Re: [PATCH] fs/super: skip non-memcg-aware nr_cached_objects in memcg slab shrink

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

Hi Usama,

On 7/13/26 11:34 PM, Usama Arif wrote:
> 
> 
> On 13/07/2026 14:12, Qi Zheng wrote:
>> Hi Usama,
>>
>> On 6/9/26 8:30 PM, Usama Arif wrote:
>>> The super_block shrinker is registered with SHRINKER_MEMCG_AWARE because its
>>> dentry and inode LRUs are memcg-aware (via list_lru). But the optional
>>> ->nr_cached_objects() hooks that the shrinker also drives are not memcg-aware:
>>> btrfs extent maps and xfs inode reclaim operate on filesystem-global
>>> state, and shmem's unused-huge shrinker walks a per-superblock shrinklist.
>>> None of them filter by sc->memcg.
>>
>> This makes sense for now, but how should we handle this if these
>> shrinkers are made memcg-aware in the future?
>>
>> I've recently been working on making the shmem huge shrinker
>> memcg-aware, but noticed my changes broke after rebasing onto the latest
>> tree, which led me to this patch.
>>
>> As for the shmem huge shrinker, I can work around this limitation by
>> making it a separate shrinker. But this feels more like an overall
>> design decision, effectively meaning that all nr_cached_objects are
>> precluded from being memcg-aware.
>>
>> Thanks,
>> Qi
>>
> 
> 
> Hi Qi,
> 
> Thanks for raising this. I think the alternative is what I mentioned in
> https://lore.kernel.org/all/cfdb8620-ea55-4226-98bf-d006820e6270@linux.dev/
> move this down to the fs own callbacks instead of here. Would that
> be better?

Yes, I think this is a better approach.

Later on, shrinkers that are converted to be memcg-aware can lift this 
restriction themselves.

Thanks,
Qi

> 
> Thanks,
> Usama