Re: [libvirt-users] starting a domain only when you have enough resources

On 26.01.2016 12:30, Andrei Perietanu wrote: > 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? There is one option I see, use -mem-prealloc. Either you can passthrough it onto qemu commandline [1] or use locked memoryBacking [2]. I advocate for the latter though. Not only it will allocate all the memory at qemu startup it will also lock it so it won't get swapped off. Michal 1: http://libvirt.org/drvqemu.html#qemucommand 2: http://libvirt.org/formatdomain.html#elementsMemoryBacking