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synced 2024-08-26 10:49:33 +00:00
![Jens Axboe](/assets/img/avatar_default.png)
This reverts commit d380561113
.
If we end up splitting on the first segment, we don't adjust
the sector count. That results in hitting a BUG() with attempting
to split 0 sectors.
As this is just a performance issue and not a regression since
4.3 release, let's just rever this change. That gives us more
time to test a real fix for 4.5, which would be marked for
stable anyway.
760 lines
18 KiB
C
760 lines
18 KiB
C
/*
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* Functions related to segment and merge handling
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*/
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/bio.h>
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#include <linux/blkdev.h>
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#include <linux/scatterlist.h>
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#include "blk.h"
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static struct bio *blk_bio_discard_split(struct request_queue *q,
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struct bio *bio,
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struct bio_set *bs,
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unsigned *nsegs)
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{
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unsigned int max_discard_sectors, granularity;
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int alignment;
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sector_t tmp;
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unsigned split_sectors;
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*nsegs = 1;
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/* Zero-sector (unknown) and one-sector granularities are the same. */
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granularity = max(q->limits.discard_granularity >> 9, 1U);
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max_discard_sectors = min(q->limits.max_discard_sectors, UINT_MAX >> 9);
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max_discard_sectors -= max_discard_sectors % granularity;
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if (unlikely(!max_discard_sectors)) {
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/* XXX: warn */
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return NULL;
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}
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if (bio_sectors(bio) <= max_discard_sectors)
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return NULL;
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split_sectors = max_discard_sectors;
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/*
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* If the next starting sector would be misaligned, stop the discard at
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* the previous aligned sector.
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*/
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alignment = (q->limits.discard_alignment >> 9) % granularity;
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tmp = bio->bi_iter.bi_sector + split_sectors - alignment;
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tmp = sector_div(tmp, granularity);
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if (split_sectors > tmp)
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split_sectors -= tmp;
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return bio_split(bio, split_sectors, GFP_NOIO, bs);
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}
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static struct bio *blk_bio_write_same_split(struct request_queue *q,
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struct bio *bio,
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struct bio_set *bs,
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unsigned *nsegs)
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{
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*nsegs = 1;
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if (!q->limits.max_write_same_sectors)
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return NULL;
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if (bio_sectors(bio) <= q->limits.max_write_same_sectors)
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return NULL;
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return bio_split(bio, q->limits.max_write_same_sectors, GFP_NOIO, bs);
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}
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static struct bio *blk_bio_segment_split(struct request_queue *q,
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struct bio *bio,
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struct bio_set *bs,
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unsigned *segs)
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{
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struct bio_vec bv, bvprv, *bvprvp = NULL;
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struct bvec_iter iter;
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unsigned seg_size = 0, nsegs = 0, sectors = 0;
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unsigned front_seg_size = bio->bi_seg_front_size;
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bool do_split = true;
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struct bio *new = NULL;
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bio_for_each_segment(bv, bio, iter) {
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if (sectors + (bv.bv_len >> 9) > queue_max_sectors(q))
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goto split;
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/*
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* If the queue doesn't support SG gaps and adding this
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* offset would create a gap, disallow it.
