Re: [PATCH v6 01/13] mm/migrate_device: Introduce migrate_pfn_from_page() helper

David Hildenbrand (Arm)
2026-03-02T09:22:30Z

On 3/2/26 00:38, Jordan Niethe wrote:
> Hi,
>
> On 28/2/26 08:11, David Hildenbrand (Arm) wrote:
>> On 2/2/26 12:36, Jordan Niethe wrote:
>>> To create a migrate entry from a given struct page, that page is first
>>> converted to its pfn, before passing the pfn to migrate_pfn().
>>>
>>> A future change will remove device private pages from the physical
>>> address space. This will mean that device private pages no longer have a
>>> pfn and must be handled separately.
>>>
>>> Prepare for this with a new helper:
>>>
>>>      - migrate_pfn_from_page()
>>>
>>> This helper takes a struct page as parameter instead of a pfn. This will
>>> allow more flexibility for handling the mpfn differently for device
>>> private pages.
>>>
>>> Reviewed-by: Balbir Singh <balbirs@nvidia.com>
>>> Acked-by: Felix Kuehling <felix.kuehling@amd.com>
>>> Signed-off-by: Jordan Niethe <jniethe@nvidia.com>
>>> ---
>>
>> Acked-by: David Hildenbrand (Arm) <david@kernel.org>

I'll go through he remainder of the patchset this week.

While skimming over patch #2, I was wondering whether
"page_to_migration_pfn()" would better fit "migration_pfn_to_page".

... and I was wondering why that code deals with pages instead of folios.

E.g.,

page = folio_page(folio, 0);
mpfn[i] = migrate_pfn_from_page(page);

Should just be

mpfn[i] = folio_to_migration_pfn(folio);

Right?

--
Cheers,

David