linux/block/blk-merge.c
Ming Lei 05b700ba60 block: fix segment calculation for passthrough IO
blk_recount_segments() can be called in bio_add_pc_page() for
calculating how many segments this bio will has after one page is added
to this bio. If the resulted segment number is beyond the queue limit,
the added page will be removed.

The try-and-fix policy requires blk_recount_segments(__blk_recalc_rq_segments)
to not consider the segment number limit. Unfortunately bvec_split_segs()
does check this limit, and causes small segment number returned to
bio_add_pc_page(), then page still may be added to the bio even though
segment number limit becomes broken.

Fixes this issue by not considering segment number limit when calcualting
bio's segment number.

Fixes: dcebd75592 ("block: use bio_for_each_bvec() to compute multi-page bvec count")
Cc: Christoph Hellwig <hch@lst.de>
Cc: Omar Sandoval <osandov@fb.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-03-06 09:42:54 -07:00

986 lines
24 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* 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"
/*
* Check if the two bvecs from two bios can be merged to one segment. If yes,
* no need to check gap between the two bios since the 1st bio and the 1st bvec
* in the 2nd bio can be handled in one segment.
*/
static inline bool bios_segs_mergeable(struct request_queue *q,
struct bio *prev, struct bio_vec *prev_last_bv,
struct bio_vec *next_first_bv)
{
if (!biovec_phys_mergeable(q, prev_last_bv, next_first_bv))
return false;
if (prev->bi_seg_back_size + next_first_bv->bv_len >
queue_max_segment_size(q))
return false;
return true;
}
static inline bool bio_will_gap(struct request_queue *q,
struct request *prev_rq, struct bio *prev, struct bio *next)
{
struct bio_vec pb, nb;
if (!bio_has_data(prev) || !queue_virt_boundary(q))
return false;
/*
* Don't merge if the 1st bio starts with non-zero offset, otherwise it
* is quite difficult to respect the sg gap limit. We work hard to
* merge a huge number of small single bios in case of mkfs.
*/
if (prev_rq)
bio_get_first_bvec(prev_rq->bio, &pb);
else
bio_get_first_bvec(prev, &pb);
if (pb.bv_offset & queue_virt_boundary(q))
return true;
/*
* We don't need to worry about the situation that the merged segment
* ends in unaligned virt boundary:
*
* - if 'pb' ends aligned, the merged segment ends aligned
* - if 'pb' ends unaligned, the next bio must include
* one single bvec of 'nb', otherwise the 'nb' can't
* merge with 'pb'
*/
bio_get_last_bvec(prev, &pb);
bio_get_first_bvec(next, &nb);
if (bios_segs_mergeable(q, prev, &pb, &nb))
return false;
return __bvec_gap_to_prev(q, &pb, nb.bv_offset);
}
static inline bool req_gap_back_merge(struct request *req, struct bio *bio)
{
return bio_will_gap(req->q, req, req->biotail, bio);
}
static inline bool req_gap_front_merge(struct request *req, struct bio *bio)
{
return bio_will_gap(req->q, NULL, bio, req->bio);
}
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,
bio_allowed_max_sectors(q));
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);
}
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);
}
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);
}
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;
}
static unsigned get_max_segment_size(struct request_queue *q,
unsigned offset)
{
unsigned long mask = queue_segment_boundary(q);
/* default segment boundary mask means no boundary limit */
if (mask == BLK_SEG_BOUNDARY_MASK)
return queue_max_segment_size(q);
return min_t(unsigned long, mask - (mask & offset) + 1,
queue_max_segment_size(q));
}
/*
* Split the bvec @bv into segments, and update all kinds of
* variables.
*/
static bool bvec_split_segs(struct request_queue *q, struct bio_vec *bv,
unsigned *nsegs, unsigned *last_seg_size,
unsigned *front_seg_size, unsigned *sectors, unsigned max_segs)
{
unsigned len = bv->bv_len;
unsigned total_len = 0;
unsigned new_nsegs = 0, seg_size = 0;
/*
* Multi-page bvec may be too big to hold in one segment, so the
* current bvec has to be splitted as multiple segments.
