]>
git.proxmox.com Git - mirror_ubuntu-eoan-kernel.git/blob - block/blk-merge.c
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 struct bio
*blk_bio_segment_split(struct request_queue
*q
,
169 struct bio_vec bv
, bvprv
, *bvprvp
= NULL
;
170 struct bvec_iter iter
;
171 unsigned seg_size
= 0, nsegs
= 0, sectors
= 0;
172 unsigned front_seg_size
= bio
->bi_seg_front_size
;
173 bool do_split
= true;
174 struct bio
*new = NULL
;
175 const unsigned max_sectors
= get_max_io_size(q
, bio
);
177 bio_for_each_segment(bv
, bio
, iter
) {
179 * If the queue doesn't support SG gaps and adding this
180 * offset would create a gap, disallow it.
182 if (bvprvp
&& bvec_gap_to_prev(q
, bvprvp
, bv
.bv_offset
))
185 if (sectors
+ (bv
.bv_len
>> 9) > max_sectors
) {
187 * Consider this a new segment if we're splitting in
188 * the middle of this vector.
190 if (nsegs
< queue_max_segments(q
) &&
191 sectors
< max_sectors
) {
193 sectors
= max_sectors
;
199 if (seg_size
+ bv
.bv_len
> queue_max_segment_size(q
))
201 if (!biovec_phys_mergeable(q
, bvprvp
, &bv
))
204 seg_size
+= bv
.bv_len
;
207 sectors
+= bv
.bv_len
>> 9;
212 if (nsegs
== queue_max_segments(q
))
215 if (nsegs
== 1 && seg_size
> front_seg_size
)
216 front_seg_size
= seg_size
;
221 seg_size
= bv
.bv_len
;
222 sectors
+= bv
.bv_len
>> 9;
231 new = bio_split(bio
, sectors
, GFP_NOIO
, bs
);
236 if (nsegs
== 1 && seg_size
> front_seg_size
)
237 front_seg_size
= seg_size
;
238 bio
->bi_seg_front_size
= front_seg_size
;
239 if (seg_size
> bio
->bi_seg_back_size
)
240 bio
->bi_seg_back_size
= seg_size
;
242 return do_split
? new : NULL
;
245 void blk_queue_split(struct request_queue
*q
, struct bio
**bio
)
247 struct bio
*split
, *res
;
250 switch (bio_op(*bio
)) {
252 case REQ_OP_SECURE_ERASE
:
253 split
= blk_bio_discard_split(q
, *bio
, &q
->bio_split
, &nsegs
);
255 case REQ_OP_WRITE_ZEROES
:
256 split
= blk_bio_write_zeroes_split(q
, *bio
, &q
->bio_split
, &nsegs
);
258 case REQ_OP_WRITE_SAME
:
259 split
= blk_bio_write_same_split(q
, *bio
, &q
->bio_split
, &nsegs
);
262 split
= blk_bio_segment_split(q
, *bio
, &q
->bio_split
, &nsegs
);
266 /* physical segments can be figured out during splitting */
267 res
= split
? split
: *bio
;
268 res
->bi_phys_segments
= nsegs
;
269 bio_set_flag(res
, BIO_SEG_VALID
);
272 /* there isn't chance to merge the splitted bio */
273 split
->bi_opf
|= REQ_NOMERGE
;
275 bio_chain(split
, *bio
);
276 trace_block_split(q
, split
, (*bio
)->bi_iter
.bi_sector
);
277 generic_make_request(*bio
);
281 EXPORT_SYMBOL(blk_queue_split
);
283 static unsigned int __blk_recalc_rq_segments(struct request_queue
*q
,
287 struct bio_vec bv
, bvprv
= { NULL
};
