Add support for using a tmpfs for Cinder image conversion

This can improve performance of image format conversion and encryption, if
sufficient memory is available on the cinder-volume host.

Closes-Bug: #1897276

Change-Id: I4ca1c4db7b66fdfc6bb873aad2570234f3882d81

ansible/roles/cinder/defaults/main.yml

@@ -38,6 +38,7 @@ cinder_services:
     image: "{{ cinder_volume_image_full }}"
     privileged: True
     ipc_mode: "host"
+    tmpfs: "{{ cinder_volume_tmpfs }}"
     volumes: "{{ cinder_volume_default_volumes + cinder_volume_extra_volumes }}"
     dimensions: "{{ cinder_volume_dimensions }}"
   cinder-backup:
@@ -125,6 +126,12 @@ cinder_backup_extra_volumes: "{{ cinder_extra_volumes }}"
 cinder_scheduler_extra_volumes: "{{ cinder_extra_volumes }}"
 cinder_volume_extra_volumes: "{{ cinder_extra_volumes }}"
 
+cinder_volume_tmpfs:
+  - "{% if cinder_enable_conversion_tmpfs | bool %}/var/lib/cinder/conversion{% endif %}"
+
+# If true, use a tmpfs mount for the Cinder image conversion directory.
+cinder_enable_conversion_tmpfs: false
+
 ####################
 # OpenStack
 ####################

ansible/roles/cinder/handlers/main.yml

@@ -41,6 +41,7 @@
     image: "{{ service.image }}"
     privileged: "{{ service.privileged | default(False) }}"
     ipc_mode: "{{ service.ipc_mode | default('') }}"
+    tmpfs: "{{ service.tmpfs | default(omit) }}"
     volumes: "{{ service.volumes | reject('equalto', '') | list }}"
     dimensions: "{{ service.dimensions }}"
   when:

ansible/roles/cinder/tasks/check-containers.yml

@@ -6,6 +6,7 @@
     common_options: "{{ docker_common_options }}"
     name: "{{ item.value.container_name }}"
     image: "{{ item.value.image }}"
+    tmpfs: "{{ item.value.tmpfs | default(omit) }}"
     volumes: "{{ item.value.volumes | reject('equalto', '') | list }}"
     dimensions: "{{ item.value.dimensions }}"
     privileged: "{{ item.value.privileged | default(False) }}"

releasenotes/notes/cinder-conversion-tmpfs-94e2ed1de5d9ea06.yaml

+---
+features:
+  - |
+    Adds support for using a ``tmpfs`` mount for the image conversion directory
+    of the ``cinder_volume`` container. This is disabled by default, but may be
+    enabled by setting ``cinder_enable_conversion_tmpfs`` to ``true``.