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>
14 #include "blk-rq-qos.h"
16 static inline bool bio_will_gap(struct request_queue *q,
17 struct request *prev_rq, struct bio *prev, struct bio *next)
19 struct bio_vec pb, nb;
21 if (!bio_has_data(prev) || !queue_virt_boundary(q))
25 * Don't merge if the 1st bio starts with non-zero offset, otherwise it
26 * is quite difficult to respect the sg gap limit. We work hard to
27 * merge a huge number of small single bios in case of mkfs.
30 bio_get_first_bvec(prev_rq->bio, &pb);
32 bio_get_first_bvec(prev, &pb);
33 if (pb.bv_offset & queue_virt_boundary(q))
37 * We don't need to worry about the situation that the merged segment
38 * ends in unaligned virt boundary:
40 * - if 'pb' ends aligned, the merged segment ends aligned
41 * - if 'pb' ends unaligned, the next bio must include
42 * one single bvec of 'nb', otherwise the 'nb' can't
45 bio_get_last_bvec(prev, &pb);
46 bio_get_first_bvec(next, &nb);
47 if (biovec_phys_mergeable(q, &pb, &nb))
49 return __bvec_gap_to_prev(q, &pb, nb.bv_offset);
52 static inline bool req_gap_back_merge(struct request *req, struct bio *bio)
54 return bio_will_gap(req->q, req, req->biotail, bio);
57 static inline bool req_gap_front_merge(struct request *req, struct bio *bio)
59 return bio_will_gap(req->q, NULL, bio, req->bio);
62 static struct bio *blk_bio_discard_split(struct request_queue *q,
67 unsigned int max_discard_sectors, granularity;
70 unsigned split_sectors;
74 /* Zero-sector (unknown) and one-sector granularities are the same. */
75 granularity = max(q->limits.discard_granularity >> 9, 1U);
77 max_discard_sectors = min(q->limits.max_discard_sectors,
78 bio_allowed_max_sectors(q));
79 max_discard_sectors -= max_discard_sectors % granularity;
81 if (unlikely(!max_discard_sectors)) {
86 if (bio_sectors(bio) <= max_discard_sectors)
89 split_sectors = max_discard_sectors;
92 * If the next starting sector would be misaligned, stop the discard at
93 * the previous aligned sector.
95 alignment = (q->limits.discard_alignment >> 9) % granularity;
97 tmp = bio->bi_iter.bi_sector + split_sectors - alignment;
98 tmp = sector_div(tmp, granularity);
100 if (split_sectors > tmp)
101 split_sectors -= tmp;
103 return bio_split(bio, split_sectors, GFP_NOIO, bs);
106 static struct bio *blk_bio_write_zeroes_split(struct request_queue *q,
107 struct bio *bio, struct bio_set *bs, unsigned *nsegs)
111 if (!q->limits.max_write_zeroes_sectors)
114 if (bio_sectors(bio) <= q->limits.max_write_zeroes_sectors)
117 return bio_split(bio, q->limits.max_write_zeroes_sectors, GFP_NOIO, bs);
120 static struct bio *blk_bio_write_same_split(struct request_queue *q,
127 if (!q->limits.max_write_same_sectors)
130 if (bio_sectors(bio) <= q->limits.max_write_same_sectors)
133 return bio_split(bio, q->limits.max_write_same_sectors, GFP_NOIO, bs);
137 * Return the maximum number of sectors from the start of a bio that may be
138 * submitted as a single request to a block device. If enough sectors remain,
139 * align the end to the physical block size. Otherwise align the end to the
140 * logical block size. This approach minimizes the number of non-aligned
141 * requests that are submitted to a block device if the start of a bio is not
142 * aligned to a physical block boundary.
144 static inline unsigned get_max_io_size(struct request_queue *q,
147 unsigned sectors = blk_max_size_offset(q, bio->bi_iter.bi_sector);
148 unsigned max_sectors = sectors;
149 unsigned pbs = queue_physical_block_size(q) >> SECTOR_SHIFT;
150 unsigned lbs = queue_logical_block_size(q) >> SECTOR_SHIFT;
151 unsigned start_offset = bio->bi_iter.bi_sector & (pbs - 1);
153 max_sectors += start_offset;
154 max_sectors &= ~(pbs - 1);
155 if (max_sectors > start_offset)
156 return max_sectors - start_offset;
158 return sectors & ~(lbs - 1);
161 static inline unsigned get_max_segment_size(const struct request_queue *q,
162 struct page *start_page,
163 unsigned long offset)
165 unsigned long mask = queue_segment_boundary(q);
167 offset = mask & (page_to_phys(start_page) + offset);
170 * overflow may be triggered in case of zero page physical address
171 * on 32bit arch, use queue's max segment size when that happens.
