linux-kernel - Re: [PATCH] mm/rmap: Add anon

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Message-ID: <d6781e05-bde6-490c-af79-97993ed9018e@redhat.com>
Date: Fri, 25 Jul 2025 13:31:22 +0200
From: David Hildenbrand <david@...hat.com>
To: Jann Horn <jannh@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Rik van Riel
 <riel@...riel.com>, "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 Vlastimil Babka <vbabka@...e.cz>, Harry Yoo <harry.yoo@...cle.com>,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/rmap: Add anon_vma lifetime debug check

On 25.07.25 13:24, Jann Horn wrote:
> On Fri, Jul 25, 2025 at 1:12 PM David Hildenbrand <david@...hat.com> wrote:
>> On 25.07.25 13:08, Jann Horn wrote:
>>> On Thu, Jul 24, 2025 at 11:56 PM David Hildenbrand <david@...hat.com> wrote:
>>>> 2) We have a folio here, so ... better
>>>>
>>>> if (folio_test_anon(folio) && !folio_test_ksm(folio)) {
>>>>           ...
>>>> }
>>>
>>> Hrm, okay. It kind of irks me to write it as two checks when really I
>>> want to ask "is it this one specific type", but yeah, will change it.
>>
>> Well, ksm is a subtype of anon.
> 
> I mean... not really? At least ksm folios are not a subtype of normal
> anon folios. 

Well, what I mean is:

A KSM folio is considered an anon folio.

An anon folio is not necessarily a KSM folio.

Of course, there are implementation differences when it comes to 
folio->mapping etc, just the way the rmap works.

-- 
Cheers,

David / dhildenb