*/
while (len && new_nsegs + *nsegs < max_segs) {
seg_size = get_max_segment_size(q, bv->bv_offset + total_len);
seg_size = min(seg_size, len);
new_nsegs++;
total_len += seg_size;
len -= seg_size;
if ((bv->bv_offset + total_len) & queue_virt_boundary(q))
break;
}
if (!new_nsegs)
return !!len;
/* update front segment size */
if (!*nsegs) {
unsigned first_seg_size;
if (new_nsegs == 1)
first_seg_size = get_max_segment_size(q, bv->bv_offset);
else
first_seg_size = queue_max_segment_size(q);
if (*front_seg_size < first_seg_size)
*front_seg_size = first_seg_size;
}
/* update other varibles */
*last_seg_size = seg_size;
*nsegs += new_nsegs;
if (sectors)
*sectors += total_len >> 9;
/* split in the middle of the bvec if len != 0 */
return !!len;
}
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);
const unsigned max_segs = queue_max_segments(q);
bio_for_each_bvec(bv, bio, iter) {
/*
* 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 < max_segs &&
sectors < max_sectors) {
/* split in the middle of bvec */
bv.bv_len = (max_sectors - sectors) << 9;
bvec_split_segs(q, &bv, &nsegs,
&seg_size,
&front_seg_size,
&sectors, max_segs);
}
goto split;
}
if (bvprvp) {
if (seg_size + bv.bv_len > queue_max_segment_size(q))
goto new_segment;
if (!biovec_phys_mergeable(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 == max_segs)
goto split;
bvprv = bv;
bvprvp = &bvprv;
if (bv.bv_offset + bv.bv_len <= PAGE_SIZE) {
nsegs++;
seg_size = bv.bv_len;
sectors += bv.bv_len >> 9;
if (nsegs == 1 && seg_size > front_seg_size)
front_seg_size = seg_size;
} else if (bvec_split_segs(q, &bv, &nsegs, &seg_size,
&front_seg_size, &sectors, max_segs)) {
goto split;
}
}
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;
}
void blk_queue_split(struct request_queue *q, struct bio **bio)
{
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, &q->bio_split, &nsegs);
break;
case REQ_OP_WRITE_ZEROES:
split = blk_bio_write_zeroes_split(q, *bio, &q->bio_split, &nsegs);
break;
case REQ_OP_WRITE_SAME:
split = blk_bio_write_same_split(q, *bio, &q->bio_split, &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;
/*
* Since we're recursing into make_request here, ensure
* that we mark this bio as already having entered the queue.
* If not, and the queue is going away, we can get stuck
* forever on waiting for the queue reference to drop. But
* that will never happen, as we're already holding a
* reference to it.
