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block: Simplify blk_bio_segment_split() 

Move the max_sectors check into bvec_split_segs() such that a single
call to that function can do all the necessary checks. This patch
optimizes the fast path further, namely if a bvec fits in a page.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Hannes Reinecke <hare@suse.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Bart Van Assche 2019-08-01 15:50:43 -07:00 committed by Jens Axboe
parent ff9811b3cf
commit 708b25b344
1 changed files with 33 additions and 35 deletions
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68
block/blk-merge.c
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@ -157,22 +157,36 @@ static unsigned get_max_segment_size(const struct request_queue *q,
queue_max_segment_size(q));
}
/*
* Split the bvec @bv into segments, and update all kinds of
* variables.
/**
* 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 *sectors, unsigned max_segs,
unsigned max_sectors)
{
unsigned len = bv->bv_len;
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;
/*
* 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 && *nsegs < max_segs) {
seg_size = get_max_segment_size(q, bv->bv_offset + total_len);
seg_size = min(seg_size, len);
@ -187,8 +201,8 @@ static bool bvec_split_segs(const struct request_queue *q,
*sectors += total_len >> 9;
/* split in the middle of the bvec if len != 0 */
return !!len;
/* tell the caller to split the bvec if it is too big to fit */
return len > 0 || bv->bv_len > max_len;
}
/**
@ -229,34 +243,18 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
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,
&sectors, max_segs);
}
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;
}
if (nsegs == max_segs)
goto split;
bvprv = bv;
bvprvp = &bvprv;
if (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)) {
goto split;
}
}
*segs = nsegs;
@ -363,7 +361,7 @@ unsigned int blk_recalc_rq_segments(struct request *rq)
rq_for_each_bvec(bv, rq, iter)
bvec_split_segs(rq->q, &bv, &nr_phys_segs, &nr_sectors,
UINT_MAX);
UINT_MAX, UINT_MAX);
return nr_phys_segs;
}