Re: [PATCH v2] mm/shmem: fix THP allocation and fallback loop

[Barry Song <21cnbao@gmail.com>]

On Thu, Oct 23, 2025 at 6:58 PM Kairui Song <ryncsn@gmail.com> wrote:
>
> On Thu, Oct 23, 2025 at 1:51 PM Barry Song <21cnbao@gmail.com> wrote:
> > > diff --git a/mm/shmem.c b/mm/shmem.c
> > > index b50ce7dbc84a..7559773ebb30 100644
> > > --- a/mm/shmem.c
> > > +++ b/mm/shmem.c
> > > @@ -1895,10 +1895,11 @@ static struct folio *shmem_alloc_and_add_folio(struct vm_fault *vmf,
> > >                 order = highest_order(suitable_orders);
> > >                 while (suitable_orders) {
> > >                         pages = 1UL << order;
> > > -                       index = round_down(index, pages);
> > > -                       folio = shmem_alloc_folio(gfp, order, info, index);
> > > -                       if (folio)
> > > +                       folio = shmem_alloc_folio(gfp, order, info, round_down(index, pages));
> > > +                       if (folio) {
> > > +                               index = round_down(index, pages);
> > >                                 goto allocated;
> > > +                       }
> >
> > Could this be a temporary variable to store round_down(index, pages)?
>
> Right we can do that, but the generated code should be the same, the
> compiler is smart enough, I just checked the generated code with gcc /
> clang.
>
> Do you think the code will be cleaner with a temporary variable? I can
> send a V3 if anyone suggests, it's really a trivial change.

Personally, I think a temporary variable makes the code cleaner, but I don’t
have any strong preference.

The fix looks correct to me.

Thanks
Barry