[PATCHv4 6/9] block/merge: count bytes instead of sectors

Keith Busch
2022-05-26T01:08:48Z

From: Keith Busch <kbusch@kernel.org>

Individual bv_len's may not be a sector size.

Signed-off-by: Keith Busch <kbusch@kernel.org>
---
v3->v4:

Use sector shift

Add comment explaing the ALIGN_DOWN

block/blk-merge.c | 41 ++++++++++++++++++++++++-----------------
1 file changed, 24 insertions(+), 17 deletions(-)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 7771dacc99cb..9ff0cb9e4840 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -201,11 +201,11 @@ static inline unsigned get_max_segment_size(const struct request_queue *q,
* @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
+ * @bytes: [in,out] Number of bytes in the bio being built. Incremented
+ * by the number of bytes from @bv that may be appended to that
+ * bio without exceeding @max_bytes
* @max_segs: [in] upper bound for *@nsegs
- * @max_sectors: [in] upper bound for *@sectors
+ * @max_bytes: [in] upper bound for *@bytes
*
* 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
@@ -216,10 +216,10 @@ static inline unsigned get_max_segment_size(const struct request_queue *q,
*/
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 *bytes, unsigned max_segs,
+ unsigned max_bytes)
{
- unsigned max_len = (min(max_sectors, UINT_MAX >> 9) - *sectors) << 9;
+ unsigned max_len = min(max_bytes, UINT_MAX) - *bytes;
unsigned len = min(bv->bv_len, max_len);
unsigned total_len = 0;
unsigned seg_size = 0;
@@ -237,7 +237,7 @@ static bool bvec_split_segs(const struct request_queue *q,
break;
}

- *sectors += total_len >> 9;
+ *bytes += total_len;

/* tell the caller to split the bvec if it is too big to fit */
return len > 0 || bv->bv_len > max_len;
@@ -269,8 +269,8 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
{
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);
+ unsigned nsegs = 0, bytes = 0;
+ const unsigned max_bytes = get_max_io_size(q, bio) << 9;
const unsigned max_segs = queue_max_segments(q);

bio_for_each_bvec(bv, bio, iter) {
@@ -282,12 +282,12 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
goto split;

if (nsegs < max_segs &&
- sectors + (bv.bv_len >> 9) <= max_sectors &&
+ bytes + bv.bv_len <= max_bytes &&
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)) {
+ bytes += bv.bv_len;
+ } else if (bvec_split_segs(q, &bv, &nsegs, &bytes, max_segs,
+ max_bytes)) {
goto split;
}

@@ -300,13 +300,20 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
split:
*segs = nsegs;

+ /*
+ * Individual bvecs may not be logical block aligned, so round down to
+ * that size to ensure both sides of the split bio are appropriately
+ * sized.
+ */
+ bytes = ALIGN_DOWN(bytes, queue_logical_block_size(q));
+
/*
* 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);
+ return bio_split(bio, bytes >> SECTOR_SHIFT, GFP_NOIO, bs);
}

/**
@@ -375,7 +382,7 @@ 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;
+ unsigned int bytes = 0;
struct req_iterator iter;
struct bio_vec bv;

@@ -398,7 +405,7 @@ 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,
+ bvec_split_segs(rq->q, &bv, &nr_phys_segs, &bytes,
UINT_MAX, UINT_MAX);
return nr_phys_segs;
}
--
2.30.2