Release 4.12 block/blk-merge.c

/*
 * Functions related to segment and merge handling
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/scatterlist.h>

#include <trace/events/block.h>

#include "blk.h"



static struct bio *blk_bio_discard_split(struct request_queue *q,
					 struct bio *bio,
					 struct bio_set *bs,
					 unsigned *nsegs)
{
	unsigned int max_discard_sectors, granularity;
	int alignment;
	sector_t tmp;
	unsigned split_sectors;

	*nsegs = 1;

	/* Zero-sector (unknown) and one-sector granularities are the same.  */
	granularity = max(q->limits.discard_granularity >> 9, 1U);

	max_discard_sectors = min(q->limits.max_discard_sectors, UINT_MAX >> 9);
	max_discard_sectors -= max_discard_sectors % granularity;

	if (unlikely(!max_discard_sectors)) {
		/* XXX: warn */
		return NULL;
	}

	if (bio_sectors(bio) <= max_discard_sectors)
		return NULL;

	split_sectors = max_discard_sectors;

	/*
         * If the next starting sector would be misaligned, stop the discard at
         * the previous aligned sector.
         */
	alignment = (q->limits.discard_alignment >> 9) % granularity;

	tmp = bio->bi_iter.bi_sector + split_sectors - alignment;
	tmp = sector_div(tmp, granularity);

	if (split_sectors > tmp)
		split_sectors -= tmp;

	return bio_split(bio, split_sectors, GFP_NOIO, bs);
}

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94.77%
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9
5.23%
1
50.00%
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172
100.00%
2
100.00%



static struct bio *blk_bio_write_zeroes_split(struct request_queue *q,
		struct bio *bio, struct bio_set *bs, unsigned *nsegs)
{
	*nsegs = 1;

	if (!q->limits.max_write_zeroes_sectors)
		return NULL;

	if (bio_sectors(bio) <= q->limits.max_write_zeroes_sectors)
		return NULL;

	return bio_split(bio, q->limits.max_write_zeroes_sectors, GFP_NOIO, bs);
}

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1
100.00%



static struct bio *blk_bio_write_same_split(struct request_queue *q,
					    struct bio *bio,
					    struct bio_set *bs,
					    unsigned *nsegs)
{
	*nsegs = 1;

	if (!q->limits.max_write_same_sectors)
		return NULL;

	if (bio_sectors(bio) <= q->limits.max_write_same_sectors)
		return NULL;

	return bio_split(bio, q->limits.max_write_same_sectors, GFP_NOIO, bs);
}

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67
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11.84%
1
50.00%
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76
100.00%
2
100.00%



static inline unsigned get_max_io_size(struct request_queue *q,
				       struct bio *bio)
{
	unsigned sectors = blk_max_size_offset(q, bio->bi_iter.bi_sector);
	unsigned mask = queue_logical_block_size(q) - 1;

	/* aligned to logical block size */
	sectors &= ~(mask >> 9);

	return sectors;
}

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54
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1
100.00%



static struct bio *blk_bio_segment_split(struct request_queue *q,
					 struct bio *bio,
					 struct bio_set *bs,
					 unsigned *segs)
{
	struct bio_vec bv, bvprv, *bvprvp = NULL;
	struct bvec_iter iter;
	unsigned seg_size = 0, nsegs = 0, sectors = 0;
	unsigned front_seg_size = bio->bi_seg_front_size;
	bool do_split = true;
	struct bio *new = NULL;
	const unsigned max_sectors = get_max_io_size(q, bio);
	unsigned bvecs = 0;

	bio_for_each_segment(bv, bio, iter) {
		/*
                 * With arbitrary bio size, the incoming bio may be very
                 * big. We have to split the bio into small bios so that
                 * each holds at most BIO_MAX_PAGES bvecs because
                 * bio_clone() can fail to allocate big bvecs.
                 *
                 * It should have been better to apply the limit per
                 * request queue in which bio_clone() is involved,
                 * instead of globally. The biggest blocker is the
                 * bio_clone() in bio bounce.
                 *
                 * If bio is splitted by this reason, we should have
                 * allowed to continue bios merging, but don't do
                 * that now for making the change simple.
                 *
                 * TODO: deal with bio bounce's bio_clone() gracefully
                 * and convert the global limit into per-queue limit.
                 */
		if (bvecs++ >= BIO_MAX_PAGES)
			goto split;

