Re: [PATCH 03/12] mm/pagewalk: Skip dax pages in pagewalk

David Hildenbrand
2025-05-30T09:42:56Z

On 29.05.25 08:32, Alistair Popple wrote:
> Previously dax pages were skipped by the pagewalk code as pud_special() or
> vm_normal_page{_pmd}() would be false for DAX pages. Now that dax pages are
> refcounted normally that is no longer the case, so add explicit checks to
> skip them.

Is this really what we want, though? If these are now just "normal"
pages, they shall be handled as being normal.

I would assume that we want to check that in the callers instead.

E.g., in get_mergeable_page() we already have a folio_is_zone_device()
check.

>
> Signed-off-by: Alistair Popple <apopple@nvidia.com>
> ---
> include/linux/memremap.h | 11 +++++++++++
> mm/pagewalk.c | 12 ++++++++++--
> 2 files changed, 21 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/memremap.h b/include/linux/memremap.h
> index 4aa1519..54e8b57 100644
> --- a/include/linux/memremap.h
> +++ b/include/linux/memremap.h
> @@ -198,6 +198,17 @@ static inline bool folio_is_fsdax(const struct folio *folio)
> return is_fsdax_page(&folio->page);
> }
>
> +static inline bool is_devdax_page(const struct page *page)
> +{
> + return is_zone_device_page(page) &&
> + page_pgmap(page)->type == MEMORY_DEVICE_GENERIC;
> +}
> +
> +static inline bool folio_is_devdax(const struct folio *folio)
> +{
> + return is_devdax_page(&folio->page);
> +}

Hm, nobody uses folio_is_devdax() in this patch :)

--
Cheers,

David / dhildenb