[Openstack-operators] Instance memory overhead
leongmzlist at gmail.com
Tue Jun 23 15:44:46 UTC 2015
My instances are using much more memory that expected. The amount free
memory (free + cached) is under 3G on my servers even though the compute
nodes are configured to reserve 32G.
Here's my setup:
Release: Ice House
Server mem: 256G
Qemu version: 2.0.0+dfsg-2ubuntu1.1
Networking: Contrail 1.20
Block storage: Ceph 0.80.7
Hypervisor OS: Ubuntu 12.04
memory over-provisioning is disabled
kernel version: 3.11.0-26-generic
reserved_host_memory_mb = 32768
Info on instances:
- root volume is file backed (qcow2) on the hypervisor local storage
- each instance has a rbd volume mounted from Ceph
- no swap file/partition
I've confirmed, via nova-compute.log, that nova is respecting the
reserved_host_memory_mb directive and is not over-provisioning. On some
hypervisors, nova-compute says there's 4GB available for use even though
the OS has less that 4G left (free +cached)!
I've also summed up the memory from /etc/libvir/qemu/*.xml files and the
total looks good.
Each hypervisor hosts about 45-50 instances.
Is there good way to calculate the actual usage of each QEMU process?
PS: I've tried free, summing up RSS, and smem but none of them can tell me
where's the missing mem.
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