289 unsigned int seg_size
, nr_phys_segs
;
290 struct bio
*fbio
, *bbio
;
291 struct bvec_iter iter
;
296 switch (bio_op(bio
)) {
298 case REQ_OP_SECURE_ERASE
:
299 case REQ_OP_WRITE_ZEROES
:
301 case REQ_OP_WRITE_SAME
:
309 bio_for_each_segment(bv
, bio
, iter
) {
311 * If SG merging is disabled, each bio vector is
318 if (seg_size
+ bv
.bv_len
319 > queue_max_segment_size(q
))
321 if (!biovec_phys_mergeable(q
, &bvprv
, &bv
))
324 seg_size
+= bv
.bv_len
;
329 if (nr_phys_segs
== 1 && seg_size
>
330 fbio
->bi_seg_front_size
)
331 fbio
->bi_seg_front_size
= seg_size
;
336 seg_size
= bv
.bv_len
;
341 if (nr_phys_segs
== 1 && seg_size
> fbio
->bi_seg_front_size
)
342 fbio
->bi_seg_front_size
= seg_size
;
343 if (seg_size
> bbio
->bi_seg_back_size
)
344 bbio
->bi_seg_back_size
= seg_size
;
349 void blk_recalc_rq_segments(struct request
*rq
)
351 bool no_sg_merge
= !!test_bit(QUEUE_FLAG_NO_SG_MERGE
,
352 &rq
->q
->queue_flags
);
354 rq
->nr_phys_segments
= __blk_recalc_rq_segments(rq
->q
, rq
->bio
,
358 void blk_recount_segments(struct request_queue
*q
, struct bio
*bio
)
360 unsigned short seg_cnt
;
362 /* estimate segment number by bi_vcnt for non-cloned bio */
363 if (bio_flagged(bio
, BIO_CLONED
))
364 seg_cnt
= bio_segments(bio
);
366 seg_cnt
= bio
->bi_vcnt
;
368 if (test_bit(QUEUE_FLAG_NO_SG_MERGE
, &q
->queue_flags
) &&
369 (seg_cnt
< queue_max_segments(q
)))
370 bio
->bi_phys_segments
= seg_cnt
;
372 struct bio
*nxt
= bio
->bi_next
;
375 bio
->bi_phys_segments
= __blk_recalc_rq_segments(q
, bio
, false);
379 bio_set_flag(bio
, BIO_SEG_VALID
);
382 static int blk_phys_contig_segment(struct request_queue
*q
, struct bio
*bio
,
385 struct bio_vec end_bv
= { NULL
}, nxt_bv
;
387 if (bio
->bi_seg_back_size
+ nxt
->bi_seg_front_size
>
388 queue_max_segment_size(q
))
391 if (!bio_has_data(bio
))
394 bio_get_last_bvec(bio
, &end_bv
);
395 bio_get_first_bvec(nxt
, &nxt_bv
);
397 return biovec_phys_mergeable(q
, &end_bv
, &nxt_bv
);
401 __blk_segment_map_sg(struct request_queue
*q
, struct bio_vec
*bvec
,
402 struct scatterlist
*sglist
, struct bio_vec
*bvprv
,
403 struct scatterlist
**sg
, int *nsegs
)
406 int nbytes
= bvec
->bv_len
;
409 if ((*sg
)->length
+ nbytes
> queue_max_segment_size(q
))
411 if (!biovec_phys_mergeable(q
, bvprv
, bvec
))
414 (*sg
)->length
+= nbytes
;
421 * If the driver previously mapped a shorter
422 * list, we could see a termination bit
423 * prematurely unless it fully inits the sg
424 * table on each mapping. We KNOW that there
425 * must be more entries here or the driver
426 * would be buggy, so force clear the
427 * termination bit to avoid doing a full
428 * sg_init_table() in drivers for each command.
