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

Zi Yan
2026-01-13T19:44:45Z

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.

> 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