173 return min_not_zero(mask - offset + 1,
174 (unsigned long)queue_max_segment_size(q));
178 * bvec_split_segs - verify whether or not a bvec should be split in the middle
179 * @q: [in] request queue associated with the bio associated with @bv
180 * @bv: [in] bvec to examine
181 * @nsegs: [in,out] Number of segments in the bio being built. Incremented
182 * by the number of segments from @bv that may be appended to that
183 * bio without exceeding @max_segs
184 * @sectors: [in,out] Number of sectors in the bio being built. Incremented
185 * by the number of sectors from @bv that may be appended to that
186 * bio without exceeding @max_sectors
187 * @max_segs: [in] upper bound for *@nsegs
188 * @max_sectors: [in] upper bound for *@sectors
190 * When splitting a bio, it can happen that a bvec is encountered that is too
191 * big to fit in a single segment and hence that it has to be split in the
192 * middle. This function verifies whether or not that should happen. The value
193 * %true is returned if and only if appending the entire @bv to a bio with
194 * *@nsegs segments and *@sectors sectors would make that bio unacceptable for
197 static bool bvec_split_segs(const struct request_queue *q,
198 const struct bio_vec *bv, unsigned *nsegs,
199 unsigned *sectors, unsigned max_segs,
200 unsigned max_sectors)
202 unsigned max_len = (min(max_sectors, UINT_MAX >> 9) - *sectors) << 9;
203 unsigned len = min(bv->bv_len, max_len);
204 unsigned total_len = 0;
205 unsigned seg_size = 0;
207 while (len && *nsegs < max_segs) {
208 seg_size = get_max_segment_size(q, bv->bv_page,
209 bv->bv_offset + total_len);
210 seg_size = min(seg_size, len);
213 total_len += seg_size;
216 if ((bv->bv_offset + total_len) & queue_virt_boundary(q))
220 *sectors += total_len >> 9;
222 /* tell the caller to split the bvec if it is too big to fit */
223 return len > 0 || bv->bv_len > max_len;
227 * blk_bio_segment_split - split a bio in two bios
228 * @q: [in] request queue pointer
229 * @bio: [in] bio to be split
230 * @bs: [in] bio set to allocate the clone from
231 * @segs: [out] number of segments in the bio with the first half of the sectors
233 * Clone @bio, update the bi_iter of the clone to represent the first sectors
234 * of @bio and update @bio->bi_iter to represent the remaining sectors. The
235 * following is guaranteed for the cloned bio:
236 * - That it has at most get_max_io_size(@q, @bio) sectors.
237 * - That it has at most queue_max_segments(@q) segments.
239 * Except for discard requests the cloned bio will point at the bi_io_vec of
240 * the original bio. It is the responsibility of the caller to ensure that the
241 * original bio is not freed before the cloned bio. The caller is also
242 * responsible for ensuring that @bs is only destroyed after processing of the
243 * split bio has finished.
245 static struct bio *blk_bio_segment_split(struct request_queue *q,
250 struct bio_vec bv, bvprv, *bvprvp = NULL;
251 struct bvec_iter iter;
252 unsigned nsegs = 0, sectors = 0;
253 const unsigned max_sectors = get_max_io_size(q, bio);
254 const unsigned max_segs = queue_max_segments(q);
256 bio_for_each_bvec(bv, bio, iter) {
258 * If the queue doesn't support SG gaps and adding this
259 * offset would create a gap, disallow it.
261 if (bvprvp && bvec_gap_to_prev(q, bvprvp, bv.bv_offset))
264 if (nsegs < max_segs &&
265 sectors + (bv.bv_len >> 9) <= max_sectors &&
266 bv.bv_offset + bv.bv_len <= PAGE_SIZE) {
268 sectors += bv.bv_len >> 9;
269 } else if (bvec_split_segs(q, &bv, &nsegs, §ors, max_segs,
282 return bio_split(bio, sectors, GFP_NOIO, bs);
286 * __blk_queue_split - split a bio and submit the second half
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 @bio->bi_disk->queue->bio_split, it is
294 * the responsibility of the caller to ensure that
295 * @bio->bi_disk->queue->bio_split is only released after processing of the
296 * split bio has finished.
