Re: [PATCH v2] mm, shrinker: make shrinker_list lockless

[Shakeel Butt]

On Thu, Nov 9, 2017 at 1:46 PM, Tetsuo Handa
<penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote:
> Shakeel Butt wrote:
>> > If you can accept serialized register_shrinker()/unregister_shrinker(),
>> > I think that something like shown below can do it.
>>
>> If we assume that we will never do register_shrinker and
>> unregister_shrinker on the same object in parallel then do we still
>> need to do msleep & synchronize_rcu() within mutex?
>
> Doing register_shrinker() and unregister_shrinker() on the same object
> in parallel is wrong. This mutex is to ensure that we do not need to
> worry about ->list.next field. synchronize_rcu() should not be slow.
> If you want to avoid msleep() with mutex held, you can also apply
>
>> > If you want parallel register_shrinker()/unregister_shrinker(), something like
>> > shown below on top of shown above will do it.
>
> change.

Thanks for the explanation. Can you post the patch for others to
review without parallel register/unregister and SHRINKER_PERMANENT (we
can add when we need them)? You can use the motivation for the patch I
mentioned in my patch instead.