434 sg_set_page(*sg
, bvec
->bv_page
, nbytes
, bvec
->bv_offset
);
440 static inline int __blk_bvec_map_sg(struct request_queue
*q
, struct bio_vec bv
,
441 struct scatterlist
*sglist
, struct scatterlist
**sg
)
444 sg_set_page(*sg
, bv
.bv_page
, bv
.bv_len
, bv
.bv_offset
);
448 static int __blk_bios_map_sg(struct request_queue
*q
, struct bio
*bio
,
449 struct scatterlist
*sglist
,
450 struct scatterlist
**sg
)
452 struct bio_vec bvec
, bvprv
= { NULL
};
453 struct bvec_iter iter
;
457 bio_for_each_segment(bvec
, bio
, iter
)
458 __blk_segment_map_sg(q
, &bvec
, sglist
, &bvprv
, sg
,
465 * map a request to scatterlist, return number of sg entries setup. Caller
466 * must make sure sg can hold rq->nr_phys_segments entries
468 int blk_rq_map_sg(struct request_queue
*q
, struct request
*rq
,
469 struct scatterlist
*sglist
)
471 struct scatterlist
*sg
= NULL
;
474 if (rq
->rq_flags
& RQF_SPECIAL_PAYLOAD
)
475 nsegs
= __blk_bvec_map_sg(q
, rq
->special_vec
, sglist
, &sg
);
476 else if (rq
->bio
&& bio_op(rq
->bio
) == REQ_OP_WRITE_SAME
)
477 nsegs
= __blk_bvec_map_sg(q
, bio_iovec(rq
->bio
), sglist
, &sg
);
479 nsegs
= __blk_bios_map_sg(q
, rq
->bio
, sglist
, &sg
);
481 if (unlikely(rq
->rq_flags
& RQF_COPY_USER
) &&
482 (blk_rq_bytes(rq
) & q
->dma_pad_mask
)) {
483 unsigned int pad_len
=
484 (q
->dma_pad_mask
& ~blk_rq_bytes(rq
)) + 1;
486 sg
->length
+= pad_len
;
487 rq
->extra_len
+= pad_len
;
490 if (q
->dma_drain_size
&& q
->dma_drain_needed(rq
)) {
491 if (op_is_write(req_op(rq
)))
492 memset(q
->dma_drain_buffer
, 0, q
->dma_drain_size
);
496 sg_set_page(sg
, virt_to_page(q
->dma_drain_buffer
),
498 ((unsigned long)q
->dma_drain_buffer
) &
501 rq
->extra_len
+= q
->dma_drain_size
;
508 * Something must have been wrong if the figured number of
509 * segment is bigger than number of req's physical segments
511 WARN_ON(nsegs
> blk_rq_nr_phys_segments(rq
));
515 EXPORT_SYMBOL(blk_rq_map_sg
);
517 static inline int ll_new_hw_segment(struct request_queue
*q
,
521 int nr_phys_segs
= bio_phys_segments(q
, bio
);
523 if (req
->nr_phys_segments
+ nr_phys_segs
> queue_max_segments(q
))
526 if (blk_integrity_merge_bio(q
, req
, bio
) == false)
530 * This will form the start of a new hw segment. Bump both
533 req
->nr_phys_segments
+= nr_phys_segs
;
537 req_set_nomerge(q
, req
);
541 int ll_back_merge_fn(struct request_queue
*q
, struct request
*req
,
544 if (req_gap_back_merge(req
, bio
))
546 if (blk_integrity_rq(req
) &&
547 integrity_req_gap_back_merge(req
, bio
))
549 if (blk_rq_sectors(req
) + bio_sectors(bio
) >
550 blk_rq_get_max_sectors(req
, blk_rq_pos(req
))) {
551 req_set_nomerge(q
, req
);
554 if (!bio_flagged(req
->biotail
, BIO_SEG_VALID
))
555 blk_recount_segments(q
, req
->biotail
);
556 if (!bio_flagged(bio
, BIO_SEG_VALID
))
557 blk_recount_segments(q
, bio
);
559 return ll_new_hw_segment(q
, req
, bio
);
562 int ll_front_merge_fn(struct request_queue
*q
, struct request
*req
,
566 if (req_gap_front_merge(req
, bio
))
568 if (blk_integrity_rq(req
) &&
569 integrity_req_gap_front_merge(req
, bio
))
571 if (blk_rq_sectors(req
) + bio_sectors(bio
) >
572 blk_rq_get_max_sectors(req
, bio
->bi_iter
.bi_sector
)) {
573 req_set_nomerge(q
, req
);
576 if (!bio_flagged(bio
, BIO_SEG_VALID
))
577 blk_recount_segments(q
, bio
);
578 if (!bio_flagged(req
->bio
, BIO_SEG_VALID
))
579 blk_recount_segments(q
, req
->bio
);
581 return ll_new_hw_segment(q
, req
, bio
);
584 static bool req_attempt_discard_merge(struct request_queue
*q
, struct request
*req
,
585 struct request
*next
)
587 unsigned short segments
= blk_rq_nr_discard_segments(req
);
589 if (segments
>= queue_max_discard_segments(q
))
591 if (blk_rq_sectors(req
) + bio_sectors(next
->bio
) >
592 blk_rq_get_max_sectors(req
, blk_rq_pos(req
)))
595 req
->nr_phys_segments
= segments
+ blk_rq_nr_discard_segments(next
);
598 req_set_nomerge(q
, req
);
602 static int ll_merge_requests_fn(struct request_queue
*q
, struct request
*req
,
603 struct request
*next
)
605 int total_phys_segments
;
606 unsigned int seg_size
=
607 req
->biotail
->bi_seg_back_size
+ next
->bio
->bi_seg_front_size
;
609 if (req_gap_back_merge(req
, next
->bio
))
613 * Will it become too large?