*/
bio_set_flag(*bio, BIO_QUEUE_ENTERED);
bio_chain(split, *bio);
trace_block_split(q, split, (*bio)->bi_iter.bi_sector);
generic_make_request(*bio);
*bio = split;
}
}
EXPORT_SYMBOL(blk_queue_split);
static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
struct bio *bio)
{
struct bio_vec bv, bvprv = { NULL };
int prev = 0;
unsigned int seg_size, nr_phys_segs;
unsigned front_seg_size;
struct bio *fbio, *bbio;
struct bvec_iter iter;
if (!bio)
return 0;
front_seg_size = bio->bi_seg_front_size;
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;
seg_size = 0;
nr_phys_segs = 0;
for_each_bio(bio) {
bio_for_each_bvec(bv, bio, iter) {
if (prev) {
if (seg_size + bv.bv_len
> queue_max_segment_size(q))
goto new_segment;
if (!biovec_phys_mergeable(q, &bvprv, &bv))
goto new_segment;
seg_size += bv.bv_len;
bvprv = bv;
if (nr_phys_segs == 1 && seg_size >
front_seg_size)
front_seg_size = seg_size;
continue;
}
new_segment:
bvprv = bv;
prev = 1;
bvec_split_segs(q, &bv, &nr_phys_segs, &seg_size,
&front_seg_size, NULL, UINT_MAX);
}
bbio = bio;
}
fbio->bi_seg_front_size = front_seg_size;
if (seg_size > bbio->bi_seg_back_size)
bbio->bi_seg_back_size = seg_size;
return nr_phys_segs;
}
void blk_recalc_rq_segments(struct request *rq)
{
rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio);
}
void blk_recount_segments(struct request_queue *q, struct bio *bio)
{
struct bio *nxt = bio->bi_next;
bio->bi_next = NULL;
bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio);
bio->bi_next = nxt;
bio_set_flag(bio, BIO_SEG_VALID);
}
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 (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);
return biovec_phys_mergeable(q, &end_bv, &nxt_bv);
}
static inline struct scatterlist *blk_next_sg(struct scatterlist **sg,
struct scatterlist *sglist)
{
if (!*sg)
return sglist;
/*
* 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);
return sg_next(*sg);
}
static unsigned blk_bvec_map_sg(struct request_queue *q,
struct bio_vec *bvec, struct scatterlist *sglist,
struct scatterlist **sg)
{
unsigned nbytes = bvec->bv_len;
unsigned nsegs = 0, total = 0, offset = 0;
while (nbytes > 0) {
unsigned seg_size;
struct page *pg;
unsigned idx;
*sg = blk_next_sg(sg, sglist);
seg_size = get_max_segment_size(q, bvec->bv_offset + total);
seg_size = min(nbytes, seg_size);
offset = (total + bvec->bv_offset) % PAGE_SIZE;
idx = (total + bvec->bv_offset) / PAGE_SIZE;
pg = bvec_nth_page(bvec->bv_page, idx);
sg_set_page(*sg, pg, seg_size, offset);
total += seg_size;
nbytes -= seg_size;
nsegs++;
}
return nsegs;
}
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 nbytes = bvec->bv_len;
if (*sg) {
if ((*sg)->length + nbytes > queue_max_segment_size(q))
goto new_segment;
if (!biovec_phys_mergeable(q, bvprv, bvec))
goto new_segment;
(*sg)->length += nbytes;
} else {
new_segment:
if (bvec->bv_offset + bvec->bv_len <= PAGE_SIZE) {
*sg = blk_next_sg(sg, sglist);
sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset);
(*nsegs) += 1;
} else
(*nsegs) += blk_bvec_map_sg(q, bvec, sglist, sg);
}
*bvprv = *bvec;
}
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;
}
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 nsegs = 0;
for_each_bio(bio)
bio_for_each_bvec(bvec, bio, iter)
__blk_segment_map_sg(q, &bvec, sglist, &bvprv, sg,
&nsegs);
return nsegs;
}
/*
* 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;
}
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;
}
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);
}
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);
}
static bool req_attempt_discard_merge(struct request_queue *q, struct request *req,
struct request *next)
{
unsigned short segments = blk_rq_nr_discard_segments(req);
if (segments >= queue_max_discard_segments(q))
goto no_merge;
if (blk_rq_sectors(req) + bio_sectors(next->bio) >
blk_rq_get_max_sectors(req, blk_rq_pos(req)))
goto no_merge;
req->nr_phys_segments = segments + blk_rq_nr_discard_segments(next);
return true;
no_merge:
req_set_nomerge(q, req);
return false;
}
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;
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;
}
/**
* 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->bi_next) {
WARN_ON_ONCE((bio->bi_opf & REQ_FAILFAST_MASK) &&
(bio->bi_opf & REQ_FAILFAST_MASK) != ff);
bio->bi_opf |= ff;
}
rq->rq_flags |= RQF_MIXED_MERGE;
}
static void blk_account_io_merge(struct request *req)
{
if (blk_do_io_stat(req)) {
struct hd_struct *part;
part_stat_lock();
part = req->part;
part_dec_in_flight(req->q, part, rq_data_dir(req));
hd_struct_put(part);
part_stat_unlock();
}
}
/*
* Two cases of handling DISCARD merge:
* If max_discard_segments > 1, the driver takes every bio
* as a range and send them to controller together. The ranges
* needn't to be contiguous.
