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

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Message-ID: <ca35da97-13d1-49f1-95b0-b8b9c8a7f540@redhat.com>
Date: Tue, 5 Aug 2025 14:10:39 +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 05.08.25 13:40, Pankaj Raghav (Samsung) wrote:
> Thanks a lot Lorenzo and David for the feedback and quick iteration on
> the patchset. I really like the number of lines of code has been
> steadily reducing since the first version :)
> 
> I will fold the changes in the next series.
> 
> <snip>
>>>> @@ -866,9 +866,14 @@ static int __init thp_shrinker_init(void)
>>>>    	huge_zero_folio_shrinker->scan_objects = shrink_huge_zero_folio_scan;
>>>>    	shrinker_register(huge_zero_folio_shrinker);
>>>> -	deferred_split_shrinker->count_objects = deferred_split_count;
>>>> -	deferred_split_shrinker->scan_objects = deferred_split_scan;
>>>> -	shrinker_register(deferred_split_shrinker);
>>>> +	if (IS_ENABLED(CONFIG_STATIC_HUGE_ZERO_FOLIO)) {
>>>> +		if (!get_huge_zero_folio())
>>>> +			pr_warn("Allocating static huge zero folio failed\n");
>>>> +	} else {
>>>> +		deferred_split_shrinker->count_objects = deferred_split_count;
>>>> +		deferred_split_shrinker->scan_objects = deferred_split_scan;
>>>> +		shrinker_register(deferred_split_shrinker);
>>>> +	}
>>>>    	return 0;
>>>>    }
>>>> --
>>>> 2.50.1
>>>>
>>>>
>>>> Now, one thing I do not like is that we have "ARCH_WANTS_STATIC_HUGE_ZERO_FOLIO" but
>>>> then have a user-selectable option.
>>>>
>>>> Should we just get rid of ARCH_WANTS_STATIC_HUGE_ZERO_FOLIO?
>>>
> 
> One of the early feedbacks from Lorenzo was that there might be some
> architectures that has PMD size > 2M might enable this by mistake. So
> the ARCH_WANTS_STATIC_HUGE_ZERO_FOLIO was introduced as an extra
> precaution apart from user selectable CONFIG_STATIC_HUGE_ZERO_FOLIO.

People will find creative ways to mis-configure their system no matter 
what you try :)

So I think best we can do is document it carefully.

-- 
Cheers,

David / dhildenb