linux/block/blk-merge.c
Ming Lei a1cb65377e blk-mq: only try to run plug merge if request has same queue with incoming bio
It is obvious that io merge can't be done between two different queues, so
just try to run io merge in case of same queue.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20211102133502.3619184-2-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2021-11-03 09:27:57 -06:00

1172 lines
31 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/blk-integrity.h>
#include <linux/scatterlist.h>
#include <trace/events/block.h>
#include "blk.h"
#include "blk-rq-qos.h"
#include "blk-throttle.h"
static inline void bio_get_first_bvec(struct bio *bio, struct bio_vec *bv)
{
*bv = mp_bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter);
}
static inline void bio_get_last_bvec(struct bio *bio, struct bio_vec *bv)
{
struct bvec_iter iter = bio->bi_iter;
int idx;
bio_get_first_bvec(bio, bv);
if (bv->bv_len == bio->bi_iter.bi_size)
return; /* this bio only has a single bvec */
bio_advance_iter(bio, &iter, iter.bi_size);
if (!iter.bi_bvec_done)
idx = iter.bi_idx - 1;
else /* in the middle of bvec */
idx = iter.bi_idx;
*bv = bio->bi_io_vec[idx];
/*
* iter.bi_bvec_done records actual length of the last bvec
* if this bio ends in the middle of one io vector
*/
if (iter.bi_bvec_done)
bv->bv_len = iter.bi_bvec_done;
}
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 (biovec_phys_mergeable(q, &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 = 0;
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);
}
/*
* Return the maximum number of sectors from the start of a bio that may be
* submitted as a single request to a block device. If enough sectors remain,
* align the end to the physical block size. Otherwise align the end to the
* logical block size. This approach minimizes the number of non-aligned
* requests that are submitted to a block device if the start of a bio is not
* aligned to a physical block boundary.
*/
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, 0);
unsigned max_sectors = sectors;
unsigned pbs = queue_physical_block_size(q) >> SECTOR_SHIFT;
unsigned lbs = queue_logical_block_size(q) >> SECTOR_SHIFT;
unsigned start_offset = bio->bi_iter.bi_sector & (pbs - 1);
max_sectors += start_offset;
max_sectors &= ~(pbs - 1);
if (max_sectors > start_offset)
return max_sectors - start_offset;
return sectors & ~(lbs - 1);
}
static inline unsigned get_max_segment_size(const struct request_queue *q,
struct page *start_page,
unsigned long offset)
{
unsigned long mask = queue_segment_boundary(q);
offset = mask & (page_to_phys(start_page) + offset);
/*
* overflow may be triggered in case of zero page physical address
* on 32bit arch, use queue's max segment size when that happens.
*/
return min_not_zero(mask - offset + 1,
(unsigned long)queue_max_segment_size(q));
}
/**
* bvec_split_segs - verify whether or not a bvec should be split in the middle
* @q: [in] request queue associated with the bio associated with @bv
* @bv: [in] bvec to examine
* @nsegs: [in,out] Number of segments in the bio being built. Incremented
* by the number of segments from @bv that may be appended to that
* bio without exceeding @max_segs
* @sectors: [in,out] Number of sectors in the bio being built. Incremented
* by the number of sectors from @bv that may be appended to that
* bio without exceeding @max_sectors
* @max_segs: [in] upper bound for *@nsegs
* @max_sectors: [in] upper bound for *@sectors
*
* When splitting a bio, it can happen that a bvec is encountered that is too
* big to fit in a single segment and hence that it has to be split in the
* middle. This function verifies whether or not that should happen. The value
* %true is returned if and only if appending the entire @bv to a bio with
* *@nsegs segments and *@sectors sectors would make that bio unacceptable for
* the block driver.
*/
static bool bvec_split_segs(const struct request_queue *q,
const struct bio_vec *bv, unsigned *nsegs,
unsigned *sectors, unsigned max_segs,
unsigned max_sectors)
{
unsigned max_len = (min(max_sectors, UINT_MAX >> 9) - *sectors) << 9;
unsigned len = min(bv->bv_len, max_len);
unsigned total_len = 0;
unsigned seg_size = 0;
while (len && *nsegs < max_segs) {
seg_size = get_max_segment_size(q, bv->bv_page,
bv->bv_offset + total_len);
seg_size = min(seg_size, len);
(*nsegs)++;
total_len += seg_size;
len -= seg_size;
if ((bv->bv_offset + total_len) & queue_virt_boundary(q))
break;
}
*sectors += total_len >> 9;
/* tell the caller to split the bvec if it is too big to fit */
return len > 0 || bv->bv_len > max_len;
}
/**
* blk_bio_segment_split - split a bio in two bios
* @q: [in] request queue pointer
* @bio: [in] bio to be split
* @bs: [in] bio set to allocate the clone from
* @segs: [out] number of segments in the bio with the first half of the sectors
*
* Clone @bio, update the bi_iter of the clone to represent the first sectors
* of @bio and update @bio->bi_iter to represent the remaining sectors. The
* following is guaranteed for the cloned bio:
* - That it has at most get_max_io_size(@q, @bio) sectors.
* - That it has at most queue_max_segments(@q) segments.
*
* Except for discard requests the cloned bio will point at the bi_io_vec of
* the original bio. It is the responsibility of the caller to ensure that the
* original bio is not freed before the cloned bio. The caller is also
* responsible for ensuring that @bs is only destroyed after processing of the
* split bio has finished.
*/
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 nsegs = 0, sectors = 0;
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 (nsegs < max_segs &&
sectors + (bv.bv_len >> 9) <= max_sectors &&
bv.bv_offset + bv.bv_len <= PAGE_SIZE) {
nsegs++;
sectors += bv.bv_len >> 9;
} else if (bvec_split_segs(q, &bv, &nsegs, &sectors, max_segs,
max_sectors)) {
goto split;
}
bvprv = bv;
bvprvp = &bvprv;
}
*segs = nsegs;
return NULL;
split:
*segs = nsegs;
/*
* Bio splitting may cause subtle trouble such as hang when doing sync
* iopoll in direct IO routine. Given performance gain of iopoll for
* big IO can be trival, disable iopoll when split needed.
*/
bio_clear_polled(bio);
return bio_split(bio, sectors, GFP_NOIO, bs);
}
/**
* __blk_queue_split - split a bio and submit the second half
* @q: [in] request_queue new bio is being queued at
* @bio: [in, out] bio to be split
* @nr_segs: [out] number of segments in the first bio
*
* Split a bio into two bios, chain the two bios, submit the second half and
* store a pointer to the first half in *@bio. If the second bio is still too
* big it will be split by a recursive call to this function. Since this
* function may allocate a new bio from q->bio_split, it is the responsibility
* of the caller to ensure that q->bio_split is only released after processing
* of the split bio has finished.
*/
void __blk_queue_split(struct request_queue *q, struct bio **bio,
unsigned int *nr_segs)
{
struct bio *split = NULL;
switch (bio_op(*bio)) {
case REQ_OP_DISCARD:
case REQ_OP_SECURE_ERASE:
split = blk_bio_discard_split(q, *bio, &q->bio_split, nr_segs);
break;
case REQ_OP_WRITE_ZEROES:
split = blk_bio_write_zeroes_split(q, *bio, &q->bio_split,
nr_segs);
break;
case REQ_OP_WRITE_SAME:
split = blk_bio_write_same_split(q, *bio, &q->bio_split,
nr_segs);
break;
default:
split = blk_bio_segment_split(q, *bio, &q->bio_split, nr_segs);
break;
}
if (split) {
/* there isn't chance to merge the splitted bio */
split->bi_opf |= REQ_NOMERGE;
bio_chain(split, *bio);
trace_block_split(split, (*bio)->bi_iter.bi_sector);
submit_bio_noacct(*bio);
*bio = split;
blk_throtl_charge_bio_split(*bio);
}
}
/**
* blk_queue_split - split a bio and submit the second half
* @bio: [in, out] bio to be split
*
* Split a bio into two bios, chains the two bios, submit the second half and
* store a pointer to the first half in *@bio. Since this function may allocate
* a new bio from q->bio_split, it is the responsibility of the caller to ensure
* that q->bio_split is only released after processing of the split bio has
* finished.
*/
void blk_queue_split(struct bio **bio)
{
struct request_queue *q = bdev_get_queue((*bio)->bi_bdev);
unsigned int nr_segs;
if (blk_may_split(q, *bio))
__blk_queue_split(q, bio, &nr_segs);
}
EXPORT_SYMBOL(blk_queue_split);
unsigned int blk_recalc_rq_segments(struct request *rq)
{
unsigned int nr_phys_segs = 0;
unsigned int nr_sectors = 0;
struct req_iterator iter;
struct bio_vec bv;
if (!rq->bio)
return 0;
switch (bio_op(rq->bio)) {
case REQ_OP_DISCARD:
case REQ_OP_SECURE_ERASE:
if (queue_max_discard_segments(rq->q) > 1) {
struct bio *bio = rq->bio;
for_each_bio(bio)
nr_phys_segs++;
return nr_phys_segs;
}
return 1;
case REQ_OP_WRITE_ZEROES:
return 0;
case REQ_OP_WRITE_SAME:
return 1;
}
rq_for_each_bvec(bv, rq, iter)
bvec_split_segs(rq->q, &bv, &nr_phys_segs, &nr_sectors,
UINT_MAX, UINT_MAX);
return nr_phys_segs;
}
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;
while (nbytes > 0) {
unsigned offset = bvec->bv_offset + total;
unsigned len = min(get_max_segment_size(q, bvec->bv_page,
offset), nbytes);
struct page *page = bvec->bv_page;
/*
* Unfortunately a fair number of drivers barf on scatterlists
* that have an offset larger than PAGE_SIZE, despite other
* subsystems dealing with that invariant just fine. For now
* stick to the legacy format where we never present those from
* the block layer, but the code below should be removed once
* these offenders (mostly MMC/SD drivers) are fixed.
*/
page += (offset >> PAGE_SHIFT);
offset &= ~PAGE_MASK;
*sg = blk_next_sg(sg, sglist);
sg_set_page(*sg, page, len, offset);
total += len;
nbytes -= len;
nsegs++;
}
return nsegs;
}
static inline int __blk_bvec_map_sg(struct bio_vec bv,
struct scatterlist *sglist, struct scatterlist **sg)
{
*sg = blk_next_sg(sg, sglist);
sg_set_page(*sg, bv.bv_page, bv.bv_len, bv.bv_offset);
return 1;
}
/* only try to merge bvecs into one sg if they are from two bios */
static inline bool
__blk_segment_map_sg_merge(struct request_queue *q, struct bio_vec *bvec,
struct bio_vec *bvprv, struct scatterlist **sg)
{
int nbytes = bvec->bv_len;
if (!*sg)
return false;
if ((*sg)->length + nbytes > queue_max_segment_size(q))
return false;
if (!biovec_phys_mergeable(q, bvprv, bvec))
return false;
(*sg)->length += nbytes;
return true;
}
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;
bool new_bio = false;
for_each_bio(bio) {
bio_for_each_bvec(bvec, bio, iter) {
/*
* Only try to merge bvecs from two bios given we
* have done bio internal merge when adding pages
* to bio
*/
if (new_bio &&
__blk_segment_map_sg_merge(q, &bvec, &bvprv, sg))
goto next_bvec;
if (bvec.bv_offset + bvec.bv_len <= PAGE_SIZE)
nsegs += __blk_bvec_map_sg(bvec, sglist, sg);
else
nsegs += blk_bvec_map_sg(q, &bvec, sglist, sg);
next_bvec:
new_bio = false;
}
if (likely(bio->bi_iter.bi_size)) {
bvprv = bvec;
new_bio = true;
}
}
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 **last_sg)
{
int nsegs = 0;
if (rq->rq_flags & RQF_SPECIAL_PAYLOAD)
nsegs = __blk_bvec_map_sg(rq->special_vec, sglist, last_sg);
else if (rq->bio && bio_op(rq->bio) == REQ_OP_WRITE_SAME)
nsegs = __blk_bvec_map_sg(bio_iovec(rq->bio), sglist, last_sg);
else if (rq->bio)
nsegs = __blk_bios_map_sg(q, rq->bio, sglist, last_sg);
if (*last_sg)
sg_mark_end(*last_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 unsigned int blk_rq_get_max_segments(struct request *rq)
{
if (req_op(rq) == REQ_OP_DISCARD)
return queue_max_discard_segments(rq->q);
return queue_max_segments(rq->q);
}
static inline unsigned int blk_rq_get_max_sectors(struct request *rq,
sector_t offset)
{
struct request_queue *q = rq->q;
if (blk_rq_is_passthrough(rq))
return q->limits.max_hw_sectors;
if (!q->limits.chunk_sectors ||
req_op(rq) == REQ_OP_DISCARD ||
req_op(rq) == REQ_OP_SECURE_ERASE)
return blk_queue_get_max_sectors(q, req_op(rq));
return min(blk_max_size_offset(q, offset, 0),
blk_queue_get_max_sectors(q, req_op(rq)));
}
static inline int ll_new_hw_segment(struct request *req, struct bio *bio,
unsigned int nr_phys_segs)
{
if (blk_integrity_merge_bio(req->q, req, bio) == false)
goto no_merge;
/* discard request merge won't add new segment */
