Re: [PATCH] mm/vmscan: drop checking if _deferred_list is empty before using TTU_SYNC

[David Hildenbrand <david@redhat.com>]

On 30.06.24 01:41, Barry Song wrote:
> From: Barry Song <v-songbaohua@oppo.com>
> 
> The optimization of list_empty(&folio->_deferred_list) aimed to prevent
> increasing the PTL duration when a large folio is partially unmapped,
> for example, from subpage 0 to subpage (nr - 2).
> 
> But Ryan's commit 5ed890ce5147 ("mm: vmscan: avoid split during
> shrink_folio_list()") actually splits this kind of large folios. This
> makes the "optimization" useless.
> 
> Signed-off-by: Barry Song <v-songbaohua@oppo.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Ryan Roberts <ryan.roberts@arm.com>
> ---
>   -v1
>   * I remember David and Ryan once suggested that this check could be dropped
>     while the patch was being pulled into mm-unstable. However, for some reason,
>     I forgot to request squashing this change.
> 
>   mm/vmscan.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 3d4c681c6d40..0761f91b407f 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1291,7 +1291,7 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
>   			 * try_to_unmap acquire PTL from the first PTE,
>   			 * eliminating the influence of temporary PTE values.
>   			 */
> -			if (folio_test_large(folio) && list_empty(&folio->_deferred_list))
> +			if (folio_test_large(folio))
>   				flags |= TTU_SYNC;
>   
>   			try_to_unmap(folio, flags);

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb