starting a domain only when you have enough resources

[Andrei Perietanu <andrei.perietanu@xxxxxxxxxxxxxxx>]

Hi all, 

  

I am running KVM on a 3.18 kernel. The system runs and Atom processor with 2Gb RAM. 

Using KVM you obviously can over allocate your resources: say you have 4 guests each configured with 1GB ram. Running all four at the same time, depending on the workload, can crash the system - I get a kernel trace when this happens.

But let's consider a simpler case: one guest with 1.5 Gb RAM, ubuntu 14.03.

During the installation the system will again crash. 

The memory statistics (top or proc/meminfo) will show that the FreeMemory goes down to 12Mb when this happens - which kind of makes sense considering the host will require some RAM to run.

But the question is: does libvirt offer any way to prevent this from happening? 

Some way of not allowing the user to start a guest unless you have enough free memory. I know how much ram each guest has configured but that is not enough. I need to know how much the system has available, and just reading the free memory statistic does not help much since that is only a snapshot - when running a guest you can have 1gb free now, and 10 mb free 2 min later.

Any ideas?

Thanks,

Andrei

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