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[Openstack] [nova] Nova-scheduler: when are filters applied?


On 08/30/2018 10:54 AM, Eugen Block wrote:
> Hi Jay,
> 
>> You need to set your ram_allocation_ratio nova.CONF option to 1.0 if 
>> you're running into OOM issues. This will prevent overcommit of memory 
>> on your compute nodes.
> 
> I understand that, the overcommitment works quite well most of the time.
> 
> It just has been an issue twice when I booted an instance that had been 
> shutdown a while ago. In the meantime there were new instances created 
> on that hypervisor, and this old instance caused the OOM.
> 
> I would expect that with a ratio of 1.0 I would experience the same 
> issue, wouldn't I? As far as I understand the scheduler only checks at 
> instance creation, not when booting existing instances. Is that a 
> correct assumption?

To echo what cfriesen said, if you set your allocation ratio to 1.0, the 
system will not overcommit memory. Shut down instances consume memory 
from an inventory management perspective. If you don't want any danger 
of an instance causing an OOM, you must set you ram_allocation_ratio to 1.0.

The scheduler doesn't really have anything to do with this.

Best,
-jay