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

["David Hildenbrand (Arm)" <david@kernel.org>]

On 9/4/26 05:35, 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@linux.alibaba.com/
> 
> Fixes: fafaeceb89a5 ("mm: switch deferred split shrinker to list_lru")
> Suggested-by: Michal Koutný <mkoutny@suse.com>
> Signed-off-by: Qinyun Tan <qinyuntan@linux.alibaba.com>
> ---

Acked-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David