298 void __blk_queue_split(struct bio **bio, unsigned int *nr_segs)
300 struct request_queue *q = (*bio)->bi_disk->queue;
301 struct bio *split = NULL;
303 switch (bio_op(*bio)) {
305 case REQ_OP_SECURE_ERASE:
306 split = blk_bio_discard_split(q, *bio, &q->bio_split, nr_segs);
308 case REQ_OP_WRITE_ZEROES:
309 split = blk_bio_write_zeroes_split(q, *bio, &q->bio_split,
312 case REQ_OP_WRITE_SAME:
313 split = blk_bio_write_same_split(q, *bio, &q->bio_split,
318 * All drivers must accept single-segments bios that are <=
319 * PAGE_SIZE. This is a quick and dirty check that relies on
320 * the fact that bi_io_vec[0] is always valid if a bio has data.
321 * The check might lead to occasional false negatives when bios
322 * are cloned, but compared to the performance impact of cloned
323 * bios themselves the loop below doesn't matter anyway.
325 if (!q->limits.chunk_sectors &&
326 (*bio)->bi_vcnt == 1 &&
327 ((*bio)->bi_io_vec[0].bv_len +
328 (*bio)->bi_io_vec[0].bv_offset) <= PAGE_SIZE) {
332 split = blk_bio_segment_split(q, *bio, &q->bio_split, nr_segs);
337 /* there isn't chance to merge the splitted bio */
338 split->bi_opf |= REQ_NOMERGE;
340 bio_chain(split, *bio);
341 trace_block_split(q, split, (*bio)->bi_iter.bi_sector);
342 submit_bio_noacct(*bio);
348 * blk_queue_split - split a bio and submit the second half
349 * @bio: [in, out] bio to be split
351 * Split a bio into two bios, chains the two bios, submit the second half and
352 * store a pointer to the first half in *@bio. Since this function may allocate
353 * a new bio from @bio->bi_disk->queue->bio_split, it is the responsibility of
354 * the caller to ensure that @bio->bi_disk->queue->bio_split is only released
355 * after processing of the split bio has finished.
357 void blk_queue_split(struct bio **bio)
359 unsigned int nr_segs;
361 __blk_queue_split(bio, &nr_segs);
363 EXPORT_SYMBOL(blk_queue_split);
365 unsigned int blk_recalc_rq_segments(struct request *rq)
367 unsigned int nr_phys_segs = 0;
368 unsigned int nr_sectors = 0;
369 struct req_iterator iter;
375 switch (bio_op(rq->bio)) {
377 case REQ_OP_SECURE_ERASE:
378 case REQ_OP_WRITE_ZEROES:
380 case REQ_OP_WRITE_SAME:
384 rq_for_each_bvec(bv, rq, iter)
385 bvec_split_segs(rq->q, &bv, &nr_phys_segs, &nr_sectors,
390 static inline struct scatterlist *blk_next_sg(struct scatterlist **sg,
391 struct scatterlist *sglist)
397 * If the driver previously mapped a shorter list, we could see a
398 * termination bit prematurely unless it fully inits the sg table
399 * on each mapping. We KNOW that there must be more entries here
400 * or the driver would be buggy, so force clear the termination bit
401 * to avoid doing a full sg_init_table() in drivers for each command.
407 static unsigned blk_bvec_map_sg(struct request_queue *q,
408 struct bio_vec *bvec, struct scatterlist *sglist,
409 struct scatterlist **sg)
411 unsigned nbytes = bvec->bv_len;
412 unsigned nsegs = 0, total = 0;
415 unsigned offset = bvec->bv_offset + total;
416 unsigned len = min(get_max_segment_size(q, bvec->bv_page,
418 struct page *page = bvec->bv_page;
421 * Unfortunately a fair number of drivers barf on scatterlists
422 * that have an offset larger than PAGE_SIZE, despite other
423 * subsystems dealing with that invariant just fine. For now
424 * stick to the legacy format where we never present those from
425 * the block layer, but the code below should be removed once
426 * these offenders (mostly MMC/SD drivers) are fixed.
