Sorry, the release was Mitaka, so this is a duplicate bug. I've changed
status to Invalid.
** Changed in: nova
Status: New => Invalid
--
You received this bug notification because you are a member of Yahoo!
Engineering Team, which is subscribed to OpenStack Compute (nova).
https://bugs.launchpad.net/bugs/1736224
Title:
ram_allocation_ratio > 1 causes RAMFIlter to incorrectly decide on
ability so spawn instance
Status in OpenStack Compute (nova):
Invalid
Bug description:
The problem is inside this function -
https://github.com/openstack/nova/blob/master/nova/scheduler/filters/ram_filter.py#L33
Probably related to https://bugs.launchpad.net/nova/+bug/1635367
The problem is that RAMFilter calculations do not take into account VM
RAM subscription. This causes scheduler to try spawning VMs on hosts
which a fully oversubscribed while still have some physical free RAM -
this is possible due to KSM for example.
Consider this scenario:
ram_allocation_ratio = 1.5
Some compute host has 10GB physical RAM and 15 1GB VMs already spawned on it.
At the same time, there is still 2GB free physical RAM on the host, as seen
in "free -m" and in nova hypervisor-show.
A new VM is scheduled and RAMFilter is executed:
requested_ram = spec_obj.memory_mb = 1GB
free_ram_mb = host_state.free_ram_mb = 2GB # this is actual free RAM on a
host, which does not properly reflect VM subscription
total_usable_ram_mb = host_state.total_usable_ram_mb = 10GB # host has 10GB
RAM total
Then the main check which is performed is:
memory_mb_limit = total_usable_ram_mb * ram_allocation_ratio = 15GB
used_ram_mb = total_usable_ram_mb - free_ram_mb = 10 - 2 = 8GB
usable_ram = memory_mb_limit - used_ram_mb = 15 - 8 = 7GB # incorrect
assumption that host has 7GB usable RAM left
Unless I have some incorrect understanding, the logic here is broken.
At first I tried to make up a quick fix, but then realized the VM
subscription RAM value (sum of RAM of all VMs scheduled on a host) is not
present in this code so proper calculation cannot be done. It may be available
inside host_state object, I have not checked yet.
To manage notifications about this bug go to:
https://bugs.launchpad.net/nova/+bug/1736224/+subscriptions
--
Mailing list: https://launchpad.net/~yahoo-eng-team
Post to : [email protected]
Unsubscribe : https://launchpad.net/~yahoo-eng-team
More help : https://help.launchpad.net/ListHelp
