+++ This bug was initially created as a clone of Bug #2043588 +++
The parent bug is used to discuss the implementation of a feature that would automate the best we can the handling of hugepages in OSP18

This bug will be used to document a procedure to mount the hugepages folders on the compute nodes during firstboot.

Nova actually supports the handling of multiple pagesizes. 

This is how it can be done [1] using firstboot.

It's important to note that pre-deployed nodes are probably not running the firstboot templates so it might fall on the operator's shoulder to run something similar during their node provisioning process.

It's also important to note that these hugepage mounts need to be passed to the nova_compute and nova_libvirt containers. In this case, we create them under /dev which is automatically bindmounted to these containers, but if operators are choosing another destination, they need to make sure that it's passed to the containers as well.

Here's a quick summary of what happens with this template:
- We mask the default dev-hugepages.mount systemd unit file as we want to create new mounts using the pagesize.
- We make sure that the folders are created beforehand
- We create systemd mount units for each pagesizes
- After the first loop, we need to systemd daemon-reload to include these newly created units
- Finally, we start each one of these mounts

[1]
~~~
(undercloud) [stack@undercloud-0 ~]$ cat 16.2_deployment_files/hugepages.yaml
heat_template_version: queens

description: >
  Hugepages configuration

resources:
  userdata:
    type: OS::Heat::MultipartMime
    properties:
      parts:
      - config: {get_resource: hugepages_config}

  hugepages_config:
    type: OS::Heat::SoftwareConfig
    properties:
      config: |
        #!/bin/bash
        systemctl mask dev-hugepages.mount || true
        for pagesize in 2M 1G;do
          if ! [ -d "/dev/hugepages${pagesize}" ]; then
            mkdir -p "/dev/hugepages${pagesize}"
            cat << EOF > /etc/systemd/system/dev-hugepages${pagesize}.mount
        [Unit]
        Description=${pagesize} Huge Pages File System
        Documentation=https://www.kernel.org/doc/Documentation/vm/hugetlbpage.txt
        Documentation=https://www.freedesktop.org/wiki/Software/systemd/APIFileSystems
        DefaultDependencies=no
        Before=sysinit.target
        ConditionPathExists=/sys/kernel/mm/hugepages
        ConditionCapability=CAP_SYS_ADMIN
        ConditionVirtualization=!private-users
        
        [Mount]
        What=hugetlbfs
        Where=/dev/hugepages${pagesize}
        Type=hugetlbfs
        Options=pagesize=${pagesize}
        EOF
          fi
        done
        systemctl daemon-reload
        for pagesize in 2M 1G;do
          systemctl start dev-hugepages${pagesize}.mount
        done

outputs:
  OS::stack_id:
    value: {get_resource: userdata}

(undercloud) [stack@undercloud-0 ~]$ cat 16.2_deployment_files/firstboot.yaml
resource_registry:
  OS::TripleO::ComputeHugepage::NodeUserData: ./hugepages.yaml
~~~