linux-kernel - Re: [PATCH v2 05/11] mm/page_vma_mapped: Add flags to page_vma_mapped

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Message-ID: <09a8d599-4612-4ee6-b71f-f2f356d4a14c@nvidia.com>
Date: Wed, 21 Jan 2026 09:52:29 +1100
From: Jordan Niethe <jniethe@...dia.com>
To: Zi Yan <ziy@...dia.com>
Cc: linux-mm@...ck.org, balbirs@...dia.com, matthew.brost@...el.com,
 akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
 dri-devel@...ts.freedesktop.org, david@...hat.com, apopple@...dia.com,
 lorenzo.stoakes@...cle.com, lyude@...hat.com, dakr@...nel.org,
 airlied@...il.com, simona@...ll.ch, rcampbell@...dia.com,
 mpenttil@...hat.com, jgg@...dia.com, willy@...radead.org,
 linuxppc-dev@...ts.ozlabs.org, intel-xe@...ts.freedesktop.org, jgg@...pe.ca,
 Felix.Kuehling@....com
Subject: Re: [PATCH v2 05/11] mm/page_vma_mapped: Add flags to
 page_vma_mapped_walk::pfn to track device private pages

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@...dia.com>
>>>> Signed-off-by: Alistair Popple <apopple@...dia.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