Re: [PATCH 3/3] fs/proc/task_mmu: account device-private PMDs as present in smaps

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

On Wed, Nov 11, 2026 at 03:38:31AM -0800, Usama Arif wrote:
> Device-private PMDs represent mapped pages, but smaps_pmd_entry()
> passes present=false to smaps_account(). That treats them like migration
> entries: mapcounts are ignored, PSS is charged in full, and exclusive
> mappings are accounted as shared.
>
> Match smaps_pte_entry() and mark device-private PMDs as present so
> smaps_account() uses mapcounts for PSS and private/shared accounting.
>
> Fixes: a30b48bf1b24 ("mm/migrate_device: implement THP migration of zone device pages")
> Cc: stable@vger.kernel.org
> Signed-off-by: Usama Arif <usama.arif@linux.dev>

It feels like PMD level device private entries have been the source of a lot of
issues, maybe a good area to audit in general... :)

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

> ---
>  fs/proc/task_mmu.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index c0d391186c2b8..ad97532fc1184 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -1032,8 +1032,11 @@ static void smaps_pmd_entry(pmd_t *pmd, unsigned long addr,
>  	} else if (unlikely(thp_migration_supported())) {
>  		const softleaf_t entry = softleaf_from_pmd(*pmd);
>
> -		if (softleaf_has_pfn(entry))
> +		if (softleaf_has_pfn(entry)) {
> +			if (softleaf_is_device_private(entry))
> +				present = true;
>  			page = softleaf_to_page(entry);
> +		}
>  	}
>  	if (IS_ERR_OR_NULL(page))
>  		return;
> --
> 2.53.0-Meta
>

--
Cheers, Lorenzo