick to the legacy format where we never present those from
435 * the block layer, but the code below should be removed once
436 * these offenders (mostly MMC/SD drivers) are fixed.
438 page += (offset >> PAGE_SHIFT);
439 offset &= ~PAGE_MASK;
441 *sg = blk_next_sg(sg, sglist);
442 sg_set_page(*sg, page, len, offset);
452 static inline int __blk_bvec_map_sg(struct bio_vec bv,
453 struct scatterlist *sglist, struct scatterlist **sg)
455 *sg = blk_next_sg(sg, sglist);
456 sg_set_page(*sg, bv.bv_page, bv.bv_len, bv.bv_offset);
460 /* only try to merge bvecs into one sg if they are from two bios */
462 __blk_segment_map_sg_merge(struct request_queue *q, struct bio_vec *bvec,
463 struct bio_vec *bvprv, struct scatterlist **sg)
466 int nbytes = bvec->bv_len;
471 if ((*sg)->length + nbytes > queue_max_segment_size(q))
474 if (!biovec_phys_mergeable(q, bvprv, bvec))
477 (*sg)->length += nbytes;
482 static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
483 struct scatterlist *sglist,
484 struct scatterlist **sg)
486 struct bio_vec uninitialized_var(bvec), bvprv = { NULL };
487 struct bvec_iter iter;
489 bool new_bio = false;
492 bio_for_each_bvec(bvec, bio, iter) {
494 * Only try to merge bvecs from two bios given we
495 * have done bio internal merge when adding pages
499 __blk_segment_map_sg_merge(q, &bvec, &bvprv, sg))
502 if (bvec.bv_offset + bvec.bv_len <= PAGE_SIZE)
503 nsegs += __blk_bvec_map_sg(bvec, sglist, sg);
505 nsegs += blk_bvec_map_sg(q, &bvec, sglist, sg);
509 if (likely(bio->bi_iter.bi_size)) {
519 * map a request to scatterlist, return number of sg entries setup. Caller
520 * must make sure sg can hold rq->nr_phys_segments entries
522 int __blk_rq_map_sg(struct request_queue *q, struct request *rq,
523 struct scatterlist *sglist, struct scatterlist **last_sg)
527 if (rq->rq_flags & RQF_SPECIAL_PAYLOAD)
528 nsegs = __blk_bvec_map_sg(rq->special_vec, sglist, last_sg);
529 else if (rq->bio && bio_op(rq->bio) == REQ_OP_WRITE_SAME)
530 nsegs = __blk_bvec_map_sg(bio_iovec(rq->bio), sglist, last_sg);
532 nsegs = __blk_bios_map_sg(q, rq->bio, sglist, last_sg);
534 if (blk_rq_bytes(rq) && (blk_rq_bytes(rq) & q->dma_pad_mask)) {
535 unsigned int pad_len =
536 (q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1;
538 (*last_sg)->length += pad_len;
539 rq->extra_len += pad_len;
542 if (q->dma_drain_size && q->dma_drain_needed(rq)) {
543 if (op_is_write(req_op(rq)))
544 memset(q->dma_drain_buffer, 0, q->dma_drain_size);
546 sg_unmark_end(*last_sg);
547 *last_sg = sg_next(*last_sg);
548 sg_set_page(*last_sg, virt_to_page(q->dma_drain_buffer),
550 ((unsigned long)q->dma_drain_buffer) &
553 rq->extra_len += q->dma_drain_size;
557 sg_mark_end(*last_sg);
560 * Something must have been wrong if the figured number of
561 * segment is bigger than number of req's physical segments
563 WARN_ON(nsegs > blk_rq_nr_phys_segments(rq));
567 EXPORT_SYMBOL(__blk_rq_map_sg);
569 static inline int ll_new_hw_segment(struct request *req, struct bio *bio,
570 unsigned int nr_phys_segs)
572 if (req->nr_phys_segments + nr_phys_segs > queue_max_segments(req->q))
575 if (blk_integrity_merge_bio(req->q, req, bio) == false)
579 * This will form the start of a new hw segment. Bump both
582 req->nr_phys_segments += nr_phys_segs;
586 req_set_nomerge(req->q, req);
590 int ll_back_merge_fn(struct request *req, struct bio *bio, unsigned int nr_segs)