428 page += (offset >> PAGE_SHIFT);
429 offset &= ~PAGE_MASK;
431 *sg = blk_next_sg(sg, sglist);
432 sg_set_page(*sg, page, len, offset);
442 static inline int __blk_bvec_map_sg(struct bio_vec bv,
443 struct scatterlist *sglist, struct scatterlist **sg)
445 *sg = blk_next_sg(sg, sglist);
446 sg_set_page(*sg, bv.bv_page, bv.bv_len, bv.bv_offset);
450 /* only try to merge bvecs into one sg if they are from two bios */
452 __blk_segment_map_sg_merge(struct request_queue *q, struct bio_vec *bvec,
453 struct bio_vec *bvprv, struct scatterlist **sg)
456 int nbytes = bvec->bv_len;
461 if ((*sg)->length + nbytes > queue_max_segment_size(q))
464 if (!biovec_phys_mergeable(q, bvprv, bvec))
467 (*sg)->length += nbytes;
472 static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
473 struct scatterlist *sglist,
474 struct scatterlist **sg)
476 struct bio_vec bvec, bvprv = { NULL };
477 struct bvec_iter iter;
479 bool new_bio = false;
482 bio_for_each_bvec(bvec, bio, iter) {
484 * Only try to merge bvecs from two bios given we
485 * have done bio internal merge when adding pages
489 __blk_segment_map_sg_merge(q, &bvec, &bvprv, sg))
492 if (bvec.bv_offset + bvec.bv_len <= PAGE_SIZE)
493 nsegs += __blk_bvec_map_sg(bvec, sglist, sg);
495 nsegs += blk_bvec_map_sg(q, &bvec, sglist, sg);
499 if (likely(bio->bi_iter.bi_size)) {
509 * map a request to scatterlist, return number of sg entries setup. Caller
510 * must make sure sg can hold rq->nr_phys_segments entries
512 int __blk_rq_map_sg(struct request_queue *q, struct request *rq,
513 struct scatterlist *sglist, struct scatterlist **last_sg)
517 if (rq->rq_flags & RQF_SPECIAL_PAYLOAD)
518 nsegs = __blk_bvec_map_sg(rq->special_vec, sglist, last_sg);
519 else if (rq->bio && bio_op(rq->bio) == REQ_OP_WRITE_SAME)
520 nsegs = __blk_bvec_map_sg(bio_iovec(rq->bio), sglist, last_sg);
522 nsegs = __blk_bios_map_sg(q, rq->bio, sglist, last_sg);
525 sg_mark_end(*last_sg);
528 * Something must have been wrong if the figured number of
529 * segment is bigger than number of req's physical segments
531 WARN_ON(nsegs > blk_rq_nr_phys_segments(rq));
535 EXPORT_SYMBOL(__blk_rq_map_sg);
537 static inline unsigned int blk_rq_get_max_segments(struct request *rq)
539 if (req_op(rq) == REQ_OP_DISCARD)
540 return queue_max_discard_segments(rq->q);
541 return queue_max_segments(rq->q);
544 static inline int ll_new_hw_segment(struct request *req, struct bio *bio,
545 unsigned int nr_phys_segs)
547 if (req->nr_phys_segments + nr_phys_segs > blk_rq_get_max_segments(req))
550 if (blk_integrity_merge_bio(req->q, req, bio) == false)
554 * This will form the start of a new hw segment. Bump both
557 req->nr_phys_segments += nr_phys_segs;
561 req_set_nomerge(req->q, req);
565 int ll_back_merge_fn(struct request *req, struct bio *bio, unsigned int nr_segs)
567 if (req_gap_back_merge(req, bio))
569 if (blk_integrity_rq(req) &&
570 integrity_req_gap_back_merge(req, bio))
572 if (!bio_crypt_ctx_back_mergeable(req, bio))
574 if (blk_rq_sectors(req) + bio_sectors(bio) >
575 blk_rq_get_max_sectors(req, blk_rq_pos(req))) {
576 req_set_nomerge(req->q, req);
580 return ll_new_hw_segment(req, bio, nr_segs);
583 int ll_front_merge_fn(struct request *req, struct bio *bio, unsigned int nr_segs)
585 if (req_gap_front_merge(req, bio))
587 if (blk_integrity_rq(req) &&
588 integrity_req_gap_front_merge(req, bio))
590 if (!bio_crypt_ctx_front_mergeable(req, bio))
592 if (blk_rq_sectors(req) + bio_sectors(bio) >
593 blk_rq_get_max_sectors(req, bio->bi_iter.bi_sector)) {
594 req_set_nomerge(req->q, req);
598 return ll_new_hw_segment(req, bio, nr_segs);
601 static bool req_attempt_discard_merge(struct request_queue *q, struct request *req,
602 struct request *next)
604 unsigned short segments = blk_rq_nr_discard_segments(req);
606 if (segments >= queue_max_discard_segments(q))
608 if (blk_rq_sectors(req) + bio_sectors(next->bio) >
609 blk_rq_get_max_sectors(req, blk_rq_pos(req)))
612 req->nr_phys_segments = segments + blk_rq_nr_discard_segments(next);
615 req_set_nomerge(q, req);
619 static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
620 struct request *next)
622 int total_phys_segments;
624 if (req_gap_back_merge(req, next->bio))
628 * Will it become too large?