		/*
                 * If the queue doesn't support SG gaps and adding this
                 * offset would create a gap, disallow it.
                 */
		if (bvprvp && bvec_gap_to_prev(q, bvprvp, bv.bv_offset))
			goto split;

		if (sectors + (bv.bv_len >> 9) > max_sectors) {
			/*
                         * Consider this a new segment if we're splitting in
                         * the middle of this vector.
                         */
			if (nsegs < queue_max_segments(q) &&
			    sectors < max_sectors) {
				nsegs++;
				sectors = max_sectors;
			}
			if (sectors)
				goto split;
			/* Make this single bvec as the 1st segment */
		}

		if (bvprvp && blk_queue_cluster(q)) {
			if (seg_size + bv.bv_len > queue_max_segment_size(q))
				goto new_segment;
			if (!BIOVEC_PHYS_MERGEABLE(bvprvp, &bv))
				goto new_segment;
			if (!BIOVEC_SEG_BOUNDARY(q, bvprvp, &bv))
				goto new_segment;

			seg_size += bv.bv_len;
			bvprv = bv;
			bvprvp = &bvprv;
			sectors += bv.bv_len >> 9;

			if (nsegs == 1 && seg_size > front_seg_size)
				front_seg_size = seg_size;
			continue;
		}
new_segment:
		if (nsegs == queue_max_segments(q))
			goto split;

		nsegs++;
		bvprv = bv;
		bvprvp = &bvprv;
		seg_size = bv.bv_len;
		sectors += bv.bv_len >> 9;

		if (nsegs == 1 && seg_size > front_seg_size)
			front_seg_size = seg_size;
	}

	do_split = false;
split:
	*segs = nsegs;

	if (do_split) {
		new = bio_split(bio, sectors, GFP_NOIO, bs);
		if (new)
			bio = new;
	}

	bio->bi_seg_front_size = front_seg_size;
	if (seg_size > bio->bi_seg_back_size)
		bio->bi_seg_back_size = seg_size;

	return do_split ? new : NULL;
}

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Kent Overstreet
177
45.27%
2
18.18%
Ming Lei
145
37.08%
6
54.55%
Keith Busch
38
9.72%
1
9.09%
Lei Ming
19
4.86%
1
9.09%
Jens Axboe
12
3.07%
1
9.09%
Total
391
100.00%
11
100.00%



void blk_queue_split(struct request_queue *q, struct bio **bio,
		     struct bio_set *bs)
{
	struct bio *split, *res;
	unsigned nsegs;

	switch (bio_op(*bio)) {
	case REQ_OP_DISCARD:
	case REQ_OP_SECURE_ERASE:
		split = blk_bio_discard_split(q, *bio, bs, &nsegs);
		break;
	case REQ_OP_WRITE_ZEROES:
		split = blk_bio_write_zeroes_split(q, *bio, bs, &nsegs);
		break;
	case REQ_OP_WRITE_SAME:
		split = blk_bio_write_same_split(q, *bio, bs, &nsegs);
		break;
	default:
		split = blk_bio_segment_split(q, *bio, q->bio_split, &nsegs);
		break;
	}

	/* physical segments can be figured out during splitting */
	res = split ? split : *bio;
	res->bi_phys_segments = nsegs;
	bio_set_flag(res, BIO_SEG_VALID);

	if (split) {
		/* there isn't chance to merge the splitted bio */
		split->bi_opf |= REQ_NOMERGE;

		bio_chain(split, *bio);
		trace_block_split(q, split, (*bio)->bi_iter.bi_sector);
		generic_make_request(*bio);
		*bio = split;
	}
}
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Kent Overstreet
93
48.44%
1
11.11%
Ming Lei
44
22.92%
2
22.22%
Mike Krinkin
16
8.33%
1
11.11%
Adrian Hunter
15
7.81%
1
11.11%
Christoph Hellwig
10
5.21%
1
11.11%
Chaitanya Kulkarni
9
4.69%
1
11.11%
Michael Christie
4
2.08%
1
11.11%
Jens Axboe
1
0.52%
1
11.11%
Total
192
100.00%
9
100.00%