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*/
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if (bvprvp && bvec_gap_to_prev(q, bvprvp, bv.bv_offset))
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goto split;
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if (bvprvp && blk_queue_cluster(q)) {
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if (seg_size + bv.bv_len > queue_max_segment_size(q))
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goto new_segment;
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if (!BIOVEC_PHYS_MERGEABLE(bvprvp, &bv))
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goto new_segment;
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if (!BIOVEC_SEG_BOUNDARY(q, bvprvp, &bv))
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goto new_segment;
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seg_size += bv.bv_len;
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bvprv = bv;
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bvprvp = &bvprv;
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sectors += bv.bv_len >> 9;
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if (nsegs == 1 && seg_size > front_seg_size)
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front_seg_size = seg_size;
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continue;
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}
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new_segment:
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if (nsegs == queue_max_segments(q))
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goto split;
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nsegs++;
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bvprv = bv;
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bvprvp = &bvprv;
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seg_size = bv.bv_len;
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sectors += bv.bv_len >> 9;
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if (nsegs == 1 && seg_size > front_seg_size)
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front_seg_size = seg_size;
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}
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do_split = false;
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split:
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*segs = nsegs;
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if (do_split) {
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new = bio_split(bio, sectors, GFP_NOIO, bs);
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if (new)
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bio = new;
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}
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bio->bi_seg_front_size = front_seg_size;
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if (seg_size > bio->bi_seg_back_size)
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bio->bi_seg_back_size = seg_size;
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return do_split ? new : NULL;
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}
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void blk_queue_split(struct request_queue *q, struct bio **bio,
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struct bio_set *bs)
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{
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struct bio *split, *res;
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unsigned nsegs;
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if ((*bio)->bi_rw & REQ_DISCARD)
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split = blk_bio_discard_split(q, *bio, bs, &nsegs);
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else if ((*bio)->bi_rw & REQ_WRITE_SAME)
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split = blk_bio_write_same_split(q, *bio, bs, &nsegs);
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else
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split = blk_bio_segment_split(q, *bio, q->bio_split, &nsegs);
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/* physical segments can be figured out during splitting */
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res = split ? split : *bio;
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res->bi_phys_segments = nsegs;
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bio_set_flag(res, BIO_SEG_VALID);
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if (split) {
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/* there isn't chance to merge the splitted bio */
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split->bi_rw |= REQ_NOMERGE;
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bio_chain(split, *bio);
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generic_make_request(*bio);
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*bio = split;
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}
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}
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EXPORT_SYMBOL(blk_queue_split);
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static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
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struct bio *bio,
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bool no_sg_merge)
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{
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struct bio_vec bv, bvprv = { NULL };
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int cluster, prev = 0;
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unsigned int seg_size, nr_phys_segs;
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struct bio *fbio, *bbio;
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struct bvec_iter iter;
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if (!bio)
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return 0;
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/*
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* This should probably be returning 0, but blk_add_request_payload()
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* (Christoph!!!!)
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*/
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if (bio->bi_rw & REQ_DISCARD)
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return 1;
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if (bio->bi_rw & REQ_WRITE_SAME)
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return 1;
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fbio = bio;
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cluster = blk_queue_cluster(q);
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seg_size = 0;
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nr_phys_segs = 0;
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for_each_bio(bio) {
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bio_for_each_segment(bv, bio, iter) {
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/*
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* If SG merging is disabled, each bio vector is
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* a segment
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*/
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if (no_sg_merge)
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goto new_segment;
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if (prev && cluster) {
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if (seg_size + bv.bv_len
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> queue_max_segment_size(q))
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goto new_segment;
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if (!BIOVEC_PHYS_MERGEABLE(&bvprv, &bv))
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goto new_segment;
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if (!BIOVEC_SEG_BOUNDARY(q, &bvprv, &bv))
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goto new_segment;
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seg_size += bv.bv_len;
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bvprv = bv;
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continue;
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}
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new_segment:
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if (nr_phys_segs == 1 && seg_size >
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fbio->bi_seg_front_size)
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fbio->bi_seg_front_size = seg_size;
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nr_phys_segs++;
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bvprv = bv;
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prev = 1;
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seg_size = bv.bv_len;
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}
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bbio = bio;
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}
