Stop swap allocations being wrong due to MB vs GB

Swap is in MB, but allocations for disk are in GB.

We totally should claim disk in GB, for now lets just round up the swap
allocation to the next GB. While this is wasteful, its the only safe
answer to ensure you don't over commit resources on the node.

Updated the test so the swap is 1023MB, after rounding up this should
claim the same 1GB extra space for swap.

Closes-Bug: #1659266

Change-Id: If50eab870b2c50f4055668143780574e1350a438

nova/scheduler/client/report.py

@@ -87,6 +87,15 @@ def safe_connect(f):
     return wrapper
 
 
+def _convert_mb_to_ceil_gb(mb_value):
+    gb_int = 0
+    if mb_value:
+        gb_float = mb_value / 1024.0
+        # ensure we reserve/allocate enough space by rounding up to nearest GB
+        gb_int = int(math.ceil(gb_float))
+    return gb_int
+
+
 def _compute_node_to_inventory_dict(compute_node):
     """Given a supplied `objects.ComputeNode` object, return a dict, keyed
     by resource class, of various inventory information.
@@ -116,13 +125,9 @@ def _compute_node_to_inventory_dict(compute_node):
             'allocation_ratio': compute_node.ram_allocation_ratio,
         }
     if compute_node.local_gb > 0:
-        reserved_disk_gb = 0
         # TODO(johngarbutt) We should either move to reserved_host_disk_gb
         # or start tracking DISK_MB.
-        if CONF.reserved_host_disk_mb:
-            reserved_disk_gb = CONF.reserved_host_disk_mb / 1024.0
-            # ensure we reserve enough space by rounding up to nearest GB
-            reserved_disk_gb = int(math.ceil(reserved_disk_gb))
+        reserved_disk_gb = _convert_mb_to_ceil_gb(CONF.reserved_host_disk_mb)
         result[DISK_GB] = {
             'total': compute_node.local_gb,
             'reserved': reserved_disk_gb,
@@ -143,9 +148,11 @@ def _instance_to_allocations_dict(instance):
     # NOTE(danms): Boot-from-volume instances consume no local disk
     is_bfv = compute_utils.is_volume_backed_instance(instance._context,
                                                      instance)
+    # TODO(johngarbutt) we have to round up swap MB to the next GB.
+    # It would be better to claim disk in MB, but that is hard now.
+    swap_in_gb = _convert_mb_to_ceil_gb(instance.flavor.swap)
     disk = ((0 if is_bfv else instance.flavor.root_gb) +
-            instance.flavor.swap +
-            instance.flavor.ephemeral_gb)
+            swap_in_gb + instance.flavor.ephemeral_gb)
     alloc_dict = {
         MEMORY_MB: instance.flavor.memory_mb,
         VCPU: instance.flavor.vcpus,

nova/tests/unit/scheduler/client/test_report.py

@@ -1106,7 +1106,7 @@ class TestAllocations(SchedulerReportClientTestCase):
         inst = objects.Instance(
             uuid=uuids.inst,
             flavor=objects.Flavor(root_gb=10,
-                                  swap=1,
+                                  swap=1023,
                                   ephemeral_gb=100,
                                   memory_mb=1024,
                                   vcpus=2))