diff options
| author | Ming Lei <ming.lei@redhat.com> | 2025-12-31 11:00:55 +0800 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2026-01-07 08:06:33 -0700 |
| commit | ee623c892aa59003fca173de0041abc2ccc2c72d (patch) | |
| tree | af9f4c724f1a723f04ff14ccc238891107bf45c3 | |
| parent | 69d26698e4fd44935510553809007151b2fe4db5 (diff) | |
block: use bvec iterator helper for bio_may_need_split()
bio_may_need_split() uses bi_vcnt to determine if a bio has a single
segment, but bi_vcnt is unreliable for cloned bios. Cloned bios share
the parent's bi_io_vec array but iterate over a subset via bi_iter,
so bi_vcnt may not reflect the actual segment count being iterated.
Replace the bi_vcnt check with bvec iterator access via
__bvec_iter_bvec(), comparing bi_iter.bi_size against the current
bvec's length. This correctly handles both cloned and non-cloned bios.
Move bi_io_vec into the first cache line adjacent to bi_iter. This is
a sensible layout since bi_io_vec and bi_iter are commonly accessed
together throughout the block layer - every bvec iteration requires
both fields. This displaces bi_end_io to the second cache line, which
is acceptable since bi_end_io and bi_private are always fetched
together in bio_endio() anyway.
The struct layout change requires bio_reset() to preserve and restore
bi_io_vec across the memset, since it now falls within BIO_RESET_BYTES.
Nitesh verified that this patch doesn't regress NVMe 512-byte IO perf [1].
Link: https://lore.kernel.org/linux-block/20251220081607.tvnrltcngl3cc2fh@green245.gost/ [1]
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Nitesh Shetty <nj.shetty@samsung.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
| -rw-r--r-- | block/bio.c | 3 | ||||
| -rw-r--r-- | block/blk.h | 12 | ||||
| -rw-r--r-- | include/linux/blk_types.h | 4 |
3 files changed, 14 insertions, 5 deletions
diff --git a/block/bio.c b/block/bio.c index e726c0e280a8..0e936288034e 100644 --- a/block/bio.c +++ b/block/bio.c @@ -301,9 +301,12 @@ EXPORT_SYMBOL(bio_init); */ void bio_reset(struct bio *bio, struct block_device *bdev, blk_opf_t opf) { + struct bio_vec *bv = bio->bi_io_vec; + bio_uninit(bio); memset(bio, 0, BIO_RESET_BYTES); atomic_set(&bio->__bi_remaining, 1); + bio->bi_io_vec = bv; bio->bi_bdev = bdev; if (bio->bi_bdev) bio_associate_blkg(bio); diff --git a/block/blk.h b/block/blk.h index e4c433f62dfc..98f4dfd4ec75 100644 --- a/block/blk.h +++ b/block/blk.h @@ -371,12 +371,18 @@ struct bio *bio_split_zone_append(struct bio *bio, static inline bool bio_may_need_split(struct bio *bio, const struct queue_limits *lim) { + const struct bio_vec *bv; + if (lim->chunk_sectors) return true; - if (bio->bi_vcnt != 1) + + if (!bio->bi_io_vec) + return true; + + bv = __bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter); + if (bio->bi_iter.bi_size > bv->bv_len) return true; - return bio->bi_io_vec->bv_len + bio->bi_io_vec->bv_offset > - lim->max_fast_segment_size; + return bv->bv_len + bv->bv_offset > lim->max_fast_segment_size; } /** diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h index 5dc061d318a4..19a888a2f104 100644 --- a/include/linux/blk_types.h +++ b/include/linux/blk_types.h @@ -232,6 +232,8 @@ struct bio { atomic_t __bi_remaining; + /* The actual vec list, preserved by bio_reset() */ + struct bio_vec *bi_io_vec; struct bvec_iter bi_iter; union { @@ -275,8 +277,6 @@ struct bio { atomic_t __bi_cnt; /* pin count */ - struct bio_vec *bi_io_vec; /* the actual vec list */ - struct bio_set *bi_pool; }; |