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if (nr_phys_segs == 1 && seg_size > fbio->bi_seg_front_size)
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fbio->bi_seg_front_size = seg_size;
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if (seg_size > bbio->bi_seg_back_size)
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bbio->bi_seg_back_size = seg_size;
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return nr_phys_segs;
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}
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void blk_recalc_rq_segments(struct request *rq)
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{
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bool no_sg_merge = !!test_bit(QUEUE_FLAG_NO_SG_MERGE,
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&rq->q->queue_flags);
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rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio,
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no_sg_merge);
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}
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void blk_recount_segments(struct request_queue *q, struct bio *bio)
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{
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unsigned short seg_cnt;
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/* estimate segment number by bi_vcnt for non-cloned bio */
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if (bio_flagged(bio, BIO_CLONED))
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seg_cnt = bio_segments(bio);
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else
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seg_cnt = bio->bi_vcnt;
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if (test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags) &&
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(seg_cnt < queue_max_segments(q)))
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bio->bi_phys_segments = seg_cnt;
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else {
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struct bio *nxt = bio->bi_next;
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bio->bi_next = NULL;
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bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio, false);
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bio->bi_next = nxt;
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}
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bio_set_flag(bio, BIO_SEG_VALID);
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}
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EXPORT_SYMBOL(blk_recount_segments);
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static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
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struct bio *nxt)
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{
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struct bio_vec end_bv = { NULL }, nxt_bv;
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struct bvec_iter iter;
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if (!blk_queue_cluster(q))
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return 0;
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if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
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queue_max_segment_size(q))
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return 0;
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if (!bio_has_data(bio))
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return 1;
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bio_for_each_segment(end_bv, bio, iter)
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if (end_bv.bv_len == iter.bi_size)
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break;
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nxt_bv = bio_iovec(nxt);
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if (!BIOVEC_PHYS_MERGEABLE(&end_bv, &nxt_bv))
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return 0;
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/*
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* bio and nxt are contiguous in memory; check if the queue allows
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* these two to be merged into one
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*/
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if (BIOVEC_SEG_BOUNDARY(q, &end_bv, &nxt_bv))
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return 1;
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return 0;
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}
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static inline void
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__blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
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struct scatterlist *sglist, struct bio_vec *bvprv,
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struct scatterlist **sg, int *nsegs, int *cluster)
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{
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int nbytes = bvec->bv_len;
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if (*sg && *cluster) {
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if ((*sg)->length + nbytes > queue_max_segment_size(q))
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goto new_segment;
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if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
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goto new_segment;
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if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
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goto new_segment;
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(*sg)->length += nbytes;
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} else {
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new_segment:
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if (!*sg)
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*sg = sglist;
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else {
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/*
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* If the driver previously mapped a shorter
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* list, we could see a termination bit
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* prematurely unless it fully inits the sg
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* table on each mapping. We KNOW that there
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* must be more entries here or the driver
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* would be buggy, so force clear the
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* termination bit to avoid doing a full
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* sg_init_table() in drivers for each command.
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*/
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sg_unmark_end(*sg);
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*sg = sg_next(*sg);
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}
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sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset);
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(*nsegs)++;
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}
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*bvprv = *bvec;
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}
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static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
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struct scatterlist *sglist,
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struct scatterlist **sg)
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{
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struct bio_vec bvec, bvprv = { NULL };
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struct bvec_iter iter;
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int nsegs, cluster;
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nsegs = 0;
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cluster = blk_queue_cluster(q);
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if (bio->bi_rw & REQ_DISCARD) {
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/*
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* This is a hack - drivers should be neither modifying the
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* biovec, nor relying on bi_vcnt - but because of
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* blk_add_request_payload(), a discard bio may or may not have
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* a payload we need to set up here (thank you Christoph) and
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* bi_vcnt is really the only way of telling if we need to.
