linux-kernel - Re: [PATCH v4 15/16] memcg: enable accounting for tty-related objects

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Date:   Wed, 28 Apr 2021 09:38:03 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Vasily Averin <vvs@...tuozzo.com>
Cc:     cgroups@...r.kernel.org, Michal Hocko <mhocko@...nel.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Roman Gushchin <guro@...com>,
        Jiri Slaby <jirislaby@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 15/16] memcg: enable accounting for tty-related objects

On Wed, Apr 28, 2021 at 09:54:16AM +0300, Vasily Averin wrote:
> At each login the user forces the kernel to create a new terminal and
> allocate up to ~1Kb memory for the tty-related structures.
> 
> By default it's allowed to create up to 4096 ptys with 1024 reserve for
> initial mount namespace only and the settings are controlled by host admin.
> 
> Though this default is not enough for hosters with thousands
> of containers per node. Host admin can be forced to increase it
> up to NR_UNIX98_PTY_MAX = 1<<20.
> 
> By default container is restricted by pty mount_opt.max = 1024,
> but admin inside container can change it via remount. As a result,
> one container can consume almost all allowed ptys
> and allocate up to 1Gb of unaccounted memory.
> 
> It is not enough per-se to trigger OOM on host, however anyway, it allows
> to significantly exceed the assigned memcg limit and leads to troubles
> on the over-committed node.
> 
> It makes sense to account for them to restrict the host's memory
> consumption from inside the memcg-limited container.
> 
> Signed-off-by: Vasily Averin <vvs@...tuozzo.com>

Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>