linux-kernel - Re: [PATCH v2 03/14] mm: Convert vmf_insert_mixed() from using pte_devmap to pte

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Message-ID: <051f769d-3a0e-409e-bd40-22000f10b986@redhat.com>
Date: Wed, 18 Jun 2025 11:31:02 +0200
From: David Hildenbrand <david@...hat.com>
To: Alistair Popple <apopple@...dia.com>, akpm@...ux-foundation.org
Cc: linux-mm@...ck.org, gerald.schaefer@...ux.ibm.com,
 dan.j.williams@...el.com, jgg@...pe.ca, willy@...radead.org,
 linux-kernel@...r.kernel.org, nvdimm@...ts.linux.dev,
 linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
 linux-xfs@...r.kernel.org, jhubbard@...dia.com, hch@....de,
 zhang.lyra@...il.com, debug@...osinc.com, bjorn@...nel.org,
 balbirs@...dia.com, lorenzo.stoakes@...cle.com,
 linux-arm-kernel@...ts.infradead.org, loongarch@...ts.linux.dev,
 linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
 linux-cxl@...r.kernel.org, dri-devel@...ts.freedesktop.org, John@...ves.net,
 m.szyprowski@...sung.com, Jason Gunthorpe <jgg@...dia.com>
Subject: Re: [PATCH v2 03/14] mm: Convert vmf_insert_mixed() from using
 pte_devmap to pte_special

On 17.06.25 11:49, David Hildenbrand wrote:
> On 16.06.25 13:58, Alistair Popple wrote:
>> DAX no longer requires device PTEs as it always has a ZONE_DEVICE page
>> associated with the PTE that can be reference counted normally. Other users
>> of pte_devmap are drivers that set PFN_DEV when calling vmf_insert_mixed()
>> which ensures vm_normal_page() returns NULL for these entries.
>>
>> There is no reason to distinguish these pte_devmap users so in order to
>> free up a PTE bit use pte_special instead for entries created with
>> vmf_insert_mixed(). This will ensure vm_normal_page() will continue to
>> return NULL for these pages.
>>
>> Architectures that don't support pte_special also don't support pte_devmap
>> so those will continue to rely on pfn_valid() to determine if the page can
>> be mapped.
>>
>> Signed-off-by: Alistair Popple <apopple@...dia.com>
>> Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
>> Reviewed-by: Dan Williams <dan.j.williams@...el.com>
>> ---

As Andrew notes offlined, there is no content here. I sent this by mistake
after replying to patch#6 instead.

-- 
Cheers,

David / dhildenb