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*/
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if (bio->bi_vcnt)
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goto single_segment;
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return 0;
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}
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if (bio->bi_rw & REQ_WRITE_SAME) {
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single_segment:
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*sg = sglist;
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bvec = bio_iovec(bio);
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sg_set_page(*sg, bvec.bv_page, bvec.bv_len, bvec.bv_offset);
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return 1;
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}
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for_each_bio(bio)
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bio_for_each_segment(bvec, bio, iter)
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__blk_segment_map_sg(q, &bvec, sglist, &bvprv, sg,
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&nsegs, &cluster);
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return nsegs;
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}
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/*
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* map a request to scatterlist, return number of sg entries setup. Caller
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* must make sure sg can hold rq->nr_phys_segments entries
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*/
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int blk_rq_map_sg(struct request_queue *q, struct request *rq,
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struct scatterlist *sglist)
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{
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struct scatterlist *sg = NULL;
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int nsegs = 0;
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if (rq->bio)
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nsegs = __blk_bios_map_sg(q, rq->bio, sglist, &sg);
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if (unlikely(rq->cmd_flags & REQ_COPY_USER) &&
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(blk_rq_bytes(rq) & q->dma_pad_mask)) {
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unsigned int pad_len =
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(q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1;
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sg->length += pad_len;
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rq->extra_len += pad_len;
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}
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if (q->dma_drain_size && q->dma_drain_needed(rq)) {
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if (rq->cmd_flags & REQ_WRITE)
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memset(q->dma_drain_buffer, 0, q->dma_drain_size);
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sg_unmark_end(sg);
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sg = sg_next(sg);
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sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
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q->dma_drain_size,
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((unsigned long)q->dma_drain_buffer) &
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(PAGE_SIZE - 1));
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nsegs++;
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rq->extra_len += q->dma_drain_size;
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}
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if (sg)
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sg_mark_end(sg);
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/*
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* Something must have been wrong if the figured number of
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* segment is bigger than number of req's physical segments
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*/
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WARN_ON(nsegs > rq->nr_phys_segments);
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return nsegs;
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}
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EXPORT_SYMBOL(blk_rq_map_sg);
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static inline int ll_new_hw_segment(struct request_queue *q,
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struct request *req,
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struct bio *bio)
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{
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int nr_phys_segs = bio_phys_segments(q, bio);
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if (req->nr_phys_segments + nr_phys_segs > queue_max_segments(q))
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goto no_merge;
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if (blk_integrity_merge_bio(q, req, bio) == false)
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goto no_merge;
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/*
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* This will form the start of a new hw segment. Bump both
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* counters.
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*/
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req->nr_phys_segments += nr_phys_segs;
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return 1;
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no_merge:
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req->cmd_flags |= REQ_NOMERGE;
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if (req == q->last_merge)
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q->last_merge = NULL;
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return 0;
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}
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int ll_back_merge_fn(struct request_queue *q, struct request *req,
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struct bio *bio)
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{
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if (req_gap_back_merge(req, bio))
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return 0;
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if (blk_integrity_rq(req) &&
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integrity_req_gap_back_merge(req, bio))
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return 0;
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if (blk_rq_sectors(req) + bio_sectors(bio) >
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blk_rq_get_max_sectors(req)) {
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req->cmd_flags |= REQ_NOMERGE;
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if (req == q->last_merge)
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q->last_merge = NULL;
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return 0;
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}
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if (!bio_flagged(req->biotail, BIO_SEG_VALID))
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blk_recount_segments(q, req->biotail);
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if (!bio_flagged(bio, BIO_SEG_VALID))
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blk_recount_segments(q, bio);
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return ll_new_hw_segment(q, req, bio);
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}
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int ll_front_merge_fn(struct request_queue *q, struct request *req,
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struct bio *bio)
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{
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if (req_gap_front_merge(req, bio))
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return 0;
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if (blk_integrity_rq(req) &&
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integrity_req_gap_front_merge(req, bio))
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return 0;
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if (blk_rq_sectors(req) + bio_sectors(bio) >
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blk_rq_get_max_sectors(req)) {
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req->cmd_flags |= REQ_NOMERGE;
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if (req == q->last_merge)
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q->last_merge = NULL;
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return 0;
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}
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if (!bio_flagged(bio, BIO_SEG_VALID))
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blk_recount_segments(q, bio);
|
|
if (!bio_flagged(req->bio, BIO_SEG_VALID))
|
|
blk_recount_segments(q, req->bio);
|
|
|
|
return ll_new_hw_segment(q, req, bio);
|
|
}
|
|
|
|
/*
|
|
* blk-mq uses req->special to carry normal driver per-request payload, it
|
|
* does not indicate a prepared command that we cannot merge with.
|
|
*/
|
|
static bool req_no_special_merge(struct request *req)
|
|
{
|
|
struct request_queue *q = req->q;
|
|
|
|
return !q->mq_ops && req->special;
|
|
}
|
|
|
|
static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
|
|
struct request *next)
|
|
{
|
|
int total_phys_segments;
|
|
unsigned int seg_size =
|
|
req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
|
|
|
|
/*
|
|
* First check if the either of the requests are re-queued
|
|
* requests. Can't merge them if they are.
