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

[Jordan Niethe <jniethe@nvidia.com>]

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