Re: [PATCH 1/2] mm: thp: restore SHRINKER_NONSLAB on the deferred split shrinker

[Usama Arif]

On 04/09/2026 04:35, Qinyun Tan wrote:
> On a system booted with cgroup.memory=nokmem, the deferred split
> shrinker is quietly demoted to a non-memcg-aware one.  As a result,
> partially unmapped THPs are only split under global reclaim; memcg
> (limit-induced) reclaim never splits them, so a cgroup under memory
> pressure keeps its underused THPs intact.
> 
> This is a regression from commit fafaeceb89a5 ("mm: switch deferred
> split shrinker to list_lru"), which re-registered the shrinker without
> SHRINKER_NONSLAB.  The shrinker had carried this flag since commit
> 0a432dcbeb32 ("mm: shrinker: make shrinker not depend on memcg kmem")
> precisely so it would keep working with kmem accounting disabled.
> Without the flag, shrinker_memcg_alloc() fails with -ENOSYS under
> nokmem and the shrinker loses its memcg awareness.
> 
> This was noticed by Michal during review of the patch "mm/list_lru:
> don't copy stale shrinker id from non-memcg-aware shrinkers" [1].
> 
> Restore the flag.
> 
> [1] https://lore.kernel.org/lkml/697713c4-0857-485b-aba7-c74f37a3c8b4@xxxxxxxxxxxxxxxxx/
> 
> Fixes: fafaeceb89a5 ("mm: switch deferred split shrinker to list_lru")
> Suggested-by: Michal Koutný <mkoutny@xxxxxxxx>
> Signed-off-by: Qinyun Tan <qinyuntan@xxxxxxxxxxxxxxxxx>
> ---
>  mm/huge_memory.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 644d6905b49cc..16f9aa5b2d077 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1022,7 +1022,8 @@ int folio_memcg_alloc_deferred(struct folio *folio)
>  static int __init thp_shrinker_init(void)
>  {
>  	deferred_split_shrinker = shrinker_alloc(SHRINKER_NUMA_AWARE |
> -						 SHRINKER_MEMCG_AWARE,
> +						 SHRINKER_MEMCG_AWARE |
> +						 SHRINKER_NONSLAB,
>  						 "thp-deferred_split");
>  	if (!deferred_split_shrinker)
>  		return -ENOMEM;

Acked-by: Usama Arif <usama.arif@xxxxxxxxx>