Re: [PATCH v2 00/16] mm: remove is_swap_[pte, pmd]() + non-swap entries, introduce leaf entries

Lorenzo Stoakes
2025-11-11T06:57:37Z

Andrew - in light of the below can we put this back in mm-unstable please?
I'd like the bots to be on this and obviously hoping for inclusion in 6.19
:)

On Mon, Nov 10, 2025 at 08:07:34PM -0800, Hugh Dickins wrote:
> On Mon, 10 Nov 2025, Andrew Morton wrote:
> > On Mon, 10 Nov 2025 15:38:55 -0800 (PST) Hugh Dickins <hughd@google.com> wrote:
> >
> > > > I'm sorry but this is not a reasonable request. I am being as empathetic and
> > > > kind as I can be here, but this series is proceeding without arbitrary delay.
> > > >
> > > > I will do everything I can to accommodate any concerns or issues you may have
> > > > here _within reason_ :)
> > >
> > > But Lorenzo, have you even tested your series properly yet, with
> > > swapping and folio migration and huge pages and tmpfs under load?
> > > Please do.

I did a whole bunch of testing, of course it's never enough in practice :)

> > >
> > > I haven't had time to bisect yet, maybe there's nothing more needed
> > > than a one-liner fix somewhere; but from my experience it is not yet
> > > ready for inclusion in mm and next - it stops testing other folks' work.
> > >
> > > I haven't tried today's v3, but from the cover letter of differences,
> > > it didn't look like much of importance is fixed since v2: which
> > > (after a profusion of "Bad swap offet entry 3ffffffffffff" messages,
> > > not seen with v1, and probably not really serious) soon hits an Oops
> > > or a BUG or something (as v1 did) - I don't have any logs or notes
> > > to give yet, just forewarning before pursuing later in the day.
> > >
> > > If you think v3 has fixed real crashes under load, please say so:
> > > otherwise, I doubt it's worth Andrew hurrying to replace v2 by v3.
> >
> > Oh. Thanks. I'll move the v3 series into mm-new for now.
>
> Lorenzo, I can happily apologize: the v3 series in mm-everything-
> 2025-11-11-01-20 is a big improvement over v2 and v1, it is showing
> none of the bad behaviours I saw with those. I've not searched or
> compared for what actually fixed those symptoms (though have now
> spotted mails from Shivank and Kairui regarding 3ffffffffffff),
> I'm content now to move on to unrelated work...

Thanks yeah there were a couple oversights, one due to shenanigans around
how zero swap entries are represented, and another due to some frankly
insane code in the swap implementation.

I feel this change is very necessary for us to a. have clearer
understanding of this logic, and b. to be able to build upon it sensibly in
future.

This change is selfish also in that I intend to add huge guard markers in
future, and a previous attempt building upon the mass of confusion and
horror that was 'non-swap swap' felt borderline unworkable :)

>
> Thanks,
> Hugh

Cheers, Lorenzo