Re: [PATCH] memcg: sink mem_cgroup_uncharge_folios() into free_unref_folios()

[Ridong Chen]

On 8/27/2026 10:52 PM, Johannes Weiner wrote:
> On Thu, Aug 27, 2026 at 11:05:16AM +0800, Ridong Chen wrote:
> > From: Ridong Chen <chenridong@xxxxxxxxxx>
> >
> > Every caller of free_unref_folios() invokes mem_cgroup_uncharge_folios()
> > on the same batch immediately beforehand.  This pattern is duplicated
> > across shrink_folio_list(), move_folios_to_lru(), folio_batch_move_lru()
> > and folios_put_refs().
> >
> > Move the uncharge into free_unref_folios() itself so the batch is
> > uncharged in one place before the folios are freed.  This removes the
> > repeated boilerplate at every call site and makes it impossible to free
> > a batch without uncharging it first.  No functional change intended.
>
> Hm, IMO this is confusing. You're making uncharging an included
> service in a subset of the page allocator freeing API. Batch freeing
> uncharges, but single page freeing does not.
>
> I don't think saving 7 lines is worth that API caveat.

Thanks Johannes.

I thought this could improve cohesion, since we have to uncharge the batch when 
freeing unreferenced folios. However, I didn't consider the symmetry with single 
folio freeing.

I'll just drop the patch if it's causing confusion.

--
Best regards
Ridong