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Date:   Tue, 3 Jul 2018 12:25:17 -0700
From:   Matthew Wilcox <willy@infradead.org>
To:     Shakeel Butt <shakeelb@google.com>
Cc:     Kirill Tkhai <ktkhai@virtuozzo.com>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Philippe Ombredanne <pombredanne@nexb.com>,
        stummala@codeaurora.org, gregkh@linuxfoundation.org,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Roman Gushchin <guro@fb.com>, mka@chromium.org,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        Chris Wilson <chris@chris-wilson.co.uk>, longman@redhat.com,
        Minchan Kim <minchan@kernel.org>,
        Huang Ying <ying.huang@intel.com>,
        Mel Gorman <mgorman@techsingularity.net>, jbacik@fb.com,
        Guenter Roeck <linux@roeck-us.net>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux MM <linux-mm@kvack.org>, lirongqing@baidu.com,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v8 03/17] mm: Assign id to every memcg-aware shrinker
Message-ID: <20180703192517.GA22738@bombadil.infradead.org>
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On Tue, Jul 03, 2018 at 12:19:35PM -0700, Shakeel Butt wrote:
> On Tue, Jul 3, 2018 at 12:13 PM Kirill Tkhai <ktkhai@virtuozzo.com> wrote:
> > > Do we really have so very many !memcg-aware shrinkers?
> > >
> > > $ git grep -w register_shrinker |wc
> > >      32     119    2221
> > > $ git grep -w register_shrinker_prepared |wc
> > >       4      13     268
> > > (that's an overstatement; one of those is the declaration, one the definition,
> > > and one an internal call, so we actually only have one caller of _prepared).
> > >
> > > So it looks to me like your average system has one shrinker per
> > > filesystem, one per graphics card, one per raid5 device, and a few
> > > miscellaneous.  I'd be shocked if anybody had more than 100 shrinkers
> > > registered on their laptop.
> > >
> > > I think we should err on the side of simiplicity and just have one IDR for
> > > every shrinker instead of playing games to solve a theoretical problem.
> >
> > It just a standard situation for the systems with many containers. Every mount
> > introduce a new shrinker to the system, so it's easy to see a system with
> > 100 or ever 1000 shrinkers. AFAIR, Shakeel said he also has the similar
> > configurations.
> >
> 
> I can say on our production systems, a couple thousand shrinkers is normal.

But how many are !memcg aware?  It sounds to me like almost all of the
shrinkers come through the sget_userns() caller, so the other shrinkers
are almost irrelevant.