linux-kernel - Re: [PATCH v3 1/7] mm: Add folio_split

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Message-ID: <1319a24a-bcfc-47e5-a022-f5d00994acc9@kernel.org>
Date: Fri, 9 Jan 2026 14:26:05 +0100
From: "David Hildenbrand (Red Hat)" <david@...nel.org>
To: Francois Dugast <francois.dugast@...el.com>,
 intel-xe@...ts.freedesktop.org
Cc: dri-devel@...ts.freedesktop.org, Matthew Brost <matthew.brost@...el.com>,
 Balbir Singh <balbirs@...dia.com>, Andrew Morton
 <akpm@...ux-foundation.org>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Zi Yan <ziy@...dia.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, Nico Pache <npache@...hat.com>,
 Ryan Roberts <ryan.roberts@....com>, Dev Jain <dev.jain@....com>,
 Barry Song <baohua@...nel.org>, Lance Yang <lance.yang@...ux.dev>,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 Alistair Popple <apopple@...dia.com>
Subject: Re: [PATCH v3 1/7] mm: Add folio_split_unref helper

On 1/9/26 14:19, David Hildenbrand (Red Hat) wrote:
> On 1/9/26 09:54, Francois Dugast wrote:
>> From: Matthew Brost <matthew.brost@...el.com>
>>
>> Add folio_split_unref helper which splits an unreferenced folio
> 
> split_unref reads like "split and unref".
> 
> You probably want to call this something like "folio_split_frozen" ?
> 
> The very definition of "frozen" is "refcount = 0 ", so you can simplify
> the documentation.
> 
> Are the folios you want to pass in there completely unused (-> free) or
> might they still be in use (e.g., migration entries point at them during
> folio split)
> 
> So I am not sure yet if this should be "folio_split_frozen()" or
> "folio_split_freed()" or sth like that.
> 
> I'm not CCed on the other patches in the series or the cover letter, so
> I don't see the context.
> 

Ah, I was CCed on #3 where we call this function on folios that are 
getting freed.

In that case it would be acceptable to initialize folio->mapping (and 
folio->index?) of the split folios. Do we also have to initialize 
folio->flags, folio->private etc?

See __split_huge_page_tail().

folio_split_freed() would likely be best, because then it is clearer 
that there is absolutely no state to copy from the large folio.

> You should describe in this patch here in which context the function is
> supposed to be used in later commits.

-- 
Cheers

David