615 if ((blk_rq_sectors(req
) + blk_rq_sectors(next
)) >
616 blk_rq_get_max_sectors(req
, blk_rq_pos(req
)))
619 total_phys_segments
= req
->nr_phys_segments
+ next
->nr_phys_segments
;
620 if (blk_phys_contig_segment(q
, req
->biotail
, next
->bio
)) {
621 if (req
->nr_phys_segments
== 1)
622 req
->bio
->bi_seg_front_size
= seg_size
;
623 if (next
->nr_phys_segments
== 1)
624 next
->biotail
->bi_seg_back_size
= seg_size
;
625 total_phys_segments
--;
628 if (total_phys_segments
> queue_max_segments(q
))
631 if (blk_integrity_merge_rq(q
, req
, next
) == false)
635 req
->nr_phys_segments
= total_phys_segments
;
640 * blk_rq_set_mixed_merge - mark a request as mixed merge
641 * @rq: request to mark as mixed merge
644 * @rq is about to be mixed merged. Make sure the attributes
645 * which can be mixed are set in each bio and mark @rq as mixed
648 void blk_rq_set_mixed_merge(struct request
*rq
)
650 unsigned int ff
= rq
->cmd_flags
& REQ_FAILFAST_MASK
;
653 if (rq
->rq_flags
& RQF_MIXED_MERGE
)
657 * @rq will no longer represent mixable attributes for all the
658 * contained bios. It will just track those of the first one.
659 * Distributes the attributs to each bio.
661 for (bio
= rq
->bio
; bio
; bio
= bio
->bi_next
) {
662 WARN_ON_ONCE((bio
->bi_opf
& REQ_FAILFAST_MASK
) &&
663 (bio
->bi_opf
& REQ_FAILFAST_MASK
) != ff
);
666 rq
->rq_flags
|= RQF_MIXED_MERGE
;
669 static void blk_account_io_merge(struct request
*req
)
671 if (blk_do_io_stat(req
)) {
672 struct hd_struct
*part
;
677 part_dec_in_flight(req
->q
, part
, rq_data_dir(req
));
684 * Two cases of handling DISCARD merge:
685 * If max_discard_segments > 1, the driver takes every bio
686 * as a range and send them to controller together. The ranges
687 * needn't to be contiguous.
688 * Otherwise, the bios/requests will be handled as same as
689 * others which should be contiguous.
691 static inline bool blk_discard_mergable(struct request
*req
)
693 if (req_op(req
) == REQ_OP_DISCARD
&&
694 queue_max_discard_segments(req
->q
) > 1)
699 static enum elv_merge
blk_try_req_merge(struct request
*req
,
700 struct request
*next
)
702 if (blk_discard_mergable(req
))
703 return ELEVATOR_DISCARD_MERGE
;
704 else if (blk_rq_pos(req
) + blk_rq_sectors(req
) == blk_rq_pos(next
))
705 return ELEVATOR_BACK_MERGE
;
707 return ELEVATOR_NO_MERGE
;
711 * For non-mq, this has to be called with the request spinlock acquired.
712 * For mq with scheduling, the appropriate queue wide lock should be held.
714 static struct request
*attempt_merge(struct request_queue
*q
,
715 struct request
*req
, struct request
*next
)
717 if (!rq_mergeable(req
) || !rq_mergeable(next
))
720 if (req_op(req
) != req_op(next
))
723 if (rq_data_dir(req
) != rq_data_dir(next
)
724 || req
->rq_disk
!= next
->rq_disk
)
727 if (req_op(req
) == REQ_OP_WRITE_SAME
&&
728 !blk_write_same_mergeable(req
->bio
, next
->bio
))
732 * Don't allow merge of different write hints, or for a hint with
735 if (req
->write_hint
!= next
->write_hint
)
738 if (req
->ioprio
!= next
->ioprio
)
742 * If we are allowed to merge, then append bio list
743 * from next to rq and release next. merge_requests_fn
744 * will have updated segment counts, update sector
745 * counts here. Handle DISCARDs separately, as they
746 * have separate settings.
