Re: [PATCH v2 03/47] mm: shrinker: add infrastructure for dynamically allocating shrinker

[Qi Zheng]

Hi Peter,

On 2023/7/24 20:25, Peter Zijlstra wrote:
> On Mon, Jul 24, 2023 at 05:43:10PM +0800, Qi Zheng wrote:
>
> > +void shrinker_unregister(struct shrinker *shrinker)
> > +{
> > +	struct dentry *debugfs_entry;
> > +	int debugfs_id;
> > +
> > +	if (!shrinker || !(shrinker->flags & SHRINKER_REGISTERED))
> > +		return;
> > +
> > +	down_write(&shrinker_rwsem);
> > +	list_del(&shrinker->list);
> > +	shrinker->flags &= ~SHRINKER_REGISTERED;
> > +	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> > +		unregister_memcg_shrinker(shrinker);
> > +	debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id);
> > +	up_write(&shrinker_rwsem);
> > +
> > +	shrinker_debugfs_remove(debugfs_entry, debugfs_id);
>
> Should there not be an rcu_barrier() right about here?

The shrinker_debugfs_remove() will wait for debugfs_file_put() to
return, so when running here, all shrinker debugfs operations have
been completed. And the slab shrink will hold the read lock of
shrinker_rwsem to traverse the shrinker_list, so when we hold the
write lock of shrinker_rwsem to delete the shrinker from the
shrinker_list, the shrinker will not be executed again.

So I think there is no need to add a rcu_barrier() here. Please let
me know if I missed something.

Thanks,
Qi

> > +
> > +	kfree(shrinker->nr_deferred);
> > +	shrinker->nr_deferred = NULL;
> > +
> > +	kfree(shrinker);
> > +}
> > +EXPORT_SYMBOL(shrinker_unregister);