592 if (req_gap_back_merge(req, bio))
594 if (blk_integrity_rq(req) &&
595 integrity_req_gap_back_merge(req, bio))
597 if (blk_rq_sectors(req) + bio_sectors(bio) >
598 blk_rq_get_max_sectors(req, blk_rq_pos(req))) {
599 req_set_nomerge(req->q, req);
603 return ll_new_hw_segment(req, bio, nr_segs);
606 int ll_front_merge_fn(struct request *req, struct bio *bio, unsigned int nr_segs)
608 if (req_gap_front_merge(req, bio))
610 if (blk_integrity_rq(req) &&
611 integrity_req_gap_front_merge(req, bio))
613 if (blk_rq_sectors(req) + bio_sectors(bio) >
614 blk_rq_get_max_sectors(req, bio->bi_iter.bi_sector)) {
615 req_set_nomerge(req->q, req);
619 return ll_new_hw_segment(req, bio, nr_segs);
622 static bool req_attempt_discard_merge(struct request_queue *q, struct request *req,
623 struct request *next)
625 unsigned short segments = blk_rq_nr_discard_segments(req);
627 if (segments >= queue_max_discard_segments(q))
629 if (blk_rq_sectors(req) + bio_sectors(next->bio) >
630 blk_rq_get_max_sectors(req, blk_rq_pos(req)))
633 req->nr_phys_segments = segments + blk_rq_nr_discard_segments(next);
636 req_set_nomerge(q, req);
640 static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
641 struct request *next)
643 int total_phys_segments;
645 if (req_gap_back_merge(req, next->bio))
649 * Will it become too large?
651 if ((blk_rq_sectors(req) + blk_rq_sectors(next)) >
652 blk_rq_get_max_sectors(req, blk_rq_pos(req)))
655 total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
656 if (total_phys_segments > queue_max_segments(q))
659 if (blk_integrity_merge_rq(q, req, next) == false)
663 req->nr_phys_segments = total_phys_segments;
668 * blk_rq_set_mixed_merge - mark a request as mixed merge
669 * @rq: request to mark as mixed merge
672 * @rq is about to be mixed merged. Make sure the attributes
673 * which can be mixed are set in each bio and mark @rq as mixed
676 void blk_rq_set_mixed_merge(struct request *rq)
678 unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
681 if (rq->rq_flags & RQF_MIXED_MERGE)
685 * @rq will no longer represent mixable attributes for all the
686 * contained bios. It will just track those of the first one.
687 * Distributes the attributs to each bio.
689 for (bio = rq->bio; bio; bio = bio->bi_next) {
690 WARN_ON_ONCE((bio->bi_opf & REQ_FAILFAST_MASK) &&
691 (bio->bi_opf & REQ_FAILFAST_MASK) != ff);
694 rq->rq_flags |= RQF_MIXED_MERGE;
697 static void blk_account_io_merge(struct request *req)
699 if (blk_do_io_stat(req)) {
700 struct hd_struct *part;
705 part_dec_in_flight(req->q, part, rq_data_dir(req));
712 * Two cases of handling DISCARD merge:
713 * If max_discard_segments > 1, the driver takes every bio
714 * as a range and send them to controller together. The ranges
715 * needn't to be contiguous.
716 * Otherwise, the bios/requests will be handled as same as
717 * others which should be contiguous.
719 static inline bool blk_discard_mergable(struct request *req)
721 if (req_op(req) == REQ_OP_DISCARD &&
722 queue_max_discard_segments(req->q) > 1)
727 static enum elv_merge blk_try_req_merge(struct request *req,
728 struct request *next)
730 if (blk_discard_mergable(req))
731 return ELEVATOR_DISCARD_MERGE;
732 else if (blk_rq_pos(req) + blk_rq_sectors(req) == blk_rq_pos(next))
733 return ELEVATOR_BACK_MERGE;
735 return ELEVATOR_NO_MERGE;
739 * For non-mq, this has to be called with the request spinlock acquired.
