Re: [PATCH 2/2] block: remove the bi_inline_vecs variable sized array from struct bio

[Yu Kuai <yukuai1@xxxxxxxxxxxxxxx>]

Hi,

在 2025/09/09 16:55, John Garry 写道:
> On 09/09/2025 09:40, Yu Kuai wrote:
> > 在 2025/09/09 16:16, John Garry 写道:
> > > > diff --git a/drivers/md/bcache/movinggc.c 
> > > > b/drivers/md/bcache/movinggc.c
> > > > index 4fc80c6d5b31..73918e55bf04 100644
> > > > --- a/drivers/md/bcache/movinggc.c
> > > > +++ b/drivers/md/bcache/movinggc.c
> > > > @@ -145,9 +145,9 @@ static void read_moving(struct cache_set *c)
> > > >               continue;
> > > >           }
> > > > -        io = kzalloc(struct_size(io, bio.bio.bi_inline_vecs,
> > > > -                     DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS)),
> > > > -                 GFP_KERNEL);
> > > > +        io = kzalloc(sizeof(*io) + sizeof(struct bio_vec) *
> > > > +                DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS),
> > > > +                GFP_KERNEL);
> > >
> > > this seems a common pattern, so maybe another helper (which could be 
> > > used by bio_kmalloc)? I am not advocating it, but just putting the 
> > > idea out there... too many helpers makes it messy IMHO
> >
> > Not sure how to do this, do you mean a marco to pass in the base
> > structure type, nr_vecs and the gfp_mask?
>
> something like the following (which I think is messy and an imprecise 
> API, so again I am not advocating it):
>
> struct bio *bio_kmalloc(unsigned short nr_vecs, gfp_t gfp_mask)
> {
>      return kmalloc(sizeof(struct bio) + nr_vecs * sizeof(struct bio_vec),
> gfp_mask);
> }
>
> struct bio *bio_kmalloc_inline(unsigned short nr_vecs, gfp_t gfp_mask)
> {
>      if (nr_vecs > BIO_MAX_INLINE_VECS)
>          return NULL;
>      return bio_kmalloc(nr_vecs, gfp_mask);
> }
However, the caller is allocating the base structure that bio is
embedded, the above helper to return bio is still not common.

Perhaps this patch is better anyway.

Thanks,
Kuai
> .