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

Jordan Niethe
2026-01-20T22:37:26Z

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()?

Thanks,
Jordan.

>
>> return false;
>> - if (pfn > (pvmw->pfn + pvmw->nr_pages - 1))
>> + if (pfn > ((pvmw->pfn >> PVMW_PFN_SHIFT) + pvmw->nr_pages - 1))
>
> Ditto.
>
>> return false;
>> return true;
>> }
>> @@ -139,9 +139,9 @@ static bool check_pte(struct page_vma_mapped_walk *pvmw, unsigned long pte_nr)
>> /* Returns true if the two ranges overlap. Careful to not overflow. */
>> static bool check_pmd(unsigned long pfn, struct page_vma_mapped_walk *pvmw)
>> {
>> - if ((pfn + HPAGE_PMD_NR - 1) < pvmw->pfn)
>> + if ((pfn + HPAGE_PMD_NR - 1) < (pvmw->pfn >> PVMW_PFN_SHIFT))
>
> Ditto.
>> return false;
>> - if (pfn > pvmw->pfn + pvmw->nr_pages - 1)
>> + if (pfn > (pvmw->pfn >> PVMW_PFN_SHIFT) + pvmw->nr_pages - 1)
>
> Ditto.
>> return false;
>> return true;
>> }
>> @@ -254,7 +254,8 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
>> entry = softleaf_from_pmd(pmde);
>>
>> if (!softleaf_is_migration(entry) ||
>> - !check_pmd(softleaf_to_pfn(entry), pvmw))
>> + !check_pmd(softleaf_to_pfn(entry),
>> + pvmw))
>> return not_found(pvmw);
>> return true;
>> }
>> @@ -350,7 +351,7 @@ unsigned long page_mapped_in_vma(const struct page *page,
>> {
>> const struct folio *folio = page_folio(page);
>> struct page_vma_mapped_walk pvmw = {
>> - .pfn = page_to_pfn(page),
>> + .pfn = folio_page_vma_walk_pfn(folio),
>> .nr_pages = 1,
>> .vma = vma,
>> .flags = PVMW_SYNC,
>> diff --git a/mm/rmap.c b/mm/rmap.c
>> index f955f02d570e..79a2478b4aa9 100644
>> --- a/mm/rmap.c
>> +++ b/mm/rmap.c
>> @@ -1112,7 +1112,7 @@ static bool mapping_wrprotect_range_one(struct folio *folio,
>> {
>> struct wrprotect_file_state *state = (struct wrprotect_file_state *)arg;
>> struct page_vma_mapped_walk pvmw = {
>> - .pfn = state->pfn,
>> + .pfn = page_vma_walk_pfn(state->pfn),
>> .nr_pages = state->nr_pages,
>> .pgoff = state->pgoff,
>> .vma = vma,
>> @@ -1190,7 +1190,7 @@ int pfn_mkclean_range(unsigned long pfn, unsigned long nr_pages, pgoff_t pgoff,
>> struct vm_area_struct *vma)
>> {
>> struct page_vma_mapped_walk pvmw = {
>> - .pfn = pfn,
>> + .pfn = page_vma_walk_pfn(pfn),
>> .nr_pages = nr_pages,
>> .pgoff = pgoff,
>> .vma = vma,
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index 670fe9fae5ba..be5682d345b5 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -4203,7 +4203,7 @@ bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
>> pte_t *pte = pvmw->pte;
>> unsigned long addr = pvmw->address;
>> struct vm_area_struct *vma = pvmw->vma;
>> - struct folio *folio = pfn_folio(pvmw->pfn);
>> + struct folio *folio = page_vma_walk_pfn_to_folio(pvmw->pfn);
>> struct mem_cgroup *memcg = folio_memcg(folio);
>> struct pglist_data *pgdat = folio_pgdat(folio);
>> struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat);
>> --
>> 2.34.1
>
>
> Best Regards,
> Yan, Zi