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fs: fix missed removal of super_fs_objects_eligible()

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Commit 0ef8faff49 ("fs: push nr_cached_objects memcg gating into
individual filesystems") was meant to drop the blanket memcg gate in
fs/super.c and let each ->nr_cached_objects() implementation decide for
itself whether it is meaningful in per-memcg reclaim.  However, when
that patch was applied the removal of super_fs_objects_eligible() and
its two call sites in super_cache_scan() / super_cache_count() was
lost, so the helper is still gating every ->nr_cached_objects() hook
and 0ef8faff49 is effectively a no-op.

Consequences of the leftover gate:

   - XFS's inode-reclaim hook, which is intentionally driven from
     per-memcg contexts to free memcg-charged slab, is still
     short-circuited in fs/super.c  exactly the regression from
     commit 0baad6f9b9 ("fs/super: skip non-memcg-aware
     nr_cached_objects in memcg slab shrink") that 0ef8faff49 was
     written to undo. Memcg-charged XFS inode slab therefore keeps
     piling up under per-memcg pressure until global reclaim kicks in.

   - Any future ->nr_cached_objects()/->free_cached_objects() that
     grows memcg awareness is likewise blocked before it can run, so
     filesystems cannot opt in to per-memcg reclaim on their own 
     defeating the whole point of pushing the gating decision down
     into the callbacks.

Drop the leftover helper and its call sites so the intent of
0ef8faff49 actually takes effect.

Link: https://lore.kernel.org/cover.1786955972.git.zhengqi.arch@bytedance.com
Link: https://lore.kernel.org/3b038d373c70ebac7cdabfb0035bb91d1d6e6cfe.1786955972.git.zhengqi.arch@bytedance.com
Link: https://lore.kernel.org/all/20260715103516.2410175-1-usama.arif@linux.dev/ [0]
Fixes: 0ef8faff49 ("fs: push nr_cached_objects memcg gating into individual filesystems")
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Acked-by: Usama Arif <usama.arif@linux.dev>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Qi Zheng 2026-08-17 17:03:25 +08:00 committed by Andrew Morton
parent 848d2ce2fc
commit 641aade99f
1 changed files with 2 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
fs/super.c
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@ -171,19 +171,6 @@ static void super_wake(struct super_block *sb, unsigned int flag)
wake_up_var(&sb->s_flags);
}
/*
* The s_op->nr_cached_objects hooks (used for example by btrfs and xfs)
* operate on filesystem-global state and ignore sc->memcg. Driving them
* from per-memcg shrink_slab_memcg() invocations only burns CPU walking
* per-cpu counters and queueing duplicate work: the actual reclaim happens on
* the global path (kswapd or root direct reclaim) regardless. Restrict them
* to that path.
*/
static inline bool super_fs_objects_eligible(struct shrink_control *sc)
{
return !sc->memcg || mem_cgroup_is_root(sc->memcg);
}
/*
* One thing we have to be careful of with a per-sb shrinker is that we don't
* drop the last active reference to the superblock from within the shrinker.
@ -213,7 +200,7 @@ static unsigned long super_cache_scan(struct shrinker *shrink,
if (!super_trylock_shared(sb))
return SHRINK_STOP;
if (sb->s_op->nr_cached_objects && super_fs_objects_eligible(sc))
if (sb->s_op->nr_cached_objects)
fs_objects = sb->s_op->nr_cached_objects(sb, sc);
inodes = list_lru_shrink_count(&sb->s_inode_lru, sc);
@ -274,8 +261,7 @@ static unsigned long super_cache_count(struct shrinker *shrink,
return 0;
smp_rmb();
if (sb->s_op && sb->s_op->nr_cached_objects &&
super_fs_objects_eligible(sc))
if (sb->s_op && sb->s_op->nr_cached_objects)
total_objects = sb->s_op->nr_cached_objects(sb, sc);
total_objects += list_lru_shrink_count(&sb->s_dentry_lru, sc);