On 09/03/2018 07:27 AM, Eugen Block wrote:
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?
I'm not entirely sure what you mean by "shut down an instance". Perhaps
this is what is leading to confusion. I consider "shutting down an
instance" to be stopping or suspending an instance.
As I mentioned below, shutdown instances consume memory from an
inventory management perspective. If you stop or suspend an instance on
your host, that instance is still consuming the same amount of memory in
the placement service. You will *not* be able to launch a new instance
on that same compute host *unless* your allocation ratio is >1.0.
Now, if by "shut down an instance", you actually mean "terminate an
instance" or possibly "shelve and then offload an instance", then that
is a different thing, and in both of *those* cases, resources are
released on the compute host.
Best,
-jay
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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