netdev - Re: IPv6 routing table max_size badly dimensioned compared to IPv4

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Message-ID: <20140227205010.GB27495@order.stressinduktion.org>
Date:	Thu, 27 Feb 2014 21:50:10 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	bert hubert <bert.hubert@...herlabs.nl>, netdev@...r.kernel.org
Subject: Re: IPv6 routing table max_size badly dimensioned compared to IPv4

On Thu, Feb 27, 2014 at 12:23:03PM -0800, Eric Dumazet wrote:
> > > What kernel version do you use ?
> > > 
> > > I thought this was already solved.
> > > 
> > > Commit 957c665f37007de93ccbe45902a23143724170d0 is in linux 3.0
> > > ("ipv6: Don't put artificial limit on routing table size.")
> > 
> > The problem with DNS is that just for the DNS/UDP ping-pong we clone a
> > rt6_info and reinsert it back into the fib.
> > 
> > DST_NOCOUNT logic only ensures we can still insert new routes from user space
> > while the maximum number of routes is reached in the routing table. In case
> > the ipv6 fib is under heavy load it does not help with performance.
> > 
> > We might think about raising this limit a bit. Number of IPv6 routing entries
> > in global routing table already passed 4096. Maybe some heuristic which scales
> > this value according to available memory?
> 
> 
> Well, if we attach one dst per packet, it seems we already have a limit
> of number of packets on the host (qdisc limits + packets on TX ring
> buffers)
> 
> So DST_NOCOUNT should be used in this case. I thought David patch
> was already doing this.

We store those routes back into the routing table, so we must have a way to
count them and trigger gc at some point.

Greetings,

  Hannes

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