Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Fri, 18 Dec 2020 12:09:28 +1100
From:   Dave Chinner <david@fromorbit.com>
To:     Yang Shi <shy828301@gmail.com>
Cc:     Roman Gushchin <guro@fb.com>, Kirill Tkhai <ktkhai@virtuozzo.com>,
        Shakeel Butt <shakeelb@google.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@suse.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux MM <linux-mm@kvack.org>,
        Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [v2 PATCH 7/9] mm: vmscan: don't need allocate
 shrinker->nr_deferred for memcg aware shrinkers
Message-ID: <20201218010928.GB1199812@dread.disaster.area>
References: <20201214223722.232537-1-shy828301@gmail.com>
 <20201214223722.232537-8-shy828301@gmail.com>
 <20201215030528.GN3913616@dread.disaster.area>
 <CAHbLzkoOcTuidghuR_pLsE4RX_6DiwXW+k2EQRJxrB6BDqhvBA@mail.gmail.com>
 <CAHbLzkoWco5gq8tuxbTsfpTF3GPUQLn9uNUTy1nUNwKGVPonmg@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAHbLzkoWco5gq8tuxbTsfpTF3GPUQLn9uNUTy1nUNwKGVPonmg@mail.gmail.com>
Precedence: bulk

On Thu, Dec 17, 2020 at 04:56:48PM -0800, Yang Shi wrote:
> On Tue, Dec 15, 2020 at 3:07 PM Yang Shi <shy828301@gmail.com> wrote:
> > > This guarantees that only the shrinker instances taht have a
> > > correctly set up memcg attached to them will have the
> > > SHRINKER_MEMCG_AWARE flag set. Hence in all the rest of the shrinker
> > > code, we only ever need to check for SHRINKER_MEMCG_AWARE to
> > > determine what we should do....
> >
> > Thanks. I see your point. We could move the memcg specific details
> > into prealloc_memcg_shrinker().
> >
> > It seems we have to acquire shrinker_rwsem before we check and modify
> > SHIRNKER_MEMCG_AWARE bit if we may clear it.
> 
> Hi Dave,
> 
> Is it possible that shrinker register races with shrinker unregister?
> It seems impossible to me by a quick visual code inspection. But I'm
> not a VFS expert so I'm not quite sure.

Uh, if you have a shrinker racing to register and unregister, you've
got a major bug in your object initialisation/teardown code. i.e.
calling reagister/unregister at the same time for the same shrinker
is a bug, pure and simple.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com