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

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

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

Ming Lei (3):
  block: use bvec iterator helper for bio_may_need_split()
  block: don't initialize bi_vcnt for cloned bio in bio_iov_bvec_set()
  io_uring: remove nr_segs recalculation in io_import_kbuf()

 block/bio.c               |  5 ++++-
 block/blk.h               | 12 +++++++++---
 include/linux/blk_types.h |  4 ++--
 io_uring/rsrc.c           | 11 -----------
 4 files changed, 15 insertions(+), 17 deletions(-)

-- 
2.47.0