Re: [PATCH V2] blk-mq: add blk_rq_nr_bvec() helper

[Keith Busch <kbusch@kernel.org>]

On Tue, Nov 11, 2025 at 03:22:52PM -0800, Chaitanya Kulkarni wrote:
> This patch also provides a clear API to avoid any potential misuse of
> blk_nr_phys_segments() for calculating the bvecs since, one bvec can
> have more than one segments and use of blk_nr_phys_segments() can
> lead to extra memory allocation :-

Perhaps blk_nr_phys_segments is misnamed as it represents device
segments, not physical host memory segments. Instead of rewalking to
calculate physical segments, maybe just introduce a new field into the
request so that we can save both the physical and device segments to
avoid having to repeatedly rewalk the same list. There is an ongoing
effort to avoid such repeated work.