if (req_op(req) == REQ_OP_DISCARD)
return 1;
if (req->nr_phys_segments + nr_phys_segs > blk_rq_get_max_segments(req))
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(req->q, req);
return 0;
}
int ll_back_merge_fn(struct request *req, struct bio *bio, unsigned int nr_segs)
{
if (req_gap_back_merge(req, bio))
return 0;
if (blk_integrity_rq(req) &&
integrity_req_gap_back_merge(req, bio))
return 0;
if (!bio_crypt_ctx_back_mergeable(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(req->q, req);
return 0;
}
return ll_new_hw_segment(req, bio, nr_segs);
}
static int ll_front_merge_fn(struct request *req, struct bio *bio,
unsigned int nr_segs)
{
if (req_gap_front_merge(req, bio))
return 0;
if (blk_integrity_rq(req) &&
integrity_req_gap_front_merge(req, bio))
return 0;
if (!bio_crypt_ctx_front_mergeable(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(req->q, req);
return 0;
}
return ll_new_hw_segment(req, bio, nr_segs);
}
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;
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 (total_phys_segments > blk_rq_get_max_segments(req))
return 0;
if (blk_integrity_merge_rq(q, req, next) == false)
return 0;
if (!bio_crypt_ctx_merge_rq(req, next))
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_request(struct request *req)
{
if (blk_do_io_stat(req)) {
part_stat_lock();
part_stat_inc(req->part, merges[op_stat_group(req_op(req))]);
part_stat_unlock();
}
}
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;
}
static inline bool blk_write_same_mergeable(struct bio *a, struct bio *b)
{
if (bio_page(a) == bio_page(b) && bio_offset(a) == bio_offset(b))
return true;
return false;
}
/*
* 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_request(next);
trace_block_rq_merge(next);
/*
* ownership of bio passed from next to req, return 'next' for
* the caller to free
*/
next->bio = NULL;
return next;
}
static 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;
}
static 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;
}
/*
* Try to merge 'next' into 'rq'. Return true if the merge happened, false
* otherwise. The caller is responsible for freeing 'next' if the merge
* happened.
*/
bool 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 (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_bdev->bd_disk)
return false;
/* only merge integrity protected bio into ditto rq */
if (blk_integrity_merge_bio(rq->q, rq, bio) == false)
return false;
/* Only merge if the crypt contexts are compatible */
if (!bio_crypt_rq_ctx_compatible(rq, bio))
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;
}
static void blk_account_io_merge_bio(struct request *req)
{
if (!blk_do_io_stat(req))
return;
part_stat_lock();
part_stat_inc(req->part, merges[op_stat_group(req_op(req))]);
part_stat_unlock();
}
enum bio_merge_status {
BIO_MERGE_OK,
BIO_MERGE_NONE,
BIO_MERGE_FAILED,
};
static enum bio_merge_status bio_attempt_back_merge(struct request *req,
struct bio *bio, unsigned int nr_segs)
{
const int ff = bio->bi_opf & REQ_FAILFAST_MASK;
if (!ll_back_merge_fn(req, bio, nr_segs))
return BIO_MERGE_FAILED;
trace_block_bio_backmerge(bio);
rq_qos_merge(req->q, req, bio);
if ((req->cmd_flags & REQ_FAILFAST_MASK) != ff)
blk_rq_set_mixed_merge(req);
req->biotail->bi_next = bio;
req->biotail = bio;
req->__data_len += bio->bi_iter.bi_size;
bio_crypt_free_ctx(bio);
blk_account_io_merge_bio(req);
return BIO_MERGE_OK;
}
static enum bio_merge_status bio_attempt_front_merge(struct request *req,
struct bio *bio, unsigned int nr_segs)
{
const int ff = bio->bi_opf & REQ_FAILFAST_MASK;
if (!ll_front_merge_fn(req, bio, nr_segs))
return BIO_MERGE_FAILED;
trace_block_bio_frontmerge(bio);
rq_qos_merge(req->q, req, bio);
if ((req->cmd_flags & REQ_FAILFAST_MASK) != ff)
blk_rq_set_mixed_merge(req);
bio->bi_next = req->bio;
req->bio = bio;
req->__sector = bio->bi_iter.bi_sector;
req->__data_len += bio->bi_iter.bi_size;
bio_crypt_do_front_merge(req, bio);
blk_account_io_merge_bio(req);
return BIO_MERGE_OK;
}
static enum bio_merge_status bio_attempt_discard_merge(struct request_queue *q,
