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Date:   Wed, 6 Dec 2017 13:43:21 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>
Cc:     axboe@...nel.dk, bcrl@...ck.org, tj@...nel.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-aio@...ck.org, jmoyer@...hat.com
Subject: Re: [PATCH] aio: Add memcg accounting of user used data

On Wed 06-12-17 15:36:56, Kirill Tkhai wrote:
> On 06.12.2017 15:23, Michal Hocko wrote:
> > On Tue 05-12-17 13:00:54, Kirill Tkhai wrote:
> > [...]
> >> This meets the problem in case of many containers
> >> are used on the hardware node. Since aio_max_nr is
> >> a global limit, any container may occupy the whole
> >> available aio requests, and to deprive others the
> >> possibility to use aio at all. The situation may
> >> happen because of evil intentions of the container's
> >> user or because of the program error, when the user
> >> makes this occasionally
> > 
> > I am sorry to beat more on this but finally got around to
> > http://lkml.kernel.org/r/17b22d53-ad3d-1ba8-854f-fc2a43d86c44@virtuozzo.com
> > and read the above paragraph once again. I can see how accounting to
> > a memcg helps to reduce the memory footprint but I fail to see how it
> > helps the above scenario. Could you clarify wow you set up a limit to
> > prevent anybody from DoSing other containers by depleting aio_max_nr?
> The memcg limit allows to increase aio_max_nr and the accounting guarantees
> container can't exceed the limit. You may configure the limit and aio_max_nr
> in the way, all containers requests in sum never reach aio_max_nr.

So you are essentially saying that you make aio_max_nr unlimited and
rely on the memory consumption tracking by memcg, right? Are there any
downsides (e.g. clog the AIO subsytem)?

Please make sure that all this in the changelog.
-- 
Michal Hocko
SUSE Labs

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