linux-kernel - Re: [PATCH v1 2/4] mm: smaller folio_pte

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Message-ID: <753a8900-d9ff-436c-8758-17d363967b30@lucifer.local>
Date: Wed, 2 Jul 2025 09:51:30 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: David Hildenbrand <david@...hat.com>
Cc: Oscar Salvador <osalvador@...e.de>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
        Mike Rapoport <rppt@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
        Zi Yan <ziy@...dia.com>, Matthew Brost <matthew.brost@...el.com>,
        Joshua Hahn <joshua.hahnjy@...il.com>, Rakie Kim <rakie.kim@...com>,
        Byungchul Park <byungchul@...com>, Gregory Price <gourry@...rry.net>,
        Ying Huang <ying.huang@...ux.alibaba.com>,
        Alistair Popple <apopple@...dia.com>, Pedro Falcato <pfalcato@...e.de>,
        Rik van Riel <riel@...riel.com>, Harry Yoo <harry.yoo@...cle.com>
Subject: Re: [PATCH v1 2/4] mm: smaller folio_pte_batch() improvements

On Wed, Jul 02, 2025 at 10:48:20AM +0200, David Hildenbrand wrote:
> On 02.07.25 10:42, Oscar Salvador wrote:
> > On Fri, Jun 27, 2025 at 01:55:08PM +0200, David Hildenbrand wrote:
> > > Let's clean up a bit:
> > >
> > > (1) No need for start_ptep vs. ptep anymore, we can simply use ptep
> > >
> > > (2) Let's switch to "unsigned int" for everything
> > >
> > > (3) We can simplify the code by leaving the pte unchanged after the
> > >      pte_same() check.
> > >
> > > (4) Clarify that we should never exceed a single VMA; it indicates a
> > >      problem in the caller.
> > >
> > > No functional change intended.
> > >
> > > Signed-off-by: David Hildenbrand <david@...hat.com>
> >
> > Hi David :-),
> >
> > I have to confess that I fell in the same trap as Lorenzo wrt.
> > __pte_batch_clear_ignored changing the pte value.
> > So I'm not sure if it would be nice to place a little comment in
> > __pte_batch_clear_ignored claryfing that pte's value remains unchanged ?
>
> I mean, that's how all our pte modification functions work, really? :)
>
> Thanks!

I mean, it might be that me and Oscar are similarly 'challenged' in this
respect :P (high 5 Oscar!) but I think the issue here is that it's sort of
a compounded use, and in fact some functions do modify stuff, which is why
we end up with all the ptep ptent etc. fun.

Up to you re: comment, but I think maybe in cases where it's a reallly
compounded set of stuff it's potentially useful.

But obviously we still do do this all over the place elsewhere with no
comment...

>
> --
> Cheers,
>
> David / dhildenb
>
>