[PATCH 2/5] mm: rmap: add a ZONE_DEVICE folio warning in folio_referenced()

[Alistair Popple]

On 2026-02-24 at 12:56 +1100, Baolin Wang <baolin.wang at linux.alibaba.com> wrote...
> The folio_referenced() is used to test whether a folio was referenced during
> reclaim. Moreover, ZONE_DEVICE folios are controlled by their device driver,
> have a lifetime tied to that driver, and are never placed on the LRU list.
> That means we should never try to reclaim ZONE_DEVICE folios, so add a warning
> to catch this unexpected behavior in folio_referenced() to avoid confusion,
> as discussed in the previous thread[1].

Agree with this so one you've handled Rik's comment feel free to add:

Reviewed-by: Alistair Popple <apopple at nvidia.com>

> [1] https://lore.kernel.org/all/16fb7985-ec0f-4b56-91e7-404c5114f899@kernel.org/
> Signed-off-by: Baolin Wang <baolin.wang at linux.alibaba.com>
> ---
>  mm/rmap.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/mm/rmap.c b/mm/rmap.c
> index bff8f222004e..be785dfc9336 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1065,6 +1065,7 @@ int folio_referenced(struct folio *folio, int is_locked,
>  		.invalid_vma = invalid_folio_referenced_vma,
>  	};
>  
> +	VM_WARN_ON_FOLIO(folio_is_zone_device(folio), folio);
>  	*vm_flags = 0;
>  	if (!pra.mapcount)
>  		return 0;
> -- 
> 2.47.3
> 
>