Mailing List Archive: [nova]

[nova]

Aug 30, 2018, 7:19 AM

Post #1 of 3 (753 views)

Hi *,

I posted my question in [1] a week ago, but no answer yet.

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.

Regards,
Eugen

[1]
https://ask.openstack.org/en/question/115812/nova-scheduler-when-are-filters-applied/

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Re: [nova] [ In reply to ]

jaypipes at gmail

Aug 30, 2018, 7:35 AM

Post #2 of 3 (753 views)

Permalink

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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Re: [nova] Nova-scheduler: when are filters applied? [ In reply to ]

eblock at nde

Aug 30, 2018, 7:54 AM

Post #3 of 3 (753 views)

Permalink

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@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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