diff --git a/nova_powervm/tests/virt/powervm/test_driver.py b/nova_powervm/tests/virt/powervm/test_driver.py
index 7fc10713..98f1aca8 100644
--- a/nova_powervm/tests/virt/powervm/test_driver.py
+++ b/nova_powervm/tests/virt/powervm/test_driver.py
@@ -1596,7 +1596,7 @@ class TestPowerVMDriver(test.NoDBTestCase):
             self.assertIsNotNone(value)
 
     @contextlib.contextmanager
-    def _update_provider_tree(self):
+    def _update_provider_tree(self, allocations=None):
         """Host resource dict gets converted properly to provider tree inv."""
 
         with mock.patch('nova_powervm.virt.powervm.host.'
@@ -1632,7 +1632,8 @@ class TestPowerVMDriver(test.NoDBTestCase):
             ptree.new_root('compute_host', uuids.cn)
             # Let the caller muck with these
             yield ptree, exp_inv
-            self.drv.update_provider_tree(ptree, 'compute_host')
+            self.drv.update_provider_tree(ptree, 'compute_host',
+                                          allocations=allocations)
             self.assertEqual(exp_inv, ptree.data('compute_host').inventory)
             mock_bhrfm.assert_called_once_with('host_wrapper')
 
@@ -1642,6 +1643,10 @@ class TestPowerVMDriver(test.NoDBTestCase):
         with self._update_provider_tree():
             pass
 
+    def test_update_provider_tree_ignore_allocations(self):
+        with self._update_provider_tree(allocations="This is ignored"):
+            pass
+
     def test_update_provider_tree_conf_overrides(self):
         # Non-default CONF values for allocation ratios and reserved.
         self.flags(cpu_allocation_ratio=12.3,
diff --git a/nova_powervm/virt/powervm/driver.py b/nova_powervm/virt/powervm/driver.py
index a6c88570..c642ff51 100644
--- a/nova_powervm/virt/powervm/driver.py
+++ b/nova_powervm/virt/powervm/driver.py
@@ -987,7 +987,7 @@ class PowerVMDriver(driver.ComputeDriver):
 
         return data
 
-    def update_provider_tree(self, provider_tree, nodename):
+    def update_provider_tree(self, provider_tree, nodename, allocations=None):
         """Update a ProviderTree with current provider and inventory data.
 
         :param nova.compute.provider_tree.ProviderTree provider_tree:
@@ -1001,6 +1001,7 @@ class PowerVMDriver(driver.ComputeDriver):
             String name of the compute node (i.e.
             ComputeNode.hypervisor_hostname) for which the caller is requesting
             updated provider information.
+        :param allocations: Currently ignored by this driver.
         """
         # Get (legacy) resource information. Same as get_available_resource,
         # but we don't need to refresh self.host_wrapper as it was *just*
@@ -1017,8 +1018,7 @@ class PowerVMDriver(driver.ComputeDriver):
         mem_alloc_ratio = CONF.ram_allocation_ratio or 1.5
         mem_reserved = CONF.reserved_host_memory_mb
         disk_alloc_ratio = CONF.disk_allocation_ratio or 1.0
-        disk_reserved = compute_utils.convert_mb_to_ceil_gb(
-            CONF.reserved_host_disk_mb)
+        disk_reserved = self._get_reserved_host_disk_gb_from_config()
 
         inventory = {
             rc_fields.ResourceClass.VCPU: {