Re: [PATCH] mm/thp: expose deferred split folio memory usage in meminfo

[Lorenzo Stoakes (ARM)]

On Fri, Jul 17, 2026 at 10:37:21AM +0200, David Hildenbrand (Arm) wrote:
> On 7/17/26 08:30, Ye Liu wrote:
> > From: Ye Liu <liuye@xxxxxxxxxx>
> >
> > Folios on the deferred split list hold physical memory that is
> > invisible in meminfo. When a THP becomes partially mapped, the
> > unmapped pages are removed from AnonPages but remain physically
> > allocated until the shrinker splits the folio. This creates a
> > memory accounting gap where used memory cannot be attributed to
> > any meminfo field.
> >
> > Add NR_DEFERRED_SPLIT_PAGES to track the total memory consumed by
> > folios currently on the deferred_split_lru, updated via
> > mod_node_page_state() at all enqueue/dequeue points. The new field
> > DeferredSplitPages is visible in /proc/meminfo, /proc/vmstat, and
> > per-node /sys/devices/system/node/node*/meminfo.
> >
>
> Oh no.
>
> This is really exposing a current implementation detail where we have this
> information easily available in a way that we will not be able to change that
> implementation later.

Yes, also this :) agree entirely.

>
> --
> Cheers,
>
> David

Thanks, Lorenzo