740 * For mq with scheduling, the appropriate queue wide lock should be held.
742 static struct request *attempt_merge(struct request_queue *q,
743 struct request *req, struct request *next)
745 if (!rq_mergeable(req) || !rq_mergeable(next))
748 if (req_op(req) != req_op(next))
751 if (rq_data_dir(req) != rq_data_dir(next)
752 || req->rq_disk != next->rq_disk)
755 if (req_op(req) == REQ_OP_WRITE_SAME &&
756 !blk_write_same_mergeable(req->bio, next->bio))
760 * Don't allow merge of different write hints, or for a hint with
763 if (req->write_hint != next->write_hint)
766 if (req->ioprio != next->ioprio)
770 * If we are allowed to merge, then append bio list
771 * from next to rq and release next. merge_requests_fn
772 * will have updated segment counts, update sector
773 * counts here. Handle DISCARDs separately, as they
774 * have separate settings.
777 switch (blk_try_req_merge(req, next)) {
778 case ELEVATOR_DISCARD_MERGE:
779 if (!req_attempt_discard_merge(q, req, next))
782 case ELEVATOR_BACK_MERGE:
783 if (!ll_merge_requests_fn(q, req, next))
791 * If failfast settings disagree or any of the two is already
792 * a mixed merge, mark both as mixed before proceeding. This
793 * makes sure that all involved bios have mixable attributes
796 if (((req->rq_flags | next->rq_flags) & RQF_MIXED_MERGE) ||
797 (req->cmd_flags & REQ_FAILFAST_MASK) !=
798 (next->cmd_flags & REQ_FAILFAST_MASK)) {
799 blk_rq_set_mixed_merge(req);
800 blk_rq_set_mixed_merge(next);
804 * At this point we have either done a back merge or front merge. We
805 * need the smaller start_time_ns of the merged requests to be the
806 * current request for accounting purposes.
808 if (next->start_time_ns < req->start_time_ns)
809 req->start_time_ns = next->start_time_ns;
811 req->biotail->bi_next = next->bio;
812 req->biotail = next->biotail;
814 req->__data_len += blk_rq_bytes(next);
816 if (!blk_discard_mergable(req))
817 elv_merge_requests(q, req, next);
820 * 'next' is going away, so update stats accordingly
822 blk_account_io_merge(next);
825 * ownership of bio passed from next to req, return 'next' for
832 struct request *attempt_back_merge(struct request_queue *q, struct request *rq)
834 struct request *next = elv_latter_request(q, rq);
837 return attempt_merge(q, rq, next);
842 struct request *attempt_front_merge(struct request_queue *q, struct request *rq)
844 struct request *prev = elv_former_request(q, rq);
847 return attempt_merge(q, prev, rq);
852 int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
853 struct request *next)
855 struct request *free;
857 free = attempt_merge(q, rq, next);
859 blk_put_request(free);
866 bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
868 if (!rq_mergeable(rq) || !bio_mergeable(bio))
871 if (req_op(rq) != bio_op(bio))
874 /* different data direction or already started, don't merge */
875 if (bio_data_dir(bio) != rq_data_dir(rq))
878 /* must be same device */
879 if (rq->rq_disk != bio->bi_disk)
882 /* only merge integrity protected bio into ditto rq */
883 if (blk_integrity_merge_bio(rq->q, rq, bio) == false)
886 /* must be using the same buffer */
887 if (req_op(rq) == REQ_OP_WRITE_SAME &&
888 !blk_write_same_mergeable(rq->bio, bio))
892 * Don't allow merge of different write hints, or for a hint with
895 if (rq->write_hint != bio->bi_write_hint)
898 if (rq->ioprio != bio_prio(bio))
904 enum elv_merge blk_try_merge(struct request *rq, struct bio *bio)
906 if (blk_discard_mergable(rq))
907 return ELEVATOR_DISCARD_MERGE;
908 else if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
909 return ELEVATOR_BACK_MERGE;
910 else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
911 return ELEVATOR_FRONT_MERGE;
912 return ELEVATOR_NO_MERGE;