630 if ((blk_rq_sectors(req) + blk_rq_sectors(next)) >
631 blk_rq_get_max_sectors(req, blk_rq_pos(req)))
634 total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
635 if (total_phys_segments > blk_rq_get_max_segments(req))
638 if (blk_integrity_merge_rq(q, req, next) == false)
641 if (!bio_crypt_ctx_merge_rq(req, next))
645 req->nr_phys_segments = total_phys_segments;
650 * blk_rq_set_mixed_merge - mark a request as mixed merge
651 * @rq: request to mark as mixed merge
654 * @rq is about to be mixed merged. Make sure the attributes
655 * which can be mixed are set in each bio and mark @rq as mixed
658 void blk_rq_set_mixed_merge(struct request *rq)
660 unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
663 if (rq->rq_flags & RQF_MIXED_MERGE)
667 * @rq will no longer represent mixable attributes for all the
668 * contained bios. It will just track those of the first one.
669 * Distributes the attributs to each bio.
671 for (bio = rq->bio; bio; bio = bio->bi_next) {
672 WARN_ON_ONCE((bio->bi_opf & REQ_FAILFAST_MASK) &&
673 (bio->bi_opf & REQ_FAILFAST_MASK) != ff);
676 rq->rq_flags |= RQF_MIXED_MERGE;
679 static void blk_account_io_merge_request(struct request *req)
681 if (blk_do_io_stat(req)) {
683 part_stat_inc(req->part, merges[op_stat_group(req_op(req))]);
686 hd_struct_put(req->part);
691 * Two cases of handling DISCARD merge:
692 * If max_discard_segments > 1, the driver takes every bio
693 * as a range and send them to controller together. The ranges
694 * needn't to be contiguous.
695 * Otherwise, the bios/requests will be handled as same as
696 * others which should be contiguous.
698 static inline bool blk_discard_mergable(struct request *req)
700 if (req_op(req) == REQ_OP_DISCARD &&
701 queue_max_discard_segments(req->q) > 1)
706 static enum elv_merge blk_try_req_merge(struct request *req,
707 struct request *next)
709 if (blk_discard_mergable(req))
710 return ELEVATOR_DISCARD_MERGE;
711 else if (blk_rq_pos(req) + blk_rq_sectors(req) == blk_rq_pos(next))
712 return ELEVATOR_BACK_MERGE;
714 return ELEVATOR_NO_MERGE;
718 * For non-mq, this has to be called with the request spinlock acquired.
719 * For mq with scheduling, the appropriate queue wide lock should be held.
721 static struct request *attempt_merge(struct request_queue *q,
722 struct request *req, struct request *next)
724 if (!rq_mergeable(req) || !rq_mergeable(next))
727 if (req_op(req) != req_op(next))
730 if (rq_data_dir(req) != rq_data_dir(next)
731 || req->rq_disk != next->rq_disk)
734 if (req_op(req) == REQ_OP_WRITE_SAME &&
735 !blk_write_same_mergeable(req->bio, next->bio))
739 * Don't allow merge of different write hints, or for a hint with
742 if (req->write_hint != next->write_hint)
745 if (req->ioprio != next->ioprio)
749 * If we are allowed to merge, then append bio list
750 * from next to rq and release next. merge_requests_fn
751 * will have updated segment counts, update sector
752 * counts here. Handle DISCARDs separately, as they
753 * have separate settings.
