linux-kernel - Re: [PATCH 3/5] mm: add static huge zero folio

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Message-ID: <76e26491-e91a-49fc-9a5b-eb6d840a066e@redhat.com>
Date: Wed, 6 Aug 2025 14:48:38 +0200
From: David Hildenbrand <david@...hat.com>
To: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 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,
 linux-mm@...ck.org, willy@...radead.org, x86@...nel.org,
 linux-block@...r.kernel.org, Ritesh Harjani <ritesh.list@...il.com>,
 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 3/5] mm: add static huge zero folio

On 06.08.25 14:43, Pankaj Raghav (Samsung) wrote:
> On Wed, Aug 06, 2025 at 02:36:51PM +0200, David Hildenbrand wrote:
>> On 06.08.25 14:28, Pankaj Raghav (Samsung) wrote:
>>> On Wed, Aug 06, 2025 at 02:24:28PM +0200, David Hildenbrand wrote:
>>>> On 06.08.25 14:18, Pankaj Raghav (Samsung) wrote:
>>>>>> We could go one step further and special case in mm_get_huge_zero_folio() +
>>>>>> mm_put_huge_zero_folio() on CONFIG_STATIC_HUGE_ZERO_FOLIO.
>>>>>>
>>>>>
>>>>> Hmm, but we could have also failed to allocate even though the option
>>>>> was enabled.
>>>>
>>>> Then we return huge_zero_folio, which is NULL?
>>>>
>>>> Or what are you concerned about?
>>>
>>> But don't we want to keep the "dynamic" allocation part be present even
>>> though we failed to allocate it statically in the shrinker_init?
>>>
>>> Mainly so that the existing users of mm_get_huge_zero_folio() are not affected by
>>> these changes.
>>
>> I would just keep it simple and say that if we fail the early allocation
>> (which will be extremely unlikely that early during boot!), just don't ever
>> try to reallocate, even not when we could through mm_get_huge_zero_folio().
>>
>> That sounds as simple as it gets. Again, failing to allocate that early and
>> then succeeding to allocate later is a fairly unlikely scenario.
> 
> Ok. I will also document this as a comment just so that people are aware of
> this behaviour.
> 
> Thanks a lot David for the comments and feedback!

Sure, as always, feel free to object if you think I am talking nonsense :)

-- 
Cheers,

David / dhildenb