749 switch (blk_try_req_merge(req
, next
)) {
750 case ELEVATOR_DISCARD_MERGE
:
751 if (!req_attempt_discard_merge(q
, req
, next
))
754 case ELEVATOR_BACK_MERGE
:
755 if (!ll_merge_requests_fn(q
, req
, next
))
763 * If failfast settings disagree or any of the two is already
764 * a mixed merge, mark both as mixed before proceeding. This
765 * makes sure that all involved bios have mixable attributes
768 if (((req
->rq_flags
| next
->rq_flags
) & RQF_MIXED_MERGE
) ||
769 (req
->cmd_flags
& REQ_FAILFAST_MASK
) !=
770 (next
->cmd_flags
& REQ_FAILFAST_MASK
)) {
771 blk_rq_set_mixed_merge(req
);
772 blk_rq_set_mixed_merge(next
);
776 * At this point we have either done a back merge or front merge. We
777 * need the smaller start_time_ns of the merged requests to be the
778 * current request for accounting purposes.
780 if (next
->start_time_ns
< req
->start_time_ns
)
781 req
->start_time_ns
= next
->start_time_ns
;
783 req
->biotail
->bi_next
= next
->bio
;
784 req
->biotail
= next
->biotail
;
786 req
->__data_len
+= blk_rq_bytes(next
);
788 if (!blk_discard_mergable(req
))
789 elv_merge_requests(q
, req
, next
);
792 * 'next' is going away, so update stats accordingly
794 blk_account_io_merge(next
);
797 * ownership of bio passed from next to req, return 'next' for
804 struct request
*attempt_back_merge(struct request_queue
*q
, struct request
*rq
)
806 struct request
*next
= elv_latter_request(q
, rq
);
809 return attempt_merge(q
, rq
, next
);
814 struct request
*attempt_front_merge(struct request_queue
*q
, struct request
*rq
)
816 struct request
*prev
= elv_former_request(q
, rq
);
819 return attempt_merge(q
, prev
, rq
);
824 int blk_attempt_req_merge(struct request_queue
*q
, struct request
*rq
,
825 struct request
*next
)
827 struct request
*free
;
829 free
= attempt_merge(q
, rq
, next
);
831 blk_put_request(free
);
838 bool blk_rq_merge_ok(struct request
*rq
, struct bio
*bio
)
840 if (!rq_mergeable(rq
) || !bio_mergeable(bio
))
843 if (req_op(rq
) != bio_op(bio
))
846 /* different data direction or already started, don't merge */
847 if (bio_data_dir(bio
) != rq_data_dir(rq
))
850 /* must be same device */
851 if (rq
->rq_disk
!= bio
->bi_disk
)
854 /* only merge integrity protected bio into ditto rq */
855 if (blk_integrity_merge_bio(rq
->q
, rq
, bio
) == false)
858 /* must be using the same buffer */
859 if (req_op(rq
) == REQ_OP_WRITE_SAME
&&
860 !blk_write_same_mergeable(rq
->bio
, bio
))
864 * Don't allow merge of different write hints, or for a hint with
867 if (rq
->write_hint
!= bio
->bi_write_hint
)
870 if (rq
->ioprio
!= bio_prio(bio
))
876 enum elv_merge
blk_try_merge(struct request
*rq
, struct bio
*bio
)
878 if (blk_discard_mergable(rq
))
879 return ELEVATOR_DISCARD_MERGE
;
880 else if (blk_rq_pos(rq
) + blk_rq_sectors(rq
) == bio
->bi_iter
.bi_sector
)
881 return ELEVATOR_BACK_MERGE
;
882 else if (blk_rq_pos(rq
) - bio_sectors(bio
) == bio
->bi_iter
.bi_sector
)
883 return ELEVATOR_FRONT_MERGE
;
884 return ELEVATOR_NO_MERGE
;