Re: [PATCH 1/4] migrate: Allow migrate_misplaced_folio APIs without a VMA

[Raghavendra K T <raghavendra.kt@amd.com>]

On 11/27/2024 1:51 PM, Gregory Price wrote:
> To migrate unmapped pagecache folios, migrate_misplaced_folio and
> migrate_misplaced_folio_prepare must handle folios without VMAs.
> 
> migrate_misplaced_folio_prepare checks VMA for exec bits, so allow
> a NULL VMA when it does not have a mapping.
> 
> migrate_misplaced_folio must call migrate_pages with MIGRATE_SYNC
> when in the pagecache path because it is a synchronous context.
> 
> Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
> Signed-off-by: Gregory Price <gourry@gourry.net>
> ---
>   mm/migrate.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/migrate.c b/mm/migrate.c
> index dfb5eba3c522..3b0bd3f21ac3 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2632,7 +2632,7 @@ int migrate_misplaced_folio_prepare(struct folio *folio,
>   		 * See folio_likely_mapped_shared() on possible imprecision
>   		 * when we cannot easily detect if a folio is shared.
>   		 */
> -		if ((vma->vm_flags & VM_EXEC) &&
> +		if (vma && (vma->vm_flags & VM_EXEC) &&
>   		    folio_likely_mapped_shared(folio))
>   			return -EACCES;
>   

Thanks for this patch.

This would be helpful in the cases of independent page scanning
algorithms where we do not have a VMA associated with that.

Hopefully it can be taken to tree independently.
Feel free to add.

Reviewed-by: Raghavendra K T <raghavendra.kt@amd.com>