From ee623c892aa59003fca173de0041abc2ccc2c72d Mon Sep 17 00:00:00 2001 From: Ming Lei Date: Wed, 31 Dec 2025 11:00:55 +0800 Subject: 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 Reviewed-by: Nitesh Shetty Signed-off-by: Jens Axboe --- include/linux/blk_types.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'include') 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; }; -- cgit v1.2.3