linux-kernel - Re: [PATCH v2] mm, shrinker: make shrinker

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Date:   Fri, 10 Nov 2017 10:16:14 -0800
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Minchan Kim <minchan@...nel.org>,
        Huang Ying <ying.huang@...el.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Michal Hocko <mhocko@...nel.org>,
        Greg Thelen <gthelen@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] mm, shrinker: make shrinker_list lockless

On Thu, Nov 9, 2017 at 1:46 PM, Tetsuo Handa
<penguin-kernel@...ove.sakura.ne.jp> 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.