756 switch (blk_try_req_merge(req, next)) {
757 case ELEVATOR_DISCARD_MERGE:
758 if (!req_attempt_discard_merge(q, req, next))
761 case ELEVATOR_BACK_MERGE:
762 if (!ll_merge_requests_fn(q, req, next))
770 * If failfast settings disagree or any of the two is already
771 * a mixed merge, mark both as mixed before proceeding. This
772 * makes sure that all involved bios have mixable attributes
775 if (((req->rq_flags | next->rq_flags) & RQF_MIXED_MERGE) ||
776 (req->cmd_flags & REQ_FAILFAST_MASK) !=
777 (next->cmd_flags & REQ_FAILFAST_MASK)) {
778 blk_rq_set_mixed_merge(req);
779 blk_rq_set_mixed_merge(next);
783 * At this point we have either done a back merge or front merge. We
784 * need the smaller start_time_ns of the merged requests to be the
785 * current request for accounting purposes.
787 if (next->start_time_ns < req->start_time_ns)
788 req->start_time_ns = next->start_time_ns;
790 req->biotail->bi_next = next->bio;
791 req->biotail = next->biotail;
793 req->__data_len += blk_rq_bytes(next);
795 if (!blk_discard_mergable(req))
796 elv_merge_requests(q, req, next);
799 * 'next' is going away, so update stats accordingly
801 blk_account_io_merge_request(next);
803 trace_block_rq_merge(q, next);
806 * ownership of bio passed from next to req, return 'next' for
813 struct request *attempt_back_merge(struct request_queue *q, struct request *rq)
815 struct request *next = elv_latter_request(q, rq);
818 return attempt_merge(q, rq, next);
823 struct request *attempt_front_merge(struct request_queue *q, struct request *rq)
825 struct request *prev = elv_former_request(q, rq);
828 return attempt_merge(q, prev, rq);
833 int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
834 struct request *next)
836 struct request *free;
838 free = attempt_merge(q, rq, next);
840 blk_put_request(free);
847 bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
849 if (!rq_mergeable(rq) || !bio_mergeable(bio))
852 if (req_op(rq) != bio_op(bio))
855 /* different data direction or already started, don't merge */
856 if (bio_data_dir(bio) != rq_data_dir(rq))
859 /* must be same device */
860 if (rq->rq_disk != bio->bi_disk)
863 /* only merge integrity protected bio into ditto rq */
864 if (blk_integrity_merge_bio(rq->q, rq, bio) == false)
867 /* Only merge if the crypt contexts are compatible */
868 if (!bio_crypt_rq_ctx_compatible(rq, bio))
871 /* must be using the same buffer */
872 if (req_op(rq) == REQ_OP_WRITE_SAME &&
873 !blk_write_same_mergeable(rq->bio, bio))
877 * Don't allow merge of different write hints, or for a hint with
880 if (rq->write_hint != bio->bi_write_hint)
883 if (rq->ioprio != bio_prio(bio))
889 enum elv_merge blk_try_merge(struct request *rq, struct bio *bio)
891 if (blk_discard_mergable(rq))
892 return ELEVATOR_DISCARD_MERGE;
893 else if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
894 return ELEVATOR_BACK_MERGE;
895 else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
896 return ELEVATOR_FRONT_MERGE;
897 return ELEVATOR_NO_MERGE;
900 static void blk_account_io_merge_bio(struct request *req)
902 if (!blk_do_io_stat(req))
906 part_stat_inc(req->part, merges[op_stat_group(req_op(req))]);
910 bool bio_attempt_back_merge(struct request *req, struct bio *bio,
911 unsigned int nr_segs)
913 const int ff = bio->bi_opf & REQ_FAILFAST_MASK;
915 if (!ll_back_merge_fn(req, bio, nr_segs))
918 trace_block_bio_backmerge(req->q, req, bio);
919 rq_qos_merge(req->q, req, bio);
921 if ((req->cmd_flags & REQ_FAILFAST_MASK) != ff)
922 blk_rq_set_mixed_merge(req);
924 req->biotail->bi_next = bio;
926 req->__data_len += bio->bi_iter.bi_size;
928 bio_crypt_free_ctx(bio);
930 blk_account_io_merge_bio(req);
