roles/common: Install generic OOM configuration

- Allow killing of any cgroup if swap is about to run out. When swap is
  at least 90% full, oomd will kill a cgroup, tending to kill the cgroup
  with the highest swap usage.
- Allow killing cgroups of logged in users under severe memory pressure.
  When a cgroup is stalled waiting for memory at least 60% of the time,
  for at least 30 seconds, oomd will attempt to kill it or one of its
  descendant cgroups.

roles/common/files/oomd-override_-.slice.conf

+[Slice]
+ManagedOOMSwap=kill

roles/common/files/oomd-override_user@.service.conf

+[Service]
+ManagedOOMMemoryPressure=kill
+ManagedOOMMemoryPressureLimit=60%

roles/common/tasks/main.yml

@@ -103,6 +103,20 @@
   command: systemd-tmpfiles --create
   when: zramtmpfiles.changed
 
+- name: create drop-in directories for oomd
+  file: path=/etc/systemd/system/{{ item }}.d state=directory owner=root group=root mode=0755
+  with_items:
+    - "-.slice"
+    - user@.service
+
+- name: install drop-in snippets for oomd
+  copy: src=oomd-override_{{ item }}.conf dest=/etc/systemd/system/{{ item }}.d/override.conf owner=root group=root mode=0644
+  with_items:
+    - "-.slice"
+    - user@.service
+  notify:
+    - systemd daemon-reload
+
 - name: start systemd-oomd
   service: name=systemd-oomd state=started enabled=yes