* Otherwise, the bios/requests will be handled as same as
* others which should be contiguous.
*/
static inline bool blk_discard_mergable(struct request *req)
{
if (req_op(req) == REQ_OP_DISCARD &&
queue_max_discard_segments(req->q) > 1)
return true;
return false;
}
static enum elv_merge blk_try_req_merge(struct request *req,
struct request *next)
{
if (blk_discard_mergable(req))
return ELEVATOR_DISCARD_MERGE;
else if (blk_rq_pos(req) + blk_rq_sectors(req) == blk_rq_pos(next))
return ELEVATOR_BACK_MERGE;
return ELEVATOR_NO_MERGE;
}
/*
* For non-mq, this has to be called with the request spinlock acquired.
* For mq with scheduling, the appropriate queue wide lock should be held.
*/
static struct request *attempt_merge(struct request_queue *q,
struct request *req, struct request *next)
{
if (!rq_mergeable(req) || !rq_mergeable(next))
return NULL;
if (req_op(req) != req_op(next))
return NULL;
if (rq_data_dir(req) != rq_data_dir(next)
|| req->rq_disk != next->rq_disk)
return NULL;
if (req_op(req) == REQ_OP_WRITE_SAME &&
!blk_write_same_mergeable(req->bio, next->bio))
return NULL;
/*
* Don't allow merge of different write hints, or for a hint with
* non-hint IO.
*/
if (req->write_hint != next->write_hint)
return NULL;
if (req->ioprio != next->ioprio)
return NULL;
/*
* 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. Handle DISCARDs separately, as they
* have separate settings.
*/
switch (blk_try_req_merge(req, next)) {
case ELEVATOR_DISCARD_MERGE:
if (!req_attempt_discard_merge(q, req, next))
return NULL;
break;
case ELEVATOR_BACK_MERGE:
if (!ll_merge_requests_fn(q, req, next))
return NULL;
break;
default:
return NULL;
}
/*
* 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->rq_flags | next->rq_flags) & RQF_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_ns of the merged requests to be the
* current request for accounting purposes.
*/
if (next->start_time_ns < req->start_time_ns)
req->start_time_ns = next->start_time_ns;
req->biotail->bi_next = next->bio;
req->biotail = next->biotail;
req->__data_len += blk_rq_bytes(next);
if (!blk_discard_mergable(req))
elv_merge_requests(q, req, next);
/*
* 'next' is going away, so update stats accordingly
*/
blk_account_io_merge(next);
/*
* ownership of bio passed from next to req, return 'next' for
* the caller to free
*/
next->bio = NULL;
return next;
}
struct request *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 NULL;
}
struct request *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 NULL;
}
int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
struct request *next)
{
struct request *free;
free = attempt_merge(q, rq, next);
if (free) {
blk_put_request(free);
return 1;
}
return 0;
}
bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
{
if (!rq_mergeable(rq) || !bio_mergeable(bio))
return false;
if (req_op(rq) != bio_op(bio))
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 */
if (rq->rq_disk != bio->bi_disk)
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 (req_op(rq) == REQ_OP_WRITE_SAME &&
!blk_write_same_mergeable(rq->bio, bio))
return false;
/*
* Don't allow merge of different write hints, or for a hint with
* non-hint IO.
*/
if (rq->write_hint != bio->bi_write_hint)
return false;
if (rq->ioprio != bio_prio(bio))
return false;
return true;
}
enum elv_merge blk_try_merge(struct request *rq, struct bio *bio)
{
if (blk_discard_mergable(rq))
return ELEVATOR_DISCARD_MERGE;
else 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;
}