Correct memory validation for live migration

Since live migration has been moved to the conductor, there was no
possibility for the conductor to verify if the destination had
enough RAM just because it didn't know the allocation ratios given
by the scheduler.

Now that ComputeNodes provide a ram_allocation_field, we can fix
that check and provide the same validation than RAMFilter to make
sure that the destination is good.

Closes-Bug: #1451831
Closes-Bug: #1214943

Change-Id: Ie6c768fc915553da73160ea51961078bfbacec77

Author: sbauza

nova/conductor/tasks/live_migrate.py

@@ -110,9 +110,17 @@ def _check_destination_is_not_source(self):
                     instance_id=self.instance.uuid, host=self.destination)
 
     def _check_destination_has_enough_memory(self):
-        avail = self._get_compute_info(self.destination)['free_ram_mb']
+        compute = self._get_compute_info(self.destination)
+        free_ram_mb = compute.free_ram_mb
+        total_ram_mb = compute.memory_mb
         mem_inst = self.instance.memory_mb
+        # NOTE(sbauza): Now the ComputeNode object reports an allocation ratio
+        # that can be provided by the compute_node if new or by the controller
+        ram_ratio = compute.ram_allocation_ratio
 
+        # NOTE(sbauza): Mimic the RAMFilter logic in order to have the same
+        # ram validation
+        avail = total_ram_mb * ram_ratio - (total_ram_mb - free_ram_mb)
         if not mem_inst or avail <= mem_inst:
             instance_uuid = self.instance.uuid
             dest = self.destination

nova/tests/unit/conductor/tasks/test_live_migrate.py

@@ -150,11 +150,13 @@ def test_check_requested_destination(self):
         objects.Service.get_by_compute_host(
             self.context, self.destination).AndReturn("service")
         self.task.servicegroup_api.service_is_up("service").AndReturn(True)
-        hypervisor_details = {
-            "hypervisor_type": "a",
-            "hypervisor_version": 6.1,
-            "free_ram_mb": 513
-        }
+        hypervisor_details = objects.ComputeNode(
+            hypervisor_type="a",
+            hypervisor_version=6.1,
+            free_ram_mb=513,
+            memory_mb=512,
+            ram_allocation_ratio=1.0,
+        )
         self.task._get_compute_info(self.destination)\
                 .AndReturn(hypervisor_details)
         self.task._get_compute_info(self.instance_host)\
@@ -194,9 +196,15 @@ def test_check_requested_destination_fails_with_not_enough_memory(self):
 
         self.task._check_host_is_up(self.destination)
         objects.ComputeNode.get_first_node_by_host_for_old_compat(self.context,
-            self.destination).AndReturn({"free_ram_mb": 511})
+            self.destination).AndReturn(
+                objects.ComputeNode(free_ram_mb=513,
+                                    memory_mb=1024,
+                                    ram_allocation_ratio=0.9,
+                                    ))
 
         self.mox.ReplayAll()
+        # free_ram is bigger than instance.ram (512) but the allocation ratio
+        # reduces the total available RAM to 410MB (1024 * 0.9 - (1024 - 513))
         self.assertRaises(exception.MigrationPreCheckError,
                           self.task._check_requested_destination)