Re: [PATCH V2 0/3] block: avoid to use bi_vcnt in bio_may_need_split()

[Ming Lei <ming.lei@redhat.com>]

On Wed, Dec 31, 2025 at 11:00:54AM +0800, Ming Lei wrote:
> This series cleans up bio handling to use bi_iter consistently for both
> cloned and non-cloned bios, removing the reliance on bi_vcnt which is
> only meaningful for non-cloned bios.
> 
> Currently, bio_may_need_split() uses bi_vcnt to check if a bio has a
> single segment. While this works, it's inconsistent with how cloned bios
> operate - they use bi_iter for iteration, not bi_vcnt. This inconsistency
> led to io_uring needing to recalculate iov_iter.nr_segs to ensure bi_vcnt
> gets a correct value when copied.
> 
> This series unifies the approach:
> 
> 1. Make bio_may_need_split() use bi_iter instead of bi_vcnt. This handles
>    both cloned and non-cloned bios in a consistent way. Also move bi_io_vec
>    adjacent to bi_iter in struct bio since they're commonly accessed
>    together.
> 
> 2. Stop copying iov_iter.nr_segs to bi_vcnt in bio_iov_bvec_set(), since
>    cloned bios should rely on bi_iter, not bi_vcnt.
> 
> 3. Remove the nr_segs recalculation in io_uring, which was only needed
>    to provide an accurate bi_vcnt value.
> 
> Nitesh verified no performance regression on NVMe 512-byte fio/t/io_uring
> workloads.
> 
> V2:
> 	- improve bio layout by putting bi_iter and bi_io_vec together
> 	- improve commit log

Hello Guys,

Ping...


Thanks,
Ming