linux-kernel - Re: [RFC PATCH v2 00/20] Reimplement huge pages without hugepd on powerpc (8xx, e500, book3s/64)

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Date: Fri, 24 May 2024 14:46:58 +1000
From: Michael Ellerman <mpe@...erman.id.au>
To: Peter Xu <peterx@...hat.com>, Christophe Leroy
 <christophe.leroy@...roup.eu>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Jason Gunthorpe
 <jgg@...dia.com>, Oscar Salvador <osalvador@...e.de>, Nicholas Piggin
 <npiggin@...il.com>, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 linuxppc-dev@...ts.ozlabs.org
Subject: Re: [RFC PATCH v2 00/20] Reimplement huge pages without hugepd on
 powerpc (8xx, e500, book3s/64)

Hi Peter,

Peter Xu <peterx@...hat.com> writes:
> On Fri, May 17, 2024 at 08:59:54PM +0200, Christophe Leroy wrote:
>> This is the continuation of the RFC v1 series "Reimplement huge pages
>> without hugepd on powerpc 8xx". It now get rid of hugepd completely
>> after handling also e500 and book3s/64
>> 
>> Unlike most architectures, powerpc 8xx HW requires a two-level
>> pagetable topology for all page sizes. So a leaf PMD-contig approach
>> is not feasible as such.
...
>
> Great to see this series, thanks again Christophe.
>
> I requested for help on the lsfmm hugetlb unification session, but
> unfortunately I don't think there were Power people around.. I'd like to
> request help from Power developers again here on the list: it will be very
> appreciated if you can help have a look at this series.

Christophe is a powerpc developer :)

I'll help where I can, but I don't know the hugepd code that well, I've
never really worked on it before. Nick will hopefully also be able to
help, he at least knows mm better than me, but he also has other work.

Hopefully we can make this series work, and replace hugepd. But if we
can't make that work then there is the possibility of just dropping
support for 16M/16G pages with HPT/4K pages.

> It's a direct dependent work to the hugetlb refactoring that we'll be
> working on, while it looks like the hugetlb refactoring is something the
> community as a whole would like to see in the near future.
>
> We don't want to add more Power-only CONFIG_ARCH_HAS_HUGEPD checks for
> hugetlb in any new code.

Yes I understand.

cheers