Varnish virtual memory usage

Roi Avinoam roi at
Wed Oct 21 19:27:01 CEST 2009

I don't remember how long it took exactly, but it filled up rather quickly. Probably a couple of hours. I also noticed the LRU-moved stat was pretty constant all along, no large spikes towards the end of the swap. 

Anyways, it was WAY over 1GB, we managed to fill more around 6-7GB.

Just for kicks, I tried changing the storage to malloc, and limit it to 1GB, to see the difference. We have live traffic now, so I don't wanna run the load testing scripts, but we should hit the 1GB limit within a day or two.

-----Original Message-----
From: Kristian Lyngstol [mailto:kristian at] 
Sent: Wednesday, October 21, 2009 3:28 PM
To: Roi Avinoam
Cc: varnish-misc at
Subject: Re: Varnish virtual memory usage

On Wed, Oct 21, 2009 at 03:07:00PM +0200, Roi Avinoam wrote:
> Thanks for your reply.
> 1. What I did was create 100 simultaneous processes, and each process requested the same page (with 'curl'):
> 	a. Once with the exact same URL - which resulted in a 99.9% hit-ratio and VERY high performance on varnish.
> 	b. And once with a random key that changes the URL (something like 'index.php?rand=193837364'), thus forcing Varnish to hit the backend, and store the multiple objects in memory. 
> 	c. A combination of the two - in an attempt to maintain a 60-70% hit-ratio.
> What we saw is that the kernel simply filled all of the RAM *and* the swap until it crashed. 

When did it fill up and how fast?

> 2. I'm sorry, but I'm still confused about the mmaped file. If it's 
> limited to 1G, Varnish shouldn't use more than 1G of virtual memory, 
> correct? Or in our setup - 1G of RAM?

The -s parameter only applies to storage, which is to say that it's an approximiation and there will be some additional overhead which is not stored there, ie datastructures for threads, sessions, backends etc.

So with -s ..., 1G, you should expect a little bit over 1GB, but not nearly as much as you describe.

Kristian Lyngstøl
Redpill Linpro AS
Tlf: +47 21544179
Mob: +47 99014497

More information about the varnish-misc mailing list