Re: [PATCH v4 1/4] fs: fix missed removal of super_fs_objects_eligible()

[Qi Zheng]

Hi Andrew,

On 8/30/26 7:23 AM, Andrew Morton wrote:
> On Sat, 29 Aug 2026 09:49:44 +0800 Qi Zheng <qi.zheng@xxxxxxxxx> wrote:
>
> > Hi Andrew,
> >
> > On 8/29/26 2:41 AM, Andrew Morton wrote:
> > > On Mon, 17 Aug 2026 17:03:25 +0800 Qi Zheng <qi.zheng@xxxxxxxxx> wrote:
> > >
> > > > From: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
> > > >
> > > > Commit 0ef8faff490be ("fs: push nr_cached_objects memcg gating into
> > > > individual filesystems") forgot to drop the super_fs_objects_eligible(),
> > > > just fix it.
> > >
> > > Oh.  Why?  Please can we have a description of what's wrong with the
> > > current code?
> >
> > As I replied in another thread [1], this fix and commit 0ef8faff490be
> > together make up the complete patch originally sent by Usama [2], so
> > they should be squashed together.
>
> 0ef8faff490be is upstream so they can't be squashed!

So sad.

> > Without this fix, all memcg-aware
> > nr_cached_objects() will be skipped during memcg-level shrinking.
> > Besides the newly added memcg-aware shmem huge shrinker, XFS will also
> > run into issues.
>
> OK, please add this info to this patch's changelog.  Please also decide
> whether a cc:stable should be added and if so, ensure the changelog
> makes clear why we're recommending a backport.
>
> As part of this, let's expand on "XFS will also run into issues".

How about this instead:

---
Commit 0ef8faff490be ("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 0ef8faff490be 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 0baad6f9b997 ("fs/super: skip non-memcg-aware
    nr_cached_objects in memcg slab shrink") that 0ef8faff490be 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
0ef8faff490be actually takes effect.

Fixes: 0ef8faff490be ("fs: push nr_cached_objects memcg gating into 
individual filesystems")
Cc: stable@xxxxxxxxxxxxxxx
---

Can you fix up the commit message directly on your end? Let me know if
you prefer me to spin a v5 instead.

Thank,
Qi

> Thanks.