Add nova file_backed_memory and memory_backing_dir support for qemu.conf

The libvirt driver now allows utilizing file backed memory for qemu/KVM
virtual machines, via a new configuration attribute
``[libvirt]/file_backed_memory``, defaulting to 0 (disabled).

``[libvirt]/file_backed_memory`` specifies the available capacity in MiB
for file backed memory, at the directory configured for
``memory_backing_dir`` in libvirt's ``qemu.conf``. When enabled, the
libvirt driver will report the configured value for the total memory
capacity of the node, and will report used memory as the sum of all
configured guest memory.

Running Nova with file_backed_memory requires libvirt version 4.0.0 and
qemu version 2.6.0

Related-Bug: 1793687

Change-Id: I0d9eb21fcab01266e501b7fc63c5b2bbb244956a

manifests/compute/libvirt.pp

@@ -147,6 +147,10 @@
 #   Valid values are 256, 512, 1024
 #   Defaults to $::os_service_default
 #
+# [*file_backed_memory*]
+#   (optional) Available capacity in MiB for file-backed memory.
+#   Defaults to $::os_service_default
+#
 class nova::compute::libvirt (
   $ensure_package                             = 'present',
   $libvirt_virt_type                          = 'kvm',
@@ -175,6 +179,7 @@ class nova::compute::libvirt (
   $log_outputs                                = undef,
   $rx_queue_size                              = $::os_service_default,
   $tx_queue_size                              = $::os_service_default,
+  $file_backed_memory                         = undef,
 ) inherits nova::params {
 
   include ::nova::deps
@@ -256,6 +261,7 @@ class nova::compute::libvirt (
     'libvirt/enabled_perf_events':   value => join(any2array($libvirt_enabled_perf_events), ',');
     'libvirt/rx_queue_size':         value => $rx_queue_size;
     'libvirt/tx_queue_size':         value => $tx_queue_size;
+    'libvirt/file_backed_memory':    value => $file_backed_memory;
   }
 
   # cpu_model param is only valid if cpu_mode=custom

manifests/compute/libvirt/qemu.pp

@@ -28,13 +28,19 @@
 #   (optional) Enables TLS client cert verification when vnc_tls is enabled.
 #   Defaults to true.
 #
+# [*memory_backing_dir*]
+#   (optional) This directory is used for memoryBacking source if configured as file.
+#   NOTE: big files will be stored here
+#   Defaults to undef.
+#
 class nova::compute::libvirt::qemu(
   $configure_qemu     = false,
   $group              = undef,
   $max_files          = 1024,
   $max_processes      = 4096,
   $vnc_tls            = false,
-  $vnc_tls_verify = true
+  $vnc_tls_verify     = true,
+  $memory_backing_dir = undef
 ){
 
   include ::nova::deps
@@ -68,7 +74,12 @@ class nova::compute::libvirt::qemu(
     } else {
       $augues_group_changes = []
     }
-    $augues_changes = concat($augues_changes_default, $augues_group_changes)
+    if $memory_backing_dir and !empty($memory_backing_dir) {
+      $augues_memory_backing_dir_changes = ["set memory_backing_dir ${memory_backing_dir}"]
+    } else {
+      $augues_memory_backing_dir_changes = []
+    }
+    $augues_changes = concat($augues_changes_default, $augues_group_changes, $augues_memory_backing_dir_changes)
 
     augeas { 'qemu-conf-limits':
       context => '/files/etc/libvirt/qemu.conf',
@@ -83,7 +94,8 @@ class nova::compute::libvirt::qemu(
         'rm max_processes',
         'rm group',
         'rm vnc_tls',
-        'rm vnc_tls_x509_verify'
+        'rm vnc_tls_x509_verify',
+        'rm memory_backing_dir'
       ],
       tag     => 'qemu-conf-augeas',
     }

releasenotes/notes/nova_file_backed_memory_and_memory_backing_dir_support_for_qemu-a4cde7ab5297f3ac.yaml

@@ -0,0 +1,18 @@
+---
+features:
+  - |
+    Add nova file_backed_memory and memory_backing_dir support for qemu.conf
+
+    The libvirt driver now allows utilizing file backed memory for qemu/KVM
+    virtual machines, via a new configuration attribute
+    ``[libvirt]/file_backed_memory``, defaulting to 0 (disabled).
+
+    ``[libvirt]/file_backed_memory`` specifies the available capacity in MiB
+    for file backed memory, at the directory configured for
+    ``memory_backing_dir`` in libvirt's ``qemu.conf``. When enabled, the
+    libvirt driver will report the configured value for the total memory
+    capacity of the node, and will report used memory as the sum of all
+    configured guest memory.
+
+    Running Nova with file_backed_memory requires libvirt version 4.0.0 and
+    qemu version 2.6.0

spec/classes/nova_compute_libvirt_qemu_spec.rb

@@ -18,7 +18,7 @@ describe 'nova::compute::libvirt::qemu' do
       end
       it { is_expected.to contain_augeas('qemu-conf-limits').with({
         :context => '/files/etc/libvirt/qemu.conf',
-        :changes => [ "rm max_files", "rm max_processes", "rm group", "rm vnc_tls", "rm vnc_tls_x509_verify" ],
+        :changes => [ "rm max_files", "rm max_processes", "rm group", "rm vnc_tls", "rm vnc_tls_x509_verify", "rm memory_backing_dir" ],
       }).that_notifies('Service[libvirt]') }
     end
 
@@ -57,6 +57,7 @@ describe 'nova::compute::libvirt::qemu' do
           :group => 'openvswitch',
           :max_files => 32768,
           :max_processes => 131072,
+          :memory_backing_dir => '/tmp'
         }
       end
       it { is_expected.to contain_augeas('qemu-conf-limits').with({
@@ -66,7 +67,8 @@ describe 'nova::compute::libvirt::qemu' do
             "set max_processes 131072",
             "set vnc_tls 0",
             "set vnc_tls_x509_verify 0",
-            "set group openvswitch"
+            "set group openvswitch",
+            "set memory_backing_dir /tmp"
         ],
         :tag     => 'qemu-conf-augeas',
       }).that_notifies('Service[libvirt]') }