EXPORT_SYMBOL(blk_queue_split);



static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
					     struct bio *bio,
					     bool no_sg_merge)
{
	struct bio_vec bv, bvprv = { NULL };
	int cluster, prev = 0;
	unsigned int seg_size, nr_phys_segs;
	struct bio *fbio, *bbio;
	struct bvec_iter iter;

	if (!bio)
		return 0;

	switch (bio_op(bio)) {
	case REQ_OP_DISCARD:
	case REQ_OP_SECURE_ERASE:
	case REQ_OP_WRITE_ZEROES:
		return 0;
	case REQ_OP_WRITE_SAME:
		return 1;
	}

	fbio = bio;
	cluster = blk_queue_cluster(q);
	seg_size = 0;
	nr_phys_segs = 0;
	for_each_bio(bio) {
		bio_for_each_segment(bv, bio, iter) {
			/*
                         * If SG merging is disabled, each bio vector is
                         * a segment
                         */
			if (no_sg_merge)
				goto new_segment;

			if (prev && cluster) {
				if (seg_size + bv.bv_len
				    > queue_max_segment_size(q))
					goto new_segment;
				if (!BIOVEC_PHYS_MERGEABLE(&bvprv, &bv))
					goto new_segment;
				if (!BIOVEC_SEG_BOUNDARY(q, &bvprv, &bv))
					goto new_segment;

				seg_size += bv.bv_len;
				bvprv = bv;
				continue;
			}
new_segment:
			if (nr_phys_segs == 1 && seg_size >
			    fbio->bi_seg_front_size)
				fbio->bi_seg_front_size = seg_size;

			nr_phys_segs++;
			bvprv = bv;
			prev = 1;
			seg_size = bv.bv_len;
		}
		bbio = bio;
	}

	if (nr_phys_segs == 1 && seg_size > fbio->bi_seg_front_size)
		fbio->bi_seg_front_size = seg_size;
	if (seg_size > bbio->bi_seg_back_size)
		bbio->bi_seg_back_size = seg_size;

	return nr_phys_segs;
}

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Jens Axboe
199
72.10%
4
25.00%
Kent Overstreet
27
9.78%
3
18.75%
FUJITA Tomonori
19
6.88%
1
6.25%
Chaitanya Kulkarni
12
4.35%
1
6.25%
Christoph Hellwig
5
1.81%
1
6.25%
Michael Christie
4
1.45%
1
6.25%
Martin K. Petersen
4
1.45%
2
12.50%
Ming Lei
3
1.09%
1
6.25%
Nicholas Piggin
2
0.72%
1
6.25%
Adrian Hunter
1
0.36%
1
6.25%
Total
276
100.00%
16
100.00%



void blk_recalc_rq_segments(struct request *rq)
{
	bool no_sg_merge = !!test_bit(QUEUE_FLAG_NO_SG_MERGE,
			&rq->q->queue_flags);

	rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio,
			no_sg_merge);
}

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Jens Axboe
25
56.82%
3
75.00%
Ming Lei
19
43.18%
1
25.00%
Total
44
100.00%
4
100.00%



void blk_recount_segments(struct request_queue *q, struct bio *bio)
{
	unsigned short seg_cnt;

	/* estimate segment number by bi_vcnt for non-cloned bio */
	if (bio_flagged(bio, BIO_CLONED))
		seg_cnt = bio_segments(bio);
	else
		seg_cnt = bio->bi_vcnt;

	if (test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags) &&
			(seg_cnt < queue_max_segments(q)))
		bio->bi_phys_segments = seg_cnt;
	else {
		struct bio *nxt = bio->bi_next;

		bio->bi_next = NULL;
		bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio, false);
		bio->bi_next = nxt;
	}

	bio_set_flag(bio, BIO_SEG_VALID);
}
Contributors
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Jens Axboe
72
63.16%
4
57.14%
Lei Ming
41
35.96%
2
28.57%
Ming Lei
1
0.88%
1
14.29%
Total
114
100.00%
7
100.00%


EXPORT_SYMBOL(blk_recount_segments);



static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
				   struct bio *nxt)
{
	struct bio_vec end_bv = { NULL }, nxt_bv;

	if (!blk_queue_cluster(q))
		return 0;

	if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
	    queue_max_segment_size(q))
		return 0;

	if (!bio_has_data(bio))
		return 1;

	bio_get_last_bvec(bio, &end_bv);
	bio_get_first_bvec(nxt, &nxt_bv);

	if (!BIOVEC_PHYS_MERGEABLE(&end_bv, &nxt_bv))
		return 0;

