file stoarage type

Matt Schurenko MSchurenko at
Thu Aug 18 18:33:39 CEST 2011

Thanks for answering my question Tollef. I was reading about the mmap system call in Linux last night so your answer makes some sense to me. :)

Could you be so kind as to answer another question? I am wondering if I should use malloc or file for the storage type. I have read that if your cache is small enough to remain mostly in memory it is best to use malloc, but if it will exceed the amount of physical RAM you have available that mmap performs better than relying on your system's use of swap space. Is this accurate?

Matt Schurenko
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-----Original Message-----
From: Tollef Fog Heen [mailto:tfheen at] 
Sent: August-17-11 11:19 PM
To: Matt Schurenko
Cc: varnish-misc at
Subject: Re: file stoarage type

]] Matt Schurenko 

| I've read all the documentation I can get my hands on and still don't
| understand how the file Storage Type works. What does "Storage for
| each object is allocated from an arena backed by a file." really mean?
| For example, if I specify a size of 40GB how much physical RAM will
| varnish attempt to use? Will it try to use all available RAM and, if
| there's no more available, then use the file?

The kernel manages the amount of physical memory to allocate as cache
for the file, Varnish does not try to manage that explicitly.  So, the
answer is «it depends».  (Varnish will use memory for threads and
various other data structures, but the cache contents itself will be
balanced between memory and disk by the kernel automatically.)

Tollef Fog Heen
Varnish Software
t: +47 21 98 92 64

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