linux-kernel - Re: [PATCH v2 1/5] mm: move huge_zero_page declaration from huge

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Message-ID: <da5aea8a-bae5-4cd5-83a1-94cfcb61a29f@redhat.com>
Date: Wed, 16 Jul 2025 17:24:15 +0200
From: David Hildenbrand <david@...hat.com>
To: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Suren Baghdasaryan <surenb@...gle.com>,
 Ryan Roberts <ryan.roberts@....com>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>, Borislav Petkov <bp@...en8.de>,
 Ingo Molnar <mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>,
 Vlastimil Babka <vbabka@...e.cz>, Zi Yan <ziy@...dia.com>,
 Mike Rapoport <rppt@...nel.org>, Dave Hansen <dave.hansen@...ux.intel.com>,
 Michal Hocko <mhocko@...e.com>, Andrew Morton <akpm@...ux-foundation.org>,
 Thomas Gleixner <tglx@...utronix.de>, Nico Pache <npache@...hat.com>,
 Dev Jain <dev.jain@....com>, "Liam R . Howlett" <Liam.Howlett@...cle.com>,
 Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
 willy@...radead.org, linux-mm@...ck.org, x86@...nel.org,
 linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 "Darrick J . Wong" <djwong@...nel.org>, mcgrof@...nel.org,
 gost.dev@...sung.com, hch@....de, Pankaj Raghav <p.raghav@...sung.com>
Subject: Re: [PATCH v2 1/5] mm: move huge_zero_page declaration from huge_mm.h
 to mm.h

On 16.07.25 09:47, Pankaj Raghav (Samsung) wrote:
> On Tue, Jul 15, 2025 at 03:08:40PM +0100, Lorenzo Stoakes wrote:
>> On Mon, Jul 07, 2025 at 04:23:15PM +0200, Pankaj Raghav (Samsung) wrote:
>>> From: Pankaj Raghav <p.raghav@...sung.com>
>>>
>>> Move the declaration associated with huge_zero_page from huge_mm.h to
>>> mm.h. This patch is in preparation for adding static PMD zero page as we
>>> will be reusing some of the huge_zero_page infrastructure.
>>
>> Hmm this is really iffy.
>>
>> The whole purpose of huge_mm.h is to handle huge page stuff, and now you're
>> moving it to a general header... not a fan of this - now we have _some_
>> huge stuff in mm.h and some stuff here.
>>
>> Yes this might be something we screwed up already, but that's not a recent
>> to perpetuate mistakes.
>>
>> Surely you don't _need_ to do this and this is a question of fixing up
>> header includes right?
>>
>> Or is them some horrible cyclical header issue here?
>>
>> Also your commit message doesn't give any reason as to why you _need_ to do
>> this also. For something like this where you're doing something that at
>> face value seems to contradict the purpose of these headers, you need to
>> explain why.
>>
> 
> In one of the earlier versions, David asked me to experiment by moving some of these
> declarations to mm.h and see how it looks. Mainly because, as you
> guessed it later, we can use it without THP being enabled.

I assume, in the future, most setups we care about (-> performance) will 
have THP compiled in. So likely we can defer moving it until it's really 
required.

-- 
Cheers,

David / dhildenb