linux-kernel - Re: [PATCH 2/3] mm: Add generic helper to hint a large folio

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Message-ID: <900a8898-0666-4639-9a0a-7e602eed275f@redhat.com>
Date: Fri, 9 May 2025 11:16:07 +0200
From: David Hildenbrand <david@...hat.com>
To: Dev Jain <dev.jain@....com>, akpm@...ux-foundation.org
Cc: Liam.Howlett@...cle.com, lorenzo.stoakes@...cle.com, vbabka@...e.cz,
 jannh@...gle.com, pfalcato@...e.de, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, peterx@...hat.com, ryan.roberts@....com,
 mingo@...nel.org, libang.li@...group.com, maobibo@...ngson.cn,
 zhengqi.arch@...edance.com, baohua@...nel.org, anshuman.khandual@....com,
 willy@...radead.org, ioworker0@...il.com, yang@...amperecomputing.com
Subject: Re: [PATCH 2/3] mm: Add generic helper to hint a large folio

On 09.05.25 07:25, Dev Jain wrote:
> 
> 
> On 08/05/25 4:25 pm, David Hildenbrand wrote:
>>
>>>> (2) Do we really need "must be part of the same folio", or could be just
>>>> batch over present
>>>> ptes that map consecutive PFNs? In that case, a helper that avoids
>>>> folio_pte_batch() completely
>>>> might be better.
>>>>
>>> I am not sure I get you here. folio_pte_batch() seems to be the simplest
>>> thing we can do as being done around in the code elsewhere, I am not
>>> aware of any alternate.
>>
>> If we don't need the folio, then we can have a batching function that
>> doesn't require the folio.
>>
>> Likely, we could even factor that (non-folio batching) out from
>> folio_pte_batch().
>> The recent fix [1] might make that easier. See below.
>>
>>
>> So my question is: is something relying on all of these PTEs to point at
>> the same folio?
> 
> Hmm...get_and_clear_full_ptes, as you say in another mail, will require
> that...
> 
>>
>> [1] https://lkml.kernel.org/r/20250502215019.822-2-arkamar@atlas.cz
>>
>>
>> Something like this: (would need kerneldoc, probably remove "addr"
>> parameter from folio_pte_batch(),
>> and look into other related cleanups as discussed with Andrew)
> 
> I like this refactoring! Can you tell the commit hash on which you make
> the patch, I cannot apply it.

Oh, it was just on top of my private version of [1]. It should now be in 
mm-new (or mm-unstable, did not check).

But as raised in my other mail, get_and_clear_full_ptes() might be 
problematic across folios.


-- 
Cheers,

David / dhildenb