Varnish 2.1 + kswapd0 freak out

Ken Brownfield kb+varnish at
Sat May 22 00:30:30 CEST 2010

This happens when there is significant memory pressure (heavy network or block I/O exacerbates it) when you have swap disabled.  This is a long-standing kernel behavior issue, from my experience.  I've seen it with MySQL and other servers, in addition to Varnish.

That being said, perhaps Varnish is initiating a huge object expiry pass that's triggering this problem.  If you increase the cli_timeout, it may help prevent the child from being reaped, to probably dubious benefit.

Increasing /proc/sys/vm/min_free_kbytes (by 2-3x) may also help, but it's a dangerous beast.  I use 131072 for all of my Varnish instances, for this reason (16-64GB boxes).

You may also find that adding a few hundred meg of swap is the lesser of two evils.

Hope it helps,

On May 20, 2010, at 3:45 PM, Augusto Becciu wrote:

> We don't have swap enabled on these servers.

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