RFE : If DVR is enabled increase reserved_host_memory_mb

[Joe Talerico]

If DVR is enabled, each compute node will have extra services running that eat up memory. It is important to properly set the `reserved_host_memory_mb` so that we account for this.

Due to : https://bugs.launchpad.net/neutron/+bug/1524916

This is a very large problem, with 50 Routers we can see upwards of 1GB of memory consumption.

My suggestion would be to increase the default 2GB if we ship with DVR to 5GB, however this will only support ~150 routers.

[Assaf Muller (amuller)]

When you're talking about 150 routers you're also saying that the node runs at least 150 VMs and that each VM belongs to a different network. I think that that's a very specific use case. Typically you have large amount of VMs in a network, and 1 router per network, therefor many VMs per router per host, so you'd end up hitting the VM density limit before you hit any bottleneck with routers. That being said, any cloud that has aggressive multi tenancy such as public clouds is hit by this issue severely.

[Joe Talerico (jtaleric)]

Currently we only have 2GB, are you suggesting this should suffice?

[Joe Talerico (jtaleric)]

Currently we only have 2GB _reserved_ for the hypervisor services (outside of guests), are you suggesting this should suffice?

[Steven Hardy (shardy)]

Sounds like we need some conditional logic to increase the default when DVR is enabled, and possibly expose parameters that make each default easy to configure as it doesn't sounds like any single value will suit all environments.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/382594
Committed: https://git.openstack.org/cgit/openstack/tripleo-heat-templates/commit/?id=eec4587bc77de49acdae29a86c9e197cb3b194db
Submitter: Jenkins
Branch: master

commit eec4587bc77de49acdae29a86c9e197cb3b194db
Author: Brent Eagles <email address hidden>
Date: Wed Oct 5 15:36:00 2016 -0230

    Increase reserved memory for computes when enabling DVR

    This patch adds an example increased value for NovaReservedHostMemory
    and some documentation around tuning this value when DVR is enabled.

    Closes-Bug: #1630583

    Change-Id: I2718d72d307a1c90061606e5f36c96f964cd2fb5

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/tripleo-heat-templates 6.0.0.0b2 development milestone.