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

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Message-Id: <201711100646.IJH39597.HOtMLJVSFOQFOF@I-love.SAKURA.ne.jp>
Date:   Fri, 10 Nov 2017 06:46:19 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     shakeelb@...gle.com
Cc:     minchan@...nel.org, ying.huang@...el.com,
        mgorman@...hsingularity.net, vdavydov.dev@...il.com,
        mhocko@...nel.org, gthelen@...gle.com, hannes@...xchg.org,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm, shrinker: make shrinker_list lockless

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.