Re: [PATCH] block: set bi_vcnt when cloning bio

[John Garry]

On 18/02/2025 22:21, Bart Van Assche wrote:
> On 2/18/25 9:12 AM, John Garry wrote:
> > On 18/02/2025 11:40, Andreas Hindborg wrote:
> > > But I am genuinely curious if there is a reason for not setting
> > > `bi_vcnt` during a clone.
> >
> > I think that it came from commit 59d276fe0 (with the addition of 
> > bio_clone_fast()), where we assume that the cloned bio is not having 
> > the bio_vec touched and so does not need to know bi_vcnt (or 
> > bi_max_vecs). And it is inefficient to needlessly set bi_vcnt then.
>
> Hmm ... I prefer paying the very small performance hit caused by copying
> bi_vcnt rather than having to deal with the inconsistency caused by not
> copying that data structure member.

From my experience, setting anything which is not strictly necessary in 
the fastpath code is generally not wanted.

Thanks,
John