Re: [PATCH 1/4] mm/damon: defensively skip zone device folios in damon_get_folio()

["Lorenzo Stoakes (ARM)" <ljs@kernel.org>]

On Tue, Jul 28, 2026 at 03:47:11PM -0400, Gregory Price wrote:
> All DAMON physical- and virtual-address operations obtain their folios
> through damon_get_folio(). That helper already excludes ZONE_DEVICE
> memory implicitly via pfn_to_online_page() and folio_test_lru(), but
> this is inconsistent with other callers in mm/ which test explicitly.
>
> Add an explicit folio_is_zone_device() rejection in damon_get_folio()
> so the guarantee lives in one place and covers every caller uniformly,
> consistent with other mm walkers that reject zone device folios.
>
> Signed-off-by: Gregory Price (Meta) <gourry@gourry.net>

Thanks, nice to make it explicit!

Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>

> ---
>  mm/damon/ops-common.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c
> index d7d7f100389b..d8bca7355b4f 100644
> --- a/mm/damon/ops-common.c
> +++ b/mm/damon/ops-common.c
> @@ -32,7 +32,8 @@ struct folio *damon_get_folio(unsigned long pfn)
>  	folio = page_folio(page);
>  	if (!folio_try_get(folio))
>  		return NULL;
> -	if (unlikely(page_folio(page) != folio) || !folio_test_lru(folio)) {
> +	if (unlikely(page_folio(page) != folio) || !folio_test_lru(folio) ||
> +	    folio_is_zone_device(folio)) {
>  		folio_put(folio);
>  		folio = NULL;
>  	}
> --
> 2.55.0
>

--
Cheers, Lorenzo