From 9b9a712ec4e96e2af2d05476cb7e48c8d1602f16 Mon Sep 17 00:00:00 2001
From: Liam Young <liam.young@canonical.com>
Date: Thu, 9 Feb 2017 11:57:45 +0000
Subject: [PATCH] Lower vm.swappiness to reduce guest memory latency

Lowering the value of vm.swappiness to 1 (minimum amount of
swapping without disabling it entirely) should reduce the
guest memory latency.

The default of 1 in the charm can be changed by the user by
explicitly setting vm.swappiness in the sysctl charm setting.

Change-Id: If9d3a9a0d15a84b86cfa7ba3620b66e7ea61d414
Closes-Bug: 1660248
---
 hooks/nova_compute_hooks.py           | 10 +++++++---
 unit_tests/test_nova_compute_hooks.py | 19 +++++++++++++++++--
 2 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/hooks/nova_compute_hooks.py b/hooks/nova_compute_hooks.py
index 9b917650..a5919ff5 100755
--- a/hooks/nova_compute_hooks.py
+++ b/hooks/nova_compute_hooks.py
@@ -17,6 +17,7 @@
 import platform
 import sys
 import uuid
+import yaml
 
 from charmhelpers.core.hookenv import (
     Hooks,
@@ -149,9 +150,12 @@ def config_changed():
             do_openstack_upgrade(CONFIGS)
             send_remote_restart = True
 
-    sysctl_dict = config('sysctl')
-    if sysctl_dict:
-        create_sysctl(sysctl_dict, '/etc/sysctl.d/50-nova-compute.conf')
+    sysctl_settings = config('sysctl')
+    if sysctl_settings:
+        sysctl_dict = yaml.safe_load(sysctl_settings)
+        sysctl_dict['vm.swappiness'] = sysctl_dict.get('vm.swappiness', 1)
+        create_sysctl(yaml.dump(sysctl_dict),
+                      '/etc/sysctl.d/50-nova-compute.conf')
 
     destroy_libvirt_network('default')
 
diff --git a/unit_tests/test_nova_compute_hooks.py b/unit_tests/test_nova_compute_hooks.py
index f48114a1..a879d0da 100644
--- a/unit_tests/test_nova_compute_hooks.py
+++ b/unit_tests/test_nova_compute_hooks.py
@@ -236,9 +236,24 @@ class NovaComputeRelationsTests(CharmTestCase):
     @patch.object(hooks, 'compute_joined')
     def test_config_changed_with_sysctl(self, compute_joined):
         self.git_install_requested.return_value = False
-        self.test_config.set('sysctl', '{ kernel.max_pid : "1337" }')
+        self.test_config.set(
+            'sysctl',
+            '{ kernel.max_pid : "1337", vm.swappiness : 10 }')
         hooks.config_changed()
-        self.assertTrue(self.create_sysctl.called)
+        self.create_sysctl.assert_called_with(
+            "{kernel.max_pid: '1337', vm.swappiness: 10}\n",
+            '/etc/sysctl.d/50-nova-compute.conf')
+
+    @patch.object(hooks, 'compute_joined')
+    def test_config_changed_with_sysctl_swappy_default(self, compute_joined):
+        self.git_install_requested.return_value = False
+        self.test_config.set(
+            'sysctl',
+            '{ kernel.max_pid : "1337" }')
+        hooks.config_changed()
+        self.create_sysctl.assert_called_with(
+            "{kernel.max_pid: '1337', vm.swappiness: 1}\n",
+            '/etc/sysctl.d/50-nova-compute.conf')
 
     @patch.object(hooks, 'config_value_changed')
     def test_config_changed_git(self, config_val_changed):