struct request *req, struct bio *bio)
{
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(bio) >
blk_rq_get_max_sectors(req, blk_rq_pos(req)))
goto no_merge;
rq_qos_merge(q, req, bio);
req->biotail->bi_next = bio;
req->biotail = bio;
req->__data_len += bio->bi_iter.bi_size;
req->nr_phys_segments = segments + 1;
blk_account_io_merge_bio(req);
return BIO_MERGE_OK;
no_merge:
req_set_nomerge(q, req);
return BIO_MERGE_FAILED;
}
static enum bio_merge_status blk_attempt_bio_merge(struct request_queue *q,
struct request *rq,
struct bio *bio,
unsigned int nr_segs,
bool sched_allow_merge)
{
if (!blk_rq_merge_ok(rq, bio))
return BIO_MERGE_NONE;
switch (blk_try_merge(rq, bio)) {
case ELEVATOR_BACK_MERGE:
if (!sched_allow_merge || blk_mq_sched_allow_merge(q, rq, bio))
return bio_attempt_back_merge(rq, bio, nr_segs);
break;
case ELEVATOR_FRONT_MERGE:
if (!sched_allow_merge || blk_mq_sched_allow_merge(q, rq, bio))
return bio_attempt_front_merge(rq, bio, nr_segs);
break;
case ELEVATOR_DISCARD_MERGE:
return bio_attempt_discard_merge(q, rq, bio);
default:
return BIO_MERGE_NONE;
}
return BIO_MERGE_FAILED;
}
/**
* blk_attempt_plug_merge - try to merge with %current's plugged list
* @q: request_queue new bio is being queued at
* @bio: new bio being queued
* @nr_segs: number of segments in @bio
* @same_queue_rq: output value, will be true if there's an existing request
* from the passed in @q already in the plug list
*
* Determine whether @bio being queued on @q can be merged with the previous
* request on %current's plugged list. Returns %true if merge was successful,
* otherwise %false.
*
* Plugging coalesces IOs from the same issuer for the same purpose without
* going through @q->queue_lock. As such it's more of an issuing mechanism
* than scheduling, and the request, while may have elvpriv data, is not
* added on the elevator at this point. In addition, we don't have
* reliable access to the elevator outside queue lock. Only check basic
* merging parameters without querying the elevator.
*
* Caller must ensure !blk_queue_nomerges(q) beforehand.
*/
bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
unsigned int nr_segs, bool *same_queue_rq)
{
struct blk_plug *plug;
struct request *rq;
plug = blk_mq_plug(q, bio);
if (!plug || rq_list_empty(plug->mq_list))
return false;
/* check the previously added entry for a quick merge attempt */
rq = rq_list_peek(&plug->mq_list);
if (rq->q == q) {
/*
* Only blk-mq multiple hardware queues case checks the rq in
* the same queue, there should be only one such rq in a queue
*/
*same_queue_rq = true;
if (blk_attempt_bio_merge(q, rq, bio, nr_segs, false) ==
BIO_MERGE_OK)
return true;
}
return false;
}
/*
* Iterate list of requests and see if we can merge this bio with any
* of them.
*/
bool blk_bio_list_merge(struct request_queue *q, struct list_head *list,
struct bio *bio, unsigned int nr_segs)
{
struct request *rq;
int checked = 8;
list_for_each_entry_reverse(rq, list, queuelist) {
if (!checked--)
break;
switch (blk_attempt_bio_merge(q, rq, bio, nr_segs, true)) {
case BIO_MERGE_NONE:
continue;
case BIO_MERGE_OK:
return true;
case BIO_MERGE_FAILED:
return false;
}
}
return false;
}
EXPORT_SYMBOL_GPL(blk_bio_list_merge);
bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,
unsigned int nr_segs, struct request **merged_request)
{
struct request *rq;
switch (elv_merge(q, &rq, bio)) {
case ELEVATOR_BACK_MERGE:
if (!blk_mq_sched_allow_merge(q, rq, bio))
return false;
if (bio_attempt_back_merge(rq, bio, nr_segs) != BIO_MERGE_OK)
return false;
*merged_request = attempt_back_merge(q, rq);
if (!*merged_request)
elv_merged_request(q, rq, ELEVATOR_BACK_MERGE);
return true;
case ELEVATOR_FRONT_MERGE:
if (!blk_mq_sched_allow_merge(q, rq, bio))
return false;
if (bio_attempt_front_merge(rq, bio, nr_segs) != BIO_MERGE_OK)
return false;
*merged_request = attempt_front_merge(q, rq);
if (!*merged_request)
elv_merged_request(q, rq, ELEVATOR_FRONT_MERGE);
return true;
case ELEVATOR_DISCARD_MERGE:
return bio_attempt_discard_merge(q, rq, bio) == BIO_MERGE_OK;
default:
return false;
}
}
EXPORT_SYMBOL_GPL(blk_mq_sched_try_merge);