Hi,

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.
let's forget about the scheduler, I'll try to make my question a bit clearer.

Let's say I have a ratio of 1.0 on my hypervisor, and let it have 24 GB of RAM available, ignoring the OS for a moment. Now I launch 6 instances, each with a flavor requesting 4 GB of RAM, that would leave no space for further instances, right? Then I shutdown two instances (freeing 8 GB RAM) and create a new one with 8 GB of RAM, the compute node is full again (assuming all instances actually consume all of their RAM). Now I boot one of the shutdown instances again, the compute node would require additional 4 GB of RAM for that instance, and this would lead to OOM, isn't that correct? So a ratio of 1.0 would not prevent that from happening, would it?
Regards,
Eugen


Zitat von Jay Pipes <jaypi...@gmail.com>:

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

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