Re: [PATCH] fs: push nr_cached_objects memcg gating into individual filesystems

[Shakeel Butt <shakeel.butt@linux.dev>]

On Tue, Jul 14, 2026 at 03:14:54AM -0700, Usama Arif wrote:
> Commit 0baad6f9b997 ("fs/super: skip non-memcg-aware nr_cached_objects
> in memcg slab shrink") added a check in fs/super.c that skips the
> ->nr_cached_objects() hook whenever the shrinker is invoked for a
> non-root memcg, because none of the current implementations (btrfs,
> xfs, shmem huge) honour sc->memcg.
> 
> That policy is really a filesystem-owned property: fs/super.c should
> not encode the assumption that these hooks are never memcg-aware,
> since a future implementation might legitimately filter by sc->memcg.
> Move the check into btrfs_nr_cached_objects(), xfs_fs_nr_cached_objects()
> and shmem_unused_huge_count() so each filesystem can lift the
> restriction independently once its underlying counters/scans become
> memcg-aware, without needing a coordinated change to fs/super.c.
> 
> Behaviour is unchanged: calls into these hooks from shrink_slab_memcg()
> still early-return 0 for non-root memcg contexts, keeping the shrinker
> bit clearable in each memcg's bitmap; the global (kswapd or root
> direct reclaim) path still drives them as before.
> 
> Signed-off-by: Usama Arif <usama.arif@linux.dev>

Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>