|
|
*/
|
|
if (req_no_special_merge(req) || req_no_special_merge(next))
|
|
return 0;
|
|
|
|
if (req_gap_back_merge(req, next->bio))
|
|
return 0;
|
|
|
|
/*
|
|
* Will it become too large?
|
|
*/
|
|
if ((blk_rq_sectors(req) + blk_rq_sectors(next)) >
|
|
blk_rq_get_max_sectors(req))
|
|
return 0;
|
|
|
|
total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
|
|
if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
|
|
if (req->nr_phys_segments == 1)
|
|
req->bio->bi_seg_front_size = seg_size;
|
|
if (next->nr_phys_segments == 1)
|
|
next->biotail->bi_seg_back_size = seg_size;
|
|
total_phys_segments--;
|
|
}
|
|
|
|
if (total_phys_segments > queue_max_segments(q))
|
|
return 0;
|
|
|
|
if (blk_integrity_merge_rq(q, req, next) == false)
|
|
return 0;
|
|
|
|
/* Merge is OK... */
|
|
req->nr_phys_segments = total_phys_segments;
|
|
return 1;
|
|
}
|
|
|
|
/**
|
|
* blk_rq_set_mixed_merge - mark a request as mixed merge
|
|
* @rq: request to mark as mixed merge
|
|
*
|
|
* Description:
|
|
* @rq is about to be mixed merged. Make sure the attributes
|
|
* which can be mixed are set in each bio and mark @rq as mixed
|
|
* merged.
|
|
*/
|
|
void blk_rq_set_mixed_merge(struct request *rq)
|
|
{
|
|
unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
|
|
struct bio *bio;
|
|
|
|
if (rq->cmd_flags & REQ_MIXED_MERGE)
|
|
return;
|
|
|
|
/*
|
|
* @rq will no longer represent mixable attributes for all the
|
|
* contained bios. It will just track those of the first one.
|
|
* Distributes the attributs to each bio.
|
|
*/
|
|
for (bio = rq->bio; bio; bio = bio->bi_next) {
|
|
WARN_ON_ONCE((bio->bi_rw & REQ_FAILFAST_MASK) &&
|
|
(bio->bi_rw & REQ_FAILFAST_MASK) != ff);
|
|
bio->bi_rw |= ff;
|
|
}
|
|
rq->cmd_flags |= REQ_MIXED_MERGE;
|
|
}
|
|
|
|
static void blk_account_io_merge(struct request *req)
|
|
{
|
|
if (blk_do_io_stat(req)) {
|
|
struct hd_struct *part;
|
|
int cpu;
|
|
|
|
cpu = part_stat_lock();
|
|
part = req->part;
|
|
|
|
part_round_stats(cpu, part);
|
|
part_dec_in_flight(part, rq_data_dir(req));
|
|
|
|
hd_struct_put(part);
|
|
part_stat_unlock();
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Has to be called with the request spinlock acquired
|
|
*/
|
|
static int attempt_merge(struct request_queue *q, struct request *req,
|
|
struct request *next)
|
|
{
|
|
if (!rq_mergeable(req) || !rq_mergeable(next))
|
|
return 0;
|
|
|
|
if (!blk_check_merge_flags(req->cmd_flags, next->cmd_flags))
|
|
return 0;
|
|
|
|
/*
|
|
* not contiguous
|
|
*/
|
|
if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
|
|
return 0;
|
|
|
|
if (rq_data_dir(req) != rq_data_dir(next)
|
|
|| req->rq_disk != next->rq_disk
|
|
|| req_no_special_merge(next))
|
|
return 0;
|
|
|
|
if (req->cmd_flags & REQ_WRITE_SAME &&
|
|
!blk_write_same_mergeable(req->bio, next->bio))
|
|
return 0;
|
|
|
|
/*
|
|
* If we are allowed to merge, then append bio list
|
|
* from next to rq and release next. merge_requests_fn
|
|
* will have updated segment counts, update sector
|
|
* counts here.
