Re: [PATCH] Revert "ptdesc: remove references to folios from __pagetable_ctor() and pagetable_dtor()"

[Shakeel Butt]

+memcg maintainers

On Wed, Feb 25, 2026 at 05:08:28PM +0100, David Hildenbrand (Arm) wrote:
> On 2/25/26 17:03, Matthew Wilcox wrote:
> > On Tue, Feb 24, 2026 at 04:24:34PM -0800, Axel Rasmussen wrote:
> >> This change swapped out mod_node_page_state for lruvec_stat_add_folio.
> >> But, these two APIs are not interchangeable: the lruvec version also
> >> increments memcg stats, in addition to "global" pgdat stats.
> >>
> >> So after this change, the "pagetables" memcg stat in memory.stat always
> >> yields "0", which is a userspace visible regression.
> >>
> >> I tried to look for a refactor where we add a variant of
> >> lruvec_stat_mod_folio which takes a pgdat and a memcg instead of a
> >> folio, to try to adhere to the spirit of the original patch. But at the
> >> end of the day this just means we have to call
> >> folio_memcg(ptdesc_folio(ptdesc)) anyway, which doesn't really
> >> accomplish much.
> > 
> > Thank you!  I hadn't been able to get a straight answer on this before.
> > 
> > You're right that there's no good function to call, but that just means
> > we need to make one.  The principle here is that (eventually) different
> > memdescs don't need to know about each other.  Obviously we're not there
> > yet, but we can start disentangling them by not casting ptdescs back to
> > folios (even though they're created that way).
> > 
> > Here's three patches smooshed together; I have them separately and I'll
> > post them soon.
> 
> Should we just apply + backport the revert for now and re-do it based on
> the revert?

Yes please.