Re: [PATCH v2 2/3] mm/madvise: skip zone device folios in cold/pageout PMD range

On 8/18/26 8:08 AM, 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.
> 
> Fixes: a30b48bf1b24 ("mm/migrate_device: implement THP migration of zone device pages")
> Cc: [email protected]
> Signed-off-by: Gregory Price (Meta) <[email protected]>
> Acked-by: David Hildenbrand (Arm) <[email protected]>
> Reviewed-by: Lorenzo Stoakes (ARM) <[email protected]>
> ---
>  mm/madvise.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/mm/madvise.c b/mm/madvise.c
> index c179938097bf0..2151bb9468594 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -396,6 +396,9 @@ 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;

Makes sense

Reviewed-by: Balbir Singh <[email protected]>