varnish 2.1.5 memory and swap

[Hettwer, Marian]

Hi List,

I'm running varnish successfully in front of a high traffic website.
However, once in a while (every few weeks), my Nagios notifies me that one
of my varnish machines is about to run out of swap.


I can't get around Linux and swap usage.
So here is what I have:

A varnishd with 6GB malloc.
root at kvarnish46-1:~ # ps ax | grep varnish
21692 ? Ss 1:07 /usr/sbin/varnishd -P /var/run/varnishd.pid -a :80 -f
/etc/varnish/kvarnish.vcl -T 127.0.0.1:6082 -t 120 -h critbit -p
thread_pools 4 -p thread_pool_min 100 -p thread_pool_max 5000 -p
thread_pool_add_delay 2 -p session_linger 120 -p connect_timeout 4 -S
/etc/varnish/secret -s malloc,6G
21693 ? Sl 1709:15 /usr/sbin/varnishd -P /var/run/varnishd.pid -a :80 -f
/etc/varnish/kvarnish.vcl -T 127.0.0.1:6082 -t 120 -h critbit -p
thread_pools 4 -p thread_pool_min 100 -p thread_pool_max 5000 -p
thread_pool_add_delay 2 -p session_linger 120 -p connect_timeout 4 -S
/etc/varnish/secret -s malloc,6G
27134 pts/0 S+ 0:00 grep --color=auto varnish



On a machine with 8GB RAM and 1 GB swap.

root at kvarnish46-1:~ # free
             total       used       free     shared    buffers     cached
Mem:       8194928    8007964     186964          0      99988     144468
-/+ buffers/cache:    7763508     431420
Swap:      1052636     950848     101788

There is not running anything else. Apart from system cronjobs and sshd.

The machine is exclusive for running varnish.

Uname -a
Linux kvarnish46-1 2.6.35-mobile.de.lenny #1 SMP Tue Aug 17 17:57:04 CEST
2010 x86_64 GNU/Linux

It's a Debian 5.0.8.

Any hints or even better explanation what is going on here?
I thought about chaning the vm.swapiness parameter. But I'm not sure
whether this would do the trick. Or better: What it actually would change.

My best theory is, that varnish is using virtual memory and that the
memory management of linux is kinda stubbornly putting the pages into
swap, because varnish hasn't ask for them quite a while.
I really don't like my own theory... Yak!

Any help appreciated and thanks in advance,
Marian