CellsV1: Expire reservations in cells manager

Normally reservations are expired by a periodic task in nova-scheduler.
In a cells deployment quotas are usually enabled only on the api-level
cell. This uses a separate DB from the scheduler, so any reservations
on the top level never get expired.

This change adds the same periodic task to the cells manager so
reservations at all levels have a chance to be expired. The task is
disabled by default and can be turned on with the
CONF.cells.expire_reservations option.

Change-Id: I340e7ff6262a5007e2699217e1012dec9038c03b

nova/cells/manager.py

@@ -38,11 +38,13 @@
 from nova import objects
 from nova.objects import base as base_obj
 from nova.objects import instance as instance_obj
+from nova import quota
 
 
 CONF = nova.conf.CONF
 
 LOG = logging.getLogger(__name__)
+QUOTAS = quota.QUOTAS
 
 
 class CellsManager(manager.Manager):
@@ -112,6 +114,11 @@ def _update_our_parents(self, ctxt):
         self.msg_runner.tell_parents_our_capabilities(ctxt)
         self.msg_runner.tell_parents_our_capacities(ctxt)
 
+    @periodic_task.periodic_task
+    def _expire_reservations(self, context):
+        if CONF.cells.expire_reservations:
+            QUOTAS.expire(context)
+
     @periodic_task.periodic_task
     def _heal_instances(self, ctxt):
         """Periodic task to send updates for a number of instances to

nova/conf/cells.py

@@ -431,7 +431,11 @@
 
 * This value is used with the ``instance_updated_at_threshold``
   value in a periodic task run.
-""")
+"""),
+        cfg.BoolOpt("expire_reservations",
+                default=False,
+                help="If True, enable the periodic task for reservation "
+                "expiry."),
 ]
 
 cell_messaging_opts = [