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


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?

Regards,
Eugen


Zitat von Jay Pipes <jaypipes at gmail.com>:

> On 08/30/2018 10:19 AM, Eugen Block wrote:
>> When does Nova apply its filters (Ram, CPU, etc.)?
>> Of course at instance creation and (live-)migration of existing  
>> instances. But what about existing instances that have been  
>> shutdown and in the meantime more instances on the same hypervisor  
>> have been launched?
>>
>> When you start one of the pre-existing instances and even with RAM  
>> overcommitment you can end up with an OOM-Killer resulting in  
>> forceful shutdowns if you reach the limits. Is there something I've  
>> been missing or maybe a bad configuration of my scheduler filters?  
>> Or is it the admin's task to keep an eye on the load?
>>
>> I'd appreciate any insights or pointers to something I've missed.
>
> 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.
>
> Best,
> -jay
>
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