934 bool bio_attempt_front_merge(struct request *req, struct bio *bio,
935 unsigned int nr_segs)
937 const int ff = bio->bi_opf & REQ_FAILFAST_MASK;
939 if (!ll_front_merge_fn(req, bio, nr_segs))
942 trace_block_bio_frontmerge(req->q, req, bio);
943 rq_qos_merge(req->q, req, bio);
945 if ((req->cmd_flags & REQ_FAILFAST_MASK) != ff)
946 blk_rq_set_mixed_merge(req);
948 bio->bi_next = req->bio;
951 req->__sector = bio->bi_iter.bi_sector;
952 req->__data_len += bio->bi_iter.bi_size;
954 bio_crypt_do_front_merge(req, bio);
956 blk_account_io_merge_bio(req);
960 bool bio_attempt_discard_merge(struct request_queue *q, struct request *req,
963 unsigned short segments = blk_rq_nr_discard_segments(req);
965 if (segments >= queue_max_discard_segments(q))
967 if (blk_rq_sectors(req) + bio_sectors(bio) >
968 blk_rq_get_max_sectors(req, blk_rq_pos(req)))
971 rq_qos_merge(q, req, bio);
973 req->biotail->bi_next = bio;
975 req->__data_len += bio->bi_iter.bi_size;
976 req->nr_phys_segments = segments + 1;
978 blk_account_io_merge_bio(req);
981 req_set_nomerge(q, req);
986 * blk_attempt_plug_merge - try to merge with %current's plugged list
987 * @q: request_queue new bio is being queued at
988 * @bio: new bio being queued
989 * @nr_segs: number of segments in @bio
990 * @same_queue_rq: pointer to &struct request that gets filled in when
991 * another request associated with @q is found on the plug list
992 * (optional, may be %NULL)
994 * Determine whether @bio being queued on @q can be merged with a request
995 * on %current's plugged list. Returns %true if merge was successful,
998 * Plugging coalesces IOs from the same issuer for the same purpose without
999 * going through @q->queue_lock. As such it's more of an issuing mechanism
1000 * than scheduling, and the request, while may have elvpriv data, is not
1001 * added on the elevator at this point. In addition, we don't have
1002 * reliable access to the elevator outside queue lock. Only check basic
1003 * merging parameters without querying the elevator.
1005 * Caller must ensure !blk_queue_nomerges(q) beforehand.
1007 bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
1008 unsigned int nr_segs, struct request **same_queue_rq)
1010 struct blk_plug *plug;
1012 struct list_head *plug_list;
1014 plug = blk_mq_plug(q, bio);
1018 plug_list = &plug->mq_list;
1020 list_for_each_entry_reverse(rq, plug_list, queuelist) {
1021 bool merged = false;
1023 if (rq->q == q && same_queue_rq) {
1025 * Only blk-mq multiple hardware queues case checks the
1026 * rq in the same queue, there should be only one such
1029 *same_queue_rq = rq;
1032 if (rq->q != q || !blk_rq_merge_ok(rq, bio))
1035 switch (blk_try_merge(rq, bio)) {
1036 case ELEVATOR_BACK_MERGE:
1037 merged = bio_attempt_back_merge(rq, bio, nr_segs);
1039 case ELEVATOR_FRONT_MERGE:
1040 merged = bio_attempt_front_merge(rq, bio, nr_segs);
1042 case ELEVATOR_DISCARD_MERGE:
1043 merged = bio_attempt_discard_merge(q, rq, bio);
1057 * Iterate list of requests and see if we can merge this bio with any
1060 bool blk_bio_list_merge(struct request_queue *q, struct list_head *list,
1061 struct bio *bio, unsigned int nr_segs)
1066 list_for_each_entry_reverse(rq, list, queuelist) {
1067 bool merged = false;
1072 if (!blk_rq_merge_ok(rq, bio))
1075 switch (blk_try_merge(rq, bio)) {
1076 case ELEVATOR_BACK_MERGE:
1077 if (blk_mq_sched_allow_merge(q, rq, bio))
1078 merged = bio_attempt_back_merge(rq, bio,
1081 case ELEVATOR_FRONT_MERGE:
1082 if (blk_mq_sched_allow_merge(q, rq, bio))
1083 merged = bio_attempt_front_merge(rq, bio,
1086 case ELEVATOR_DISCARD_MERGE:
1087 merged = bio_attempt_discard_merge(q, rq, bio);
1098 EXPORT_SYMBOL_GPL(blk_bio_list_merge);