netdev - Re: [PATCH net-next] ipv6/route: inherit max

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Message-ID: <20200520172417.4m7pyalpftdd2xrm@wittgenstein>
Date:   Wed, 20 May 2020 19:24:17 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     David Ahern <dsahern@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] ipv6/route: inherit max_sizes from current netns

On Wed, May 20, 2020 at 10:54:21AM -0600, David Ahern wrote:
> On 5/20/20 8:58 AM, Christian Brauner wrote:
> > During NorthSec (cf. [1]) a very large number of unprivileged
> > containers and nested containers are run during the competition to
> > provide a safe environment for the various teams during the event. Every
> > year a range of feature requests or bug reports come out of this and
> > this year's no different.
> > One of the containers was running a simple VPN server. There were about
> > 1.5k users connected to this VPN over ipv6 and the container was setup
> > with about 100 custom routing tables when it hit the max_sizes routing
> > limit. After this no new connections could be established anymore,
> > pinging didn't work anymore; you get the idea.
> > 
> 
> should have been addressed by:
> 
> commit d8882935fcae28bceb5f6f56f09cded8d36d85e6
> Author: Eric Dumazet <edumazet@...gle.com>
> Date:   Fri May 8 07:34:14 2020 -0700
>     ipv6: use DST_NOCOUNT in ip6_rt_pcpu_alloc()
>     We currently have to adjust ipv6 route gc_thresh/max_size depending
>     on number of cpus on a server, this makes very little sense.
> 
> 
> Did your tests include this patch?

No, it's also pretty hard to trigger. The conference was pretty good for
this.
I tested on top of rc6. I'm probably missing the big picture here, could
you briefy explain how this commit fixes the problem we ran into?

Thanks!
Christian