Re: [RFC PATCH 2/3] mm: drop stale folio_ref_count()==1 check in do_swap_page reuse logic

[Kairui Song]

On Thu, Jun 11, 2026 at 6:52 PM Barry Song (Xiaomi) <baohua@xxxxxxxxxx> 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/
> 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 487a34377a7b..ce8ef27e7a54 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
> -        * 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) {
>                 if ((vma->vm_flags & VM_WRITE) && !userfaultfd_pte_wp(vma, pte) &&
>                     !pte_needs_soft_dirty_wp(vma, pte)) {
>                         pte = pte_mkwrite(pte, vma);

Reviewed-by: Kairui Song <kasong@xxxxxxxxxxx>