Re: [PATCH v3 2/4] mm: drop stale folio_ref_count()==1 check in do_swap_page reuse logic

[Barry Song]

On Thu, Jul 2, 2026 at 4:14 PM David Hildenbrand (Arm) <david@xxxxxxxxxx> wrote:
>
> On 7/2/26 01:59, 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.
>
> Sashiko points out two minor things (one flagged as medium, lol, sure sure).
>
> Here, you can clarify that folio_ref_count()==1 is true for freshly allocated
> pages (due to the KSM check) in which case exclusive=true already.

Hi Andrew,

I saw that you've queued this in mm-new. Thanks very much for that!

Would you mind adding the following sentences to the end of the changelog?

The ksm_might_need_to_copy() check may allocate a fresh folio with
folio_ref_count() == 1. Along that path, exclusive has already been
set to true, so the folio can still be reused correctly.

Best Regards
Barry