Manage user.slice and system.slice resource allocation through host inventory

[roamingengineer311]

To manage resource allocation for user.slice and system.slice on hypervisor hosts, it would be useful to provide a way to configure systemd slice resource limits directly through the deployment inventory.

The feature should be disabled by default:

resource_allocation: false

It can be enabled globally through inventory variables:

vars:
  resource_allocation: true

When resource_allocation is enabled, the following default resource limits should be applied to every hypervisor host:

user.slice:
  MemoryHigh: 10G
  MemoryMax: 12G
  CPUQuota: 800%

system.slice:
  MemoryHigh: 4G

These defaults should be overridable on a per-host basis through the inventory.

For example:

vars: 
  resource_allocation: true 

node: 
  hosts: 
    kvm01: 
      ansible_host: 10.1.1.100
      slices: 
        user.slice: 
          MemoryHigh: 8G 
          MemoryMax: 10G 
          CPUQuota: 1000% 
        system.slice: 
          MemoryHigh: 6G

[dann1]

For implementation, consider also the slice management this PR introduces.

[sk4zuzu]

@dann1 Yes the PR you mentioned was actually the only sane way I found to truly isolate and protect resources for Infra / DPDK from libvirt, otherwise it was all over the place.. (🤭).

[sk4zuzu]

There's also this #211 I want to fully refactor after we agree upon how to make resource isolation actually happen. 🤔