Re: [PATCH 3/4] mm/madvise: skip zone device folios in cold/pageout PMD range

[Lorenzo Stoakes (ARM)]

On Tue, Jul 28, 2026 at 03:47:13PM -0400, Gregory Price wrote:
> madvise_cold_or_pageout_pte_range() resolves the folio backing a PMD
> via pmd_folio() and ages or reclaims it without checking for zone
> device memory.
>
> The surrounding guards do not cover every zone device case:
>
>   - can_madv_lru_vma() excludes VM_PFNMAP and VM_HUGETLB VMAs
>     (so device DAX is filtered)
>
>   - !pmd_present() branch above rejects device-private and
>     migration entries, which are non-present.
>
>   - A present zone device PMD - e.g. a device-coherent THP - is
>     not filtered by any of these, nor by pmd_folio() (unlike
>     vm_normal_page_pmd(), it performs no special/pfnmap check),
>     and would be aged or paged out here.
>
> Skip ZONE_DEVICE folios explicitly during MADV_COLD/PAGEOUT.
>
> Signed-off-by: Gregory Price (Meta) <gourry@xxxxxxxxxx>

LGTM so:

Reviewed-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>

> ---
>  mm/madvise.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/mm/madvise.c b/mm/madvise.c
> index 07a21ca31bad..ffd6a68320a8 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -395,6 +395,9 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
>
>  		folio = pmd_folio(orig_pmd);
>
> +		if (folio_is_zone_device(folio))
> +			goto huge_unlock;
> +
>  		/* Do not interfere with other mappings of this folio */
>  		if (folio_maybe_mapped_shared(folio))
>  			goto huge_unlock;
> --
> 2.55.0
>

--
Cheers, Lorenzo