linux-kernel - Re: [PATCH] epoll: account epitem and eppoll

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Message-ID: <20171005082118.a4ynfvnq4loyufge@dhcp22.suse.cz>
Date:   Thu, 5 Oct 2017 10:21:18 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Greg Thelen <gthelen@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>, linux-fsdevel@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] epoll: account epitem and eppoll_entry to kmemcg

On Wed 04-10-17 12:33:14, Shakeel Butt wrote:
> >
> > I am not objecting to the patch I would just like to understand the
> > runaway case. ep_insert seems to limit the maximum number of watches to
> > max_user_watches which should be ~4% of lowmem if I am following the
> > code properly. pwq_cache should be bound by the number of watches as
> > well, or am I misunderstanding the code?
> >
> 
> You are absolutely right that there is a per-user limit (~4% of total
> memory if no highmem) on these caches. I think it is too generous
> particularly in the scenario where jobs of multiple users are running
> on the system and the administrator is reducing cost by overcomitting
> the memory. This is unaccounted kernel memory and will not be
> considered by the oom-killer. I think by accounting it to kmemcg, for
> systems with kmem accounting enabled, we can provide better isolation
> between jobs of different users.

Thanks for the clarification. For some reason I didn't figure that the
limit is per user, even though the name suggests so.

-- 
Michal Hocko
SUSE Labs