Re: [PATCH v2 05/11] mm/page_vma_mapped: Add flags to page_vma_mapped_walk::pfn to track device private pages

Jordan Niethe
2026-01-20T22:52:47Z

Hi,

On 21/1/26 09:49, Zi Yan wrote:
> On 20 Jan 2026, at 17:37, Jordan Niethe wrote:
>
>> Hi,
>>
>> On 14/1/26 06:44, Zi Yan wrote:
>>> On 7 Jan 2026, at 4:18, Jordan Niethe wrote:
>>>
>>>> A future change will remove device private pages from the physical
>>>> address space. This will mean that device private pages no longer have
>>>> normal PFN and must be handled separately.
>>>>
>>>> Prepare for this by modifying page_vma_mapped_walk::pfn to contain flags
>>>> as well as a PFN. Introduce a PVMW_PFN_DEVICE_PRIVATE flag to indicate
>>>> that a page_vma_mapped_walk::pfn contains a PFN for a device private
>>>> page.
>>>>
>>>> Signed-off-by: Jordan Niethe <jniethe@nvidia.com>
>>>> Signed-off-by: Alistair Popple <apopple@nvidia.com>
>>>> ---
>>>> v1:
>>>> - Update for HMM huge page support
>>>> v2:
>>>> - Move adding device_private param to check_pmd() until final patch
>>>> ---
>>>> include/linux/rmap.h | 30 +++++++++++++++++++++++++++++-
>>>> mm/page_vma_mapped.c | 13 +++++++------
>>>> mm/rmap.c | 4 ++--
>>>> mm/vmscan.c | 2 +-
>>>> 4 files changed, 39 insertions(+), 10 deletions(-)
>>>>
>>>> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
>>>> index daa92a58585d..57c63b6a8f65 100644
>>>> --- a/include/linux/rmap.h
>>>> +++ b/include/linux/rmap.h
>>>> @@ -939,9 +939,37 @@ struct page_vma_mapped_walk {
>>>> unsigned int flags;
>>>> };
>>>>
>>>> +/* pfn is a device private offset */
>>>> +#define PVMW_PFN_DEVICE_PRIVATE (1UL << 0)
>>>> +#define PVMW_PFN_SHIFT 1
>>>> +
>>>> +static inline unsigned long page_vma_walk_pfn(unsigned long pfn)
>>>> +{
>>>> + return (pfn << PVMW_PFN_SHIFT);
>>>> +}
>>>> +
>>>> +static inline unsigned long folio_page_vma_walk_pfn(const struct folio *folio)
>>>> +{
>>>> + if (folio_is_device_private(folio))
>>>> + return page_vma_walk_pfn(folio_pfn(folio)) |
>>>> + PVMW_PFN_DEVICE_PRIVATE;
>>>> +
>>>> + return page_vma_walk_pfn(folio_pfn(folio));
>>>> +}
>>>> +
>>>> +static inline struct page *page_vma_walk_pfn_to_page(unsigned long pvmw_pfn)
>>>> +{
>>>> + return pfn_to_page(pvmw_pfn >> PVMW_PFN_SHIFT);
>>>> +}
>>>> +
>>>> +static inline struct folio *page_vma_walk_pfn_to_folio(unsigned long pvmw_pfn)
>>>> +{
>>>> + return page_folio(page_vma_walk_pfn_to_page(pvmw_pfn));
>>>> +}
>>>> +
>>>> #define DEFINE_FOLIO_VMA_WALK(name, _folio, _vma, _address, _flags) \
>>>> struct page_vma_mapped_walk name = { \
>>>> - .pfn = folio_pfn(_folio), \
>>>> + .pfn = folio_page_vma_walk_pfn(_folio), \
>>>> .nr_pages = folio_nr_pages(_folio), \
>>>> .pgoff = folio_pgoff(_folio), \
>>>> .vma = _vma, \
>>>> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
>>>> index b38a1d00c971..96c525785d78 100644
>>>> --- a/mm/page_vma_mapped.c
>>>> +++ b/mm/page_vma_mapped.c
>>>> @@ -129,9 +129,9 @@ static bool check_pte(struct page_vma_mapped_walk *pvmw, unsigned long pte_nr)
>>>> pfn = softleaf_to_pfn(entry);
>>>> }
>>>>
>>>> - if ((pfn + pte_nr - 1) < pvmw->pfn)
>>>> + if ((pfn + pte_nr - 1) < (pvmw->pfn >> PVMW_PFN_SHIFT))
>>>
>>> Can you add a helper function for (pvmw->pfn >> PVMW_PFN_SHIFT)? It is impossible
>>> to tell why pfn does not need >> PVMW_PFN_SHIFT.
>>
>> Sure, something like page_vma_walk_pfn_to_offset()?
>>
>
> Just page_vma_walk_pfn(pvmw)? Since the code is comparing with pfn.

Sure, that works.

Thanks,
Jordan.

>
> Best Regards,
> Yan, Zi