Re: [PATCH 29/29] mm: shrinker: move shrinker-related code into a separate file

Qi Zheng
2023-06-23T13:25:15Z

Hi Sergey,

On 2023/6/23 13:25, Sergey Senozhatsky wrote:
> On (23/06/22 16:53), Qi Zheng wrote:
>> +/*
>> + * Remove one
>> + */
>> +void unregister_shrinker(struct shrinker *shrinker)
>> +{
>> + struct dentry *debugfs_entry;
>> + int debugfs_id;
>> +
>> + if (!(shrinker->flags & SHRINKER_REGISTERED))
>> + return;
>> +
>> + shrinker_put(shrinker);
>> + wait_for_completion(&shrinker->completion_wait);
>> +
>> + mutex_lock(&shrinker_mutex);
>> + list_del_rcu(&shrinker->list);
>
> Should this function wait for RCU grace period(s) before it goes
> touching shrinker fields?

Why? We will free this shrinker instance by rcu after executing
unregister_shrinker(). So it is safe to touch shrinker fields here.

>
>> + shrinker->flags &= ~SHRINKER_REGISTERED;
>> + if (shrinker->flags & SHRINKER_MEMCG_AWARE)
>> + unregister_memcg_shrinker(shrinker);
>> + debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id);
>> + mutex_unlock(&shrinker_mutex);
>> +
>> + shrinker_debugfs_remove(debugfs_entry, debugfs_id);
>> +
>> + kfree(shrinker->nr_deferred);
>> + shrinker->nr_deferred = NULL;
>> +}
>> +EXPORT_SYMBOL(unregister_shrinker);
>
> [..]
>
>> +void shrinker_free(struct shrinker *shrinker)
>> +{
>> + kfree(shrinker);
>> +}
>> +EXPORT_SYMBOL(shrinker_free);
>> +
>> +void unregister_and_free_shrinker(struct shrinker *shrinker)
>> +{
>> + unregister_shrinker(shrinker);
>> + kfree_rcu(shrinker, rcu);
>> +}
>
> Seems like this
>
> unregister_shrinker();
> shrinker_free();
>
> is not exact equivalent of this
>
> unregister_and_free_shrinker();

Yes, my original intention is that shrinker_free() is only used to
handle the case where register_shrinker() returns failure.

I will implement the method suggested by Dave in 02/29. Those APIs are
more concise and will bring more benefits. :)

Thanks,
Qi