objects: add method to verify requested hugepages

Introduces a new method can_fit_hugepages to numa cell object

Work-Item: Enhance libvirt driver to configure guests based on
           the flavour parameter for page sizes

Partial-Implement: blueprint virt-driver-large-pages
Change-Id: I600840a96b13c1de4f2f409069f452e18e1c1c52

nova/exception.py

@@ -1818,3 +1818,7 @@ class MemoryPageSizeInvalid(Invalid):
 
 class MemoryPageSizeForbidden(Invalid):
     msg_fmt = _("Page size %(pagesize)s forbidden against '%(against)s'")
+
+
+class MemoryPageSizeNotSupported(Invalid):
+    msg_fmt = _("Page size %(pagesize)s is not supported by the host.")

nova/objects/numa.py

@@ -14,6 +14,7 @@
 
 from oslo.serialization import jsonutils
 
+from nova import exception
 from nova.objects import base
 from nova.objects import fields
 from nova.virt import hardware
@@ -73,6 +74,21 @@ class NUMACell(base.NovaObject):
                    cpu_usage=cpu_usage, memory_usage=memory_usage,
                    mempages=[])
 
+    def can_fit_hugepages(self, pagesize, memory):
+        """Returns whether memory can fit into hugepages size
+
+        :param pagesize: a page size in KibB
+        :param memory: a memory size asked to fit in KiB
+
+        :returns: whether memory can fit in hugepages
+        :raises: MemoryPageSizeNotSupported if page size not supported
+        """
+        for pages in self.mempages:
+            if pages.size_kb == pagesize:
+                return (memory <= pages.free_kb and
+                        (memory % pages.size_kb) == 0)
+        raise exception.MemoryPageSizeNotSupported(pagesize=pagesize)
+
 
 class NUMAPagesTopology(base.NovaObject):
     # Version 1.0: Initial version

nova/tests/unit/objects/test_numa.py

@@ -11,6 +11,7 @@
 #    under the License.
 
 
+from nova import exception
 from nova import objects
 from nova.tests.unit.objects import test_objects
 
@@ -57,6 +58,24 @@ class _TestNUMA(object):
         self.assertEqual(512, pages_topology.free)
         self.assertEqual(1048576, pages_topology.free_kb)
 
+    def test_can_fit_hugepages(self):
+        cell = objects.NUMACell(
+            id=0, cpuset=set([1, 2]), memory=1024,
+            mempages=[
+                objects.NUMAPagesTopology(
+                    size_kb=4, total=1548736, used=0),
+                objects.NUMAPagesTopology(
+                    size_kb=2048, total=513, used=0)])  # 1,002G
+
+        pagesize = 2048
+
+        self.assertTrue(cell.can_fit_hugepages(pagesize, 2 ** 20))
+        self.assertFalse(cell.can_fit_hugepages(pagesize, 2 ** 21))
+        self.assertFalse(cell.can_fit_hugepages(pagesize, 2 ** 19 + 1))
+        self.assertRaises(
+            exception.MemoryPageSizeNotSupported,
+            cell.can_fit_hugepages, 12345, 2 ** 20)
+
 
 class TestNUMA(test_objects._LocalTest,
                _TestNUMA):