linux-kernel - Re: [PATCH v3 20/20] mm: stop maintaining the per-page mapcount of large folios (CONFIG_NO_PAGE

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Message-ID: <f9d19f72-58f7-4694-ae18-1d944238a3e7@redhat.com>
Date: Tue, 14 Oct 2025 16:38:38 +0200
From: David Hildenbrand <david@...hat.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: Wei Yang <richard.weiyang@...il.com>, linux-kernel@...r.kernel.org,
 linux-doc@...r.kernel.org, cgroups@...r.kernel.org, linux-mm@...ck.org,
 linux-fsdevel@...r.kernel.org, linux-api@...r.kernel.org,
 Andrew Morton <akpm@...ux-foundation.org>, Tejun Heo <tj@...nel.org>,
 Zefan Li <lizefan.x@...edance.com>, Johannes Weiner <hannes@...xchg.org>,
 Michal Koutný <mkoutny@...e.com>,
 Jonathan Corbet <corbet@....net>, Andy Lutomirski <luto@...nel.org>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 Muchun Song <muchun.song@...ux.dev>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>
Subject: Re: [PATCH v3 20/20] mm: stop maintaining the per-page mapcount of
 large folios (CONFIG_NO_PAGE_MAPCOUNT)

On 14.10.25 16:32, Matthew Wilcox wrote:
> On Tue, Oct 14, 2025 at 02:59:30PM +0200, David Hildenbrand wrote:
>>> As commit 349994cf61e6 mentioned, we don't support partially mapped PUD-sized
>>> folio yet.
>>
>> We do support partially mapped PUD-sized folios I think, but not anonymous
>> PUD-sized folios.
> 
> I don't think so?  The only mechanism I know of to allocate PUD-sized
> chunks of memory is hugetlb, and that doesn't permit partial mappings.

Greetings from the latest DAX rework :)

-- 
Cheers

David / dhildenb