Host machine out of memory with QEMU/KVM 0.14
 

Hi,

I'm running KVM with libvirt for 2 years now. But I have a strange issue since a few months. The host machine runs out of memory and swap which causes kernel panic. My host machine (Ubuntu 10.10 x64) has 8gb memory and 2gb swap. I run 3 guests on this machine with the following memory settings:

- Guest 1: max and current usage: 2gb.
- Guest 2: max and current usage: 2gb.
- Guest 3: max 3gb and current usage: 2gb.

Total max. usage by guest: 7gb.

KVM/Libvirt version info
Compiled against library: libvir 0.9.0
Using library: libvir 0.9.0
Using API: QEMU 0.9.0
Running hypervisor: QEMU 0.14.0

When all guests are under high load the systeem may run out of memory (once or twice a month). I checked the memory usage from time to time: the KVM the process of Guest 3 uses more than 3gb (4.1gb is the max. I have seen). How is this possible?

Already thanks for your help and time.

Best regards,
Sander

The actual memory usage for each VM is slightly larger than the requested size. qemu-kvm VMs run about 20-25 percent more memory than the requested size on my systems. Reduce the amount of memory for each VM using that formula and that should solve the memory over commit issue.

Thanks for your reply.

I have lowered the max. total memory usage to 6gb (on a machine with 8gb RAM and 2gb swap). I will update this thread when I have the issue again.

have you tried to use KSM or balooning?