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

[Usama Arif <usama.arif@linux.dev>]

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?

Thanks,
Usama