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

[Qi Zheng <qi.zheng@linux.dev>]

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@linux.dev> 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@linux.dev> wrote:
>>>
>>>> From: Qi Zheng <zhengqi.arch@bytedance.com>
>>>>
>>>> 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@vger.kernel.org
---

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.
>