|
|
*/
|
|
if (!ll_merge_requests_fn(q, req, next))
|
|
return 0;
|
|
|
|
/*
|
|
* If failfast settings disagree or any of the two is already
|
|
* a mixed merge, mark both as mixed before proceeding. This
|
|
* makes sure that all involved bios have mixable attributes
|
|
* set properly.
|
|
*/
|
|
if ((req->cmd_flags | next->cmd_flags) & REQ_MIXED_MERGE ||
|
|
(req->cmd_flags & REQ_FAILFAST_MASK) !=
|
|
(next->cmd_flags & REQ_FAILFAST_MASK)) {
|
|
blk_rq_set_mixed_merge(req);
|
|
blk_rq_set_mixed_merge(next);
|
|
}
|
|
|
|
/*
|
|
* At this point we have either done a back merge
|
|
* or front merge. We need the smaller start_time of
|
|
* the merged requests to be the current request
|
|
* for accounting purposes.
|
|
*/
|
|
if (time_after(req->start_time, next->start_time))
|
|
req->start_time = next->start_time;
|
|
|
|
req->biotail->bi_next = next->bio;
|
|
req->biotail = next->biotail;
|
|
|
|
req->__data_len += blk_rq_bytes(next);
|
|
|
|
elv_merge_requests(q, req, next);
|
|
|
|
/*
|
|
* 'next' is going away, so update stats accordingly
|
|
*/
|
|
blk_account_io_merge(next);
|
|
|
|
req->ioprio = ioprio_best(req->ioprio, next->ioprio);
|
|
if (blk_rq_cpu_valid(next))
|
|
req->cpu = next->cpu;
|
|
|
|
/* owner-ship of bio passed from next to req */
|
|
next->bio = NULL;
|
|
__blk_put_request(q, next);
|
|
return 1;
|
|
}
|
|
|
|
int attempt_back_merge(struct request_queue *q, struct request *rq)
|
|
{
|
|
struct request *next = elv_latter_request(q, rq);
|
|
|
|
if (next)
|
|
return attempt_merge(q, rq, next);
|
|
|
|
return 0;
|
|
}
|
|
|
|
int attempt_front_merge(struct request_queue *q, struct request *rq)
|
|
{
|
|
struct request *prev = elv_former_request(q, rq);
|
|
|
|
if (prev)
|
|
return attempt_merge(q, prev, rq);
|
|
|
|
return 0;
|
|
}
|
|
|
|
int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
|
|
struct request *next)
|
|
{
|
|
return attempt_merge(q, rq, next);
|
|
}
|
|
|
|
bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
|
|
{
|
|
if (!rq_mergeable(rq) || !bio_mergeable(bio))
|
|
return false;
|
|
|
|
if (!blk_check_merge_flags(rq->cmd_flags, bio->bi_rw))
|
|
return false;
|
|
|
|
/* different data direction or already started, don't merge */
|
|
if (bio_data_dir(bio) != rq_data_dir(rq))
|
|
return false;
|
|
|
|
/* must be same device and not a special request */
|
|
if (rq->rq_disk != bio->bi_bdev->bd_disk || req_no_special_merge(rq))
|
|
return false;
|
|
|
|
/* only merge integrity protected bio into ditto rq */
|
|
if (blk_integrity_merge_bio(rq->q, rq, bio) == false)
|
|
return false;
|
|
|
|
/* must be using the same buffer */
|
|
if (rq->cmd_flags & REQ_WRITE_SAME &&
|
|
!blk_write_same_mergeable(rq->bio, bio))
|
|
return false;
|
|
|
|
return true;
|
|
}
|
|
|
|
int blk_try_merge(struct request *rq, struct bio *bio)
|
|
{
|
|
if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
|
|
return ELEVATOR_BACK_MERGE;
|
|
else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
|
|
return ELEVATOR_FRONT_MERGE;
|
|
return ELEVATOR_NO_MERGE;
|
|
}
|