Pods Cannot allocate memory, even with memory_over_commit_ratio set 10.0

[webteam-app]

Bug originally filed by jog at https://bugs.launchpad.net/bugs/1831134

Expected to compose a pod VM with 4GB of memory on a host with 6GB of total physical memory when memory_over_commit_ratio is set to 10.

ubuntu@infra1:~$ maas root pod compose 10 hostname=juju-1 cores=1 memory=4096 storage=20
Unable to compose machine because: Failed talking to pod: Unable to compose juju-1: error: Failed to start domain juju-1
error: internal error: qemu unexpectedly closed the monitor: 2019-05-30T17:08:05.182033Z qemu-system- x86_64: -drive file=/var/lib/virt/images/13f6f8e3-681c-4de0-9981-a2a3856d56cc,format=raw,if=none,id=d rive-virtio-disk0,serial=13f6f8e3-681c-4de0-9981-a2a3856d56cc: 'serial' is deprecated, please use the corresponding option of '-device' instead
2019-05-30T17:08:05.183561Z qemu-system-x86_64: warning: host doesn't support requested feature: CPUI D.80000001H:ECX.svm [bit 2]
2019-05-30T17:08:05.186659Z qemu-system-x86_64: cannot set up guest memory 'pc.ram': Cannot allocate memory

ubuntu@infra1:~$ lsb_release -rd
Description: Ubuntu 18.04.2 LTS
Release: 18.04

ii maas-cli 2.5.3-7533-g65952b418-0ubuntu118.04.1 all MAAS client and command-line interface
ii maas-common 2.5.3-7533-g65952b418-0ubuntu118.04.1 all MAAS server common files
ii maas-dhcp 2.5.3-7533-g65952b418-0ubuntu118.04.1 all MAAS DHCP server
ii maas-proxy 2.5.3-7533-g65952b418-0ubuntu118.04.1 all MAAS Caching Proxy
ii maas-rack-controller 2.5.3-7533-g65952b418-0ubuntu118.04.1 all Rack Controller for MAAS
ii maas-region-api 2.5.3-7533-g65952b418-0ubuntu118.04.1 all Region controller API service for MAAS
ii maas-region-controller 2.5.3-7533-g65952b418-0ubuntu118.04.1 all Region Controller for MAAS
ii python3-django-maas 2.5.3-7533-g65952b418-0ubuntu118.04.1 all MAAS server Django web framework (Python 3)
ii python3-maas-client 2.5.3-7533-g65952b418-0ubuntu118.04.1 all MAAS python API client (Python 3)
ii python3-maas-provisioningserver 2.5.3-7533-g65952b418-0ubuntu118.04.1 all MAAS server provisioning libraries (Python 3)

[Caleb-Ellis]

Latest is that we should show a warning that qemu needs a minimum amount of space. How to determine when to show that warning is TBD