Re: [PATCH 14/22] mm: set page table page type when allocated

[Kevin Brodsky]

On 14/07/2026 17:16, Vishal Moola wrote:
> On Tue, Jul 14, 2026 at 03:04:03PM +0100, Kevin Brodsky wrote:
>> As a step towards removing pagetable ctor/dtor calls for kernel
>> mm's, move the page type updates from the ctor/dtor to
>> pagetable_{alloc,free}.
> Thanks for doing this patchset.

Thanks for suggesting it :) It's turning out to be quite a bit more
involved than I expected though! (There are multiple cases where we call
the ctor/dtor without using pagetable_{alloc,free}, see my reply to the
cover letter.)

> We should switch over from __folio_set_pgtable() to __SetPagePgtable()
> in this patch. Ptdescs and folios should be treated as distinctly
> independent of each other.

I sure remember the previous discussion, but my reading of your comments
[1] is that we cannot really change this as long as pagetable_alloc()
can be called with order > 0, right? Multiple archs still rely on that.

> Eventually, we want to replace the memcg accounting as well, but
> there's no existing API for that right now. Lets leave that as is for
> now; this patchset is big enough already ;)

Yep, looks like there was an attempt to improve this but it had to be
reverted [2].

- Kevin

[1] https://lore.kernel.org/all/aha321ndGSdReBJR@fedora/
[2]
https://lore.kernel.org/all/20260225002434.2953895-1-axelrasmussen@xxxxxxxxxx/