linux-kernel - Re: [PATCH v2 8/9] mm: introduce and use vm_normal_page

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Message-ID: <889dade6-8b3d-4cce-93ec-827886f7cb2c@redhat.com>
Date: Fri, 18 Jul 2025 13:06:30 +0200
From: David Hildenbrand <david@...hat.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 xen-devel@...ts.xenproject.org, linux-fsdevel@...r.kernel.org,
 nvdimm@...ts.linux.dev, Andrew Morton <akpm@...ux-foundation.org>,
 Juergen Gross <jgross@...e.com>, Stefano Stabellini
 <sstabellini@...nel.org>,
 Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
 Dan Williams <dan.j.williams@...el.com>, Matthew Wilcox
 <willy@...radead.org>, Jan Kara <jack@...e.cz>,
 Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka
 <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
 Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
 Zi Yan <ziy@...dia.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>,
 Nico Pache <npache@...hat.com>, Ryan Roberts <ryan.roberts@....com>,
 Dev Jain <dev.jain@....com>, Barry Song <baohua@...nel.org>,
 Jann Horn <jannh@...gle.com>, Pedro Falcato <pfalcato@...e.de>,
 Hugh Dickins <hughd@...gle.com>, Oscar Salvador <osalvador@...e.de>,
 Lance Yang <lance.yang@...ux.dev>
Subject: Re: [PATCH v2 8/9] mm: introduce and use vm_normal_page_pud()

On 18.07.25 12:47, Lorenzo Stoakes wrote:
> On Thu, Jul 17, 2025 at 10:14:33PM +0200, David Hildenbrand wrote:
>> On 17.07.25 22:03, Lorenzo Stoakes wrote:
>>> On Thu, Jul 17, 2025 at 01:52:11PM +0200, David Hildenbrand wrote:
>>>> Let's introduce vm_normal_page_pud(), which ends up being fairly simple
>>>> because of our new common helpers and there not being a PUD-sized zero
>>>> folio.
>>>>
>>>> Use vm_normal_page_pud() in folio_walk_start() to resolve a TODO,
>>>> structuring the code like the other (pmd/pte) cases. Defer
>>>> introducing vm_normal_folio_pud() until really used.
>>>
>>> I mean fine :P but does anybody really use this?
>>
>> This is a unified PFN walker (!hugetlb + hugetlb), so you can easily run
>> into hugetlb PUDs, DAX PUDs and huge pfnmap (vfio) PUDs :)
> 
> Ahhh ok. I hate hugetlb so very very much.
> 
> Oscar is doing the Lord's work improving things but the trauma is still
> there... :P
> 
> Also yeah DAX ahem.
> 
> I'm not familiar with huge pfnmap PUDs, could you give me a hint on this? :>)

vmf_insert_pfn_pmd(), called from  drivers/vfio/pci/vfio_pci_core.c

Essentially, we create huge PUDs when mapping device BARs to user space.

-- 
Cheers,

David / dhildenb