Re: [PATCH v2 2/4] mm: drop stale folio_ref_count()==1 check in do_swap_page reuse logic

[Barry Song]

On Wed, Jun 24, 2026 at 11:08 PM David Hildenbrand (Arm)
<david@xxxxxxxxxx> wrote:
>
> On 6/24/26 01:16, Barry Song (Xiaomi) wrote:
> > The "we just allocated them without exposing them to the swapcache"
> > case no longer exists, as Kairui has routed synchronous I/O through
> > the swapcache as well in his series "unify swapin use swap cache and
> > cleanup flags"[1]. As a result, folio_ref_count() should never be 1
> > in this path, since at least two references are held (base ref plus
> > swapcache). Remove the folio_ref_count()==1 check and update the
> > comment accordingly.
> >
> > [1] https://lore.kernel.org/all/20251220-swap-table-p2-v5-0-8862a265a033@xxxxxxxxxxx/
> >
> > Acked-by: Usama Arif <usama.arif@xxxxxxxxx>
> > Reviewed-by: Kairui Song <kasong@xxxxxxxxxxx>
> > Reviewed-by: Baoquan He <baoquan.he@xxxxxxxxx>
> > Acked-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>
> > Signed-off-by: Barry Song (Xiaomi) <baohua@xxxxxxxxxx>
> > ---
> >  mm/memory.c | 7 ++-----
> >  1 file changed, 2 insertions(+), 5 deletions(-)
> >
> > diff --git a/mm/memory.c b/mm/memory.c
> > index f6848f4234a6..abd0adcf65f0 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -5049,12 +5049,9 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
> >
> >       /*
> >        * Same logic as in do_wp_page(); however, optimize for pages that are
>
> s/Same/Similar/ ?

will change to similar in v3.

>
> > -      * certainly not shared either because we just allocated them without
> > -      * exposing them to the swapcache or because the swap entry indicates
> > -      * exclusivity.
> > +      * certainly not because the swap entry indicates exclusivity.
> >        */
> > -     if (!folio_test_ksm(folio) &&
> > -         (exclusive || folio_ref_count(folio) == 1)) {
> > +     if (!folio_test_ksm(folio) && exclusive) {
>
> Hmm, but KSM folios should never have "exclusive" set. So I think you can drop
> that as well (was only relevant with folio_ref_count==1 check IIRC).

right. will drop !folio_test_ksm(folio) in v3.

Best Regards
Barry