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

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Message-ID: <9a657c84-99fe-41ba-88ca-097acab4b96b@redhat.com>
Date: Wed, 6 Aug 2025 14:36:51 +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 14:28, 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.

-- 
Cheers,

David / dhildenb