linux-kernel - Re: dst cache overflow

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Date:	Tue, 14 Aug 2007 20:00:15 +0200
From:	Tobias Diedrich <ranma+kernel@...edrich.de>
To:	Eric Dumazet <dada1@...mosbay.com>
Cc:	linux-net@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: dst cache overflow

Eric Dumazet wrote:

> Tobias Diedrich <ranma+kernel@...edrich.de> wrote:
> 
> > Hello,
> > 
> > I suspect I'm seeing a slow dst cache leakage on one of my servers.
> > The server in question (oni) regularly needs to be rebooted, because
> > it loses network connectivity. However, netconsole and syslog shows that the
> > machine is still running and the kernel complains about "dst cache
> > overflow".
> > 
> > I have since installed a monitoring script, which stores the output of
> > both "ip route ls cache | fgrep cache | wc -l" and the 'entries' value
> > of /proc/net/stat/rt_cache (as suggested in 
> > http://www.mail-archive.com/netdev@vger.kernel.org/msg02107.html)
> > and produces a nice rrd graph:
> > 
> > http://uguu.de/~ranma/route-month-oni.png
> > So entries is growing more or less constantly, while the number of
> > active routes (not visible on the graph due to being too small) is
> > relatively constant.
> > 
> > Comparing this to another host running the exact same kernel:
> > http://uguu.de/~ranma/route-month-ari.png
> > Here cached_routes and entries barely differ at all.
> > 
> > The funny thing is, both hosts are running the exact same kernel
> > and use more or less the same iptables rules.
> > 
> > So I'm not sure what would cause the dst cache to leak only on host
> > oni?
> > 
> 
> Could you send the result of these commands on oni and ari ?
> 
> ip route ls
> grep . /proc/sys/net/ipv4/route/*

Sure.

AFAICS the only visible difference is gc_thresh, which is probably
double the size on oni since oni has double the amount of memory
(512MB for oni vs. 256MB for ari).

Host oni:

# ip route ls output:
217.172.187.0/24 dev eth0  proto kernel  scope link  src 217.172.187.75 
default via 217.172.187.1 dev eth0 

# grep output:
/proc/sys/net/ipv4/route/error_burst:500
/proc/sys/net/ipv4/route/error_cost:100
/proc/sys/net/ipv4/route/gc_elasticity:8
/proc/sys/net/ipv4/route/gc_interval:60
/proc/sys/net/ipv4/route/gc_min_interval:0
/proc/sys/net/ipv4/route/gc_min_interval_ms:500
/proc/sys/net/ipv4/route/gc_thresh:4096
/proc/sys/net/ipv4/route/gc_timeout:300
/proc/sys/net/ipv4/route/max_delay:10
/proc/sys/net/ipv4/route/max_size:65536
/proc/sys/net/ipv4/route/min_adv_mss:256
/proc/sys/net/ipv4/route/min_delay:2
/proc/sys/net/ipv4/route/min_pmtu:552
/proc/sys/net/ipv4/route/mtu_expires:600
/proc/sys/net/ipv4/route/redirect_load:2
/proc/sys/net/ipv4/route/redirect_number:9
/proc/sys/net/ipv4/route/redirect_silence:2048
/proc/sys/net/ipv4/route/secret_interval:600

Host ari:

# ip route ls output:
217.160.215.0/24 dev eth0  proto kernel  scope link  src 217.160.215.119 
default via 217.160.215.1 dev eth0 

# grep output:
/proc/sys/net/ipv4/route/error_burst:500
/proc/sys/net/ipv4/route/error_cost:100
/proc/sys/net/ipv4/route/gc_elasticity:8
/proc/sys/net/ipv4/route/gc_interval:60
/proc/sys/net/ipv4/route/gc_min_interval:0
/proc/sys/net/ipv4/route/gc_min_interval_ms:500
/proc/sys/net/ipv4/route/gc_thresh:2048
/proc/sys/net/ipv4/route/gc_timeout:300
/proc/sys/net/ipv4/route/max_delay:10
/proc/sys/net/ipv4/route/max_size:32768
/proc/sys/net/ipv4/route/min_adv_mss:256
/proc/sys/net/ipv4/route/min_delay:2
/proc/sys/net/ipv4/route/min_pmtu:552
/proc/sys/net/ipv4/route/mtu_expires:600
/proc/sys/net/ipv4/route/redirect_load:2
/proc/sys/net/ipv4/route/redirect_number:9
/proc/sys/net/ipv4/route/redirect_silence:2048
/proc/sys/net/ipv4/route/secret_interval:600

-- 
Tobias						PGP: http://9ac7e0bc.uguu.de
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