From: Tejaswi Nadahalli
> I am running my Python origin-server on the same machine. It seems like
> the Python interpreter caused the OOM killer to kill Varnish. If that's
> the case, is there anything I can do prevent this from happening?
I've been meaning to write-up a blog entry regarding the OOM killer in Linux
(what a dumb idea) but in the mean time this should get you started.
The OOM Killer is there because Linux, by default in most distros, allocates
more memory than available (swap+ram) on the assumption that applications will
never need it (this is called overcommiting). Mostly this is true but when
it's not the oom_kill is called to free-up some memory so the kernel can keep
its promise. Usually it does a shit job (as you just noticed) and I hate it so
much.
One way to solve this is to tweak oom_kill so it doesn't kill varnish
processes. It's a bit cumbersome because you need to do that based on the PID,
which you only learn after the process has started, leaving room for some nifty
race conditions. Still, adding these to Varnish's init scripts should do what
you need - look up online for details.
The other way is to disable memory overcommit. Add to /etc/sysctl.conf:
# Disables memory overcommit
vm.overcommit_memory = 2
# Tweak to fool VM (read manual for setting above)
vm.overcommit_ratio = 100
# swap only if really needed
vm.swappiness = 10
and sudo /sbin/sysctl -e -p /etc/sysctl.conf
The problem with setting overcommit_memory to 2 is that the VM will not
allocate more memory than you have available (the actual rule is a function of
RAM, swap and overcommit_ratio, hence the tweak above).
This could be a problem for Varnish depending on the storage used. The file
storage will mmap the file, resulting in a VM size as large as the file. If
you don't have enough RAM the kernel will deny memory allocation and varnish
will fail to start. At this point you either buy more RAM or tweak your swap
size to account for greedy processes (ie.: processes that allocate a lot of
memory but never use it).
TL;DR: buy more memory; get rid of memory hungry scripts in your varnish box
Good luck.
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