	/*
         * bio and nxt are contiguous in memory; check if the queue allows
         * these two to be merged into one
         */
	if (BIOVEC_SEG_BOUNDARY(q, &end_bv, &nxt_bv))
		return 1;

	return 0;
}

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Jens Axboe
54
44.26%
1
11.11%
Kent Overstreet
26
21.31%
2
22.22%
David Woodhouse
25
20.49%
1
11.11%
Ming Lei
9
7.38%
1
11.11%
Martin K. Petersen
4
3.28%
2
22.22%
FUJITA Tomonori
2
1.64%
1
11.11%
Nicholas Piggin
2
1.64%
1
11.11%
Total
122
100.00%
9
100.00%


static inline void

__blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
		     struct scatterlist *sglist, struct bio_vec *bvprv,
		     struct scatterlist **sg, int *nsegs, int *cluster)
{

	int nbytes = bvec->bv_len;

	if (*sg && *cluster) {
		if ((*sg)->length + nbytes > queue_max_segment_size(q))
			goto new_segment;

		if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
			goto new_segment;
		if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
			goto new_segment;

		(*sg)->length += nbytes;
	} else {
new_segment:
		if (!*sg)
			*sg = sglist;
		else {
			/*
                         * If the driver previously mapped a shorter
                         * list, we could see a termination bit
                         * prematurely unless it fully inits the sg
                         * table on each mapping. We KNOW that there
                         * must be more entries here or the driver
                         * would be buggy, so force clear the
                         * termination bit to avoid doing a full
                         * sg_init_table() in drivers for each command.
                         */
			sg_unmark_end(*sg);
			*sg = sg_next(*sg);
		}

		sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset);
		(*nsegs)++;
	}
	*bvprv = *bvec;
}

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Jens Axboe
135
76.27%
1
20.00%
Asias He
33
18.64%
1
20.00%
Martin K. Petersen
3
1.69%
1
20.00%
Kent Overstreet
3
1.69%
1
20.00%
Paolo Bonzini
3
1.69%
1
20.00%
Total
177
100.00%
5
100.00%



static inline int __blk_bvec_map_sg(struct request_queue *q, struct bio_vec bv,
		struct scatterlist *sglist, struct scatterlist **sg)
{
	*sg = sglist;
	sg_set_page(*sg, bv.bv_page, bv.bv_len, bv.bv_offset);
	return 1;
}

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Christoph Hellwig
53
100.00%
1
100.00%
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53
100.00%
1
100.00%



static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
			     struct scatterlist *sglist,
			     struct scatterlist **sg)
{
	struct bio_vec bvec, bvprv = { NULL };
	struct bvec_iter iter;
	int cluster = blk_queue_cluster(q), nsegs = 0;

	for_each_bio(bio)
		bio_for_each_segment(bvec, bio, iter)
			__blk_segment_map_sg(q, &bvec, sglist, &bvprv, sg,
					     &nsegs, &cluster);

	return nsegs;
}

Contributors
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Tokens
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Commits
CommitProp
Asias He
58
65.17%
1
20.00%
Kent Overstreet
26
29.21%
3
60.00%
Christoph Hellwig
5
5.62%
1
20.00%
Total
89
100.00%
5
100.00%

/*
 * map a request to scatterlist, return number of sg entries setup. Caller
 * must make sure sg can hold rq->nr_phys_segments entries
 */


int blk_rq_map_sg(struct request_queue *q, struct request *rq,
		  struct scatterlist *sglist)
{
	struct scatterlist *sg = NULL;
	int nsegs = 0;

	if (rq->rq_flags & RQF_SPECIAL_PAYLOAD)
		nsegs = __blk_bvec_map_sg(q, rq->special_vec, sglist, &sg);
	else if (rq->bio && bio_op(rq->bio) == REQ_OP_WRITE_SAME)
		nsegs = __blk_bvec_map_sg(q, bio_iovec(rq->bio), sglist, &sg);
	else if (rq->bio)
		nsegs = __blk_bios_map_sg(q, rq->bio, sglist, &sg);

	if (unlikely(rq->rq_flags & RQF_COPY_USER) &&
	    (blk_rq_bytes(rq) & q->dma_pad_mask)) {
		unsigned int pad_len =
			(q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1;

		sg->length += pad_len;
		rq->extra_len += pad_len;
	}

	if (q->dma_drain_size && q->dma_drain_needed(rq)) {
		if (op_is_write(req_op(rq)))
			memset(q->dma_drain_buffer, 0, q->dma_drain_size);

		sg_unmark_end(sg);
		sg = sg_next(sg);
		sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
			    q->dma_drain_size,
			    ((unsigned long)q->dma_drain_buffer) &
			    (PAGE_SIZE - 1));
		nsegs++;
		rq->extra_len += q->dma_drain_size;
	}

	if (sg)
		sg_mark_end(sg);

	/*
         * Something must have been wrong if the figured number of
         * segment is bigger than number of req's physical segments
         */
	WARN_ON(nsegs > blk_rq_nr_phys_segments(rq));

	return nsegs;
}
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Jens Axboe
65
22.89%
1
7.69%
Christoph Hellwig
65
22.89%
2
15.38%
Kent Overstreet
53
18.66%
1
7.69%
FUJITA Tomonori
47
16.55%
2
15.38%
Tejun Heo
37
13.03%
4
30.77%
Ming Lei
8
2.82%
1
7.69%
Michael Christie
6
2.11%
1
7.69%
Dan J Williams
3
1.06%
1
7.69%
Total
284
100.00%
13
100.00%


EXPORT_SYMBOL(blk_rq_map_sg);



static inline int ll_new_hw_segment(struct request_queue *q,
				    struct request *req,
				    struct bio *bio)
{
	int nr_phys_segs = bio_phys_segments(q, bio);

	if (req->nr_phys_segments + nr_phys_segs > queue_max_segments(q))
		goto no_merge;

	if (blk_integrity_merge_bio(q, req, bio) == false)
		goto no_merge;

	/*
         * This will form the start of a new hw segment.  Bump both
         * counters.
         */
	req->nr_phys_segments += nr_phys_segs;
	return 1;

no_merge:
	req_set_nomerge(q, req);
	return 0;
}

Contributors
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Jens Axboe
45
52.33%
1
14.29%
Martin K. Petersen
34
39.53%
4
57.14%
Ritesh Harjani
5
5.81%
1
14.29%
Mikulas Patocka
2
2.33%
1
14.29%
Total
86
100.00%
7
100.00%



int ll_back_merge_fn(struct request_queue *q, struct request *req,
		     struct bio *bio)
{
	if (req_gap_back_merge(req, bio))
		return 0;
	if (blk_integrity_rq(req) &&
	    integrity_req_gap_back_merge(req, bio))
		return 0;
	if (blk_rq_sectors(req) + bio_sectors(bio) >
	    blk_rq_get_max_sectors(req, blk_rq_pos(req))) {
		req_set_nomerge(q, req);
		return 0;
	}
	if (!bio_flagged(req->biotail, BIO_SEG_VALID))
		blk_recount_segments(q, req->biotail);
	if (!bio_flagged(bio, BIO_SEG_VALID))
		blk_recount_segments(q, bio);

	return ll_new_hw_segment(q, req, bio);
}

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Jens Axboe
97
74.05%
2
28.57%
Sagi Grimberg
17
12.98%
1
14.29%
Ritesh Harjani
5
3.82%
1
14.29%
Damien Le Moal
5
3.82%
1
14.29%
Martin K. Petersen
4
3.05%
1
14.29%
Tejun Heo
3
2.29%
1
14.29%
Total
131
100.00%
7
100.00%



int ll_front_merge_fn(struct request_queue *q, struct request *req,
		      struct bio *bio)
{

	if (req_gap_front_merge(req, bio))
		return 0;
	if (blk_integrity_rq(req) &&
	    integrity_req_gap_front_merge(req, bio))
		return 0;
	if (blk_rq_sectors(req) + bio_sectors(bio) >
	    blk_rq_get_max_sectors(req, bio->bi_iter.bi_sector)) {
		req_set_nomerge(q, req);
		return 0;
	}
	if (!bio_flagged(bio, BIO_SEG_VALID))
		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);
}

Contributors
Person
Tokens
Prop
Commits
CommitProp
Jens Axboe
97
73.48%
2
28.57%
Sagi Grimberg
17
12.88%
1
14.29%
Damien Le Moal
6
4.55%
1
14.29%
Ritesh Harjani
5
3.79%
1
14.29%
Martin K. Petersen
4
3.03%
1
14.29%
Tejun Heo
3
2.27%
1
14.29%
Total
132
100.00%
7
100.00%

/*
 * 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;
}

Contributors
Person
Tokens
Prop
Commits
CommitProp
Jens Axboe
30
100.00%
1
100.00%
Total
30
100.00%
1
100.00%



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, blk_rq_pos(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;
}

Contributors
Person
Tokens
Prop
Commits
CommitProp
Jens Axboe
101
51.01%
3
23.08%
FUJITA Tomonori
50
25.25%
1
7.69%
Martin K. Petersen
23
11.62%
5
38.46%
Keith Busch
13
6.57%
2
15.38%
Tejun Heo
6
3.03%
1
7.69%
Damien Le Moal
5
2.53%
1
7.69%
Total
198
100.00%
13
100.00%

/**
 * 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->rq_flags & RQF_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