[libvirt] [PATCH 1/2] conf: introduce 'deflate-on-oom' attribute for memballoon device

[Dmitry Andreev]

Excessive memory balloon inflation can cause invocation of OOM-killer,
when Linux is under severe memory pressure. QEMU memballoon device
has a feature to release some memory at the last moment before some
process will be get killed by OOM-killer.

Introduced attribute allows to enable or disable this feature.
---
 docs/formatdomain.html.in     | 10 ++++++++++
 docs/schemas/domaincommon.rng |  5 +++++
 src/conf/domain_conf.c        | 23 +++++++++++++++++++++++
 src/conf/domain_conf.h        |  1 +
 4 files changed, 39 insertions(+)

diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
index a8bd48e..fa68e7b 100644
--- a/docs/formatdomain.html.in
+++ b/docs/formatdomain.html.in
@@ -5954,6 +5954,16 @@ qemu-kvm -net nic,model=? /dev/null
           <li>'xen' — default with Xen</li>
         </ul>
       </dd>
+      <dt><code>deflate-on-oom</code></dt>
+      <dd>
+        <p>
+          The optional <code>deflate-on-oom</code> attribute allows to
+          enable/disable (values "on"/"off", respectively) the ability of the
+          QEMU virtio memory balloon to release some memory at the last moment
+          before a guest's process get killed by OOM-killer.
+          <span class="since">Since 1.3.1, QEMU and KVM only</span>
+        </p>
+      </dd>
       <dt><code>period</code></dt>
       <dd>
         <p>
diff --git a/docs/schemas/domaincommon.rng b/docs/schemas/domaincommon.rng
index 4804c69..9587849 100644
--- a/docs/schemas/domaincommon.rng
+++ b/docs/schemas/domaincommon.rng
@@ -3415,6 +3415,11 @@
           <value>none</value>
         </choice>
       </attribute>
+      <optional>
+        <attribute name="deflate-on-oom">
+          <ref name="virOnOff"/>
+        </attribute>
+      </optional>
       <interleave>
         <optional>
           <ref name="alias"/>
diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index 5200c27..b332097 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -11312,6 +11312,7 @@ virDomainMemballoonDefParseXML(xmlNodePtr node,
                                unsigned int flags)
 {
     char *model;
+    char *deflate;
     virDomainMemballoonDefPtr def;
     xmlNodePtr save = ctxt->node;
     unsigned int period = 0;
@@ -11332,6 +11333,13 @@ virDomainMemballoonDefParseXML(xmlNodePtr node,
         goto error;
     }
 
+    if ((deflate = virXMLPropString(node, "deflate-on-oom")) &&
+        (def->deflate = virTristateSwitchTypeFromString(deflate)) < 0) {
+        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                       _("invalid deflate-on-oom attribute value '%s'"), deflate);
+        goto error;
+    }
+
     ctxt->node = node;
     if (virXPathUInt("string(./stats/@period)", ctxt, &period) < -1) {
         virReportError(VIR_ERR_XML_ERROR, "%s",
@@ -11350,6 +11358,7 @@ virDomainMemballoonDefParseXML(xmlNodePtr node,
 
  cleanup:
     VIR_FREE(model);
+    VIR_FREE(deflate);
 
     ctxt->node = save;
     return def;
@@ -17223,6 +17232,15 @@ virDomainMemballoonDefCheckABIStability(virDomainMemballoonDefPtr src,
         return false;
     }
 
+    if (src->deflate != dst->deflate) {
+        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                       _("Target balloon deflate-on-oom attribute value "
+                         "%s does not match source %s"),
+                       virTristateSwitchTypeToString(dst->deflate),
+                       virTristateSwitchTypeToString(src->deflate));
+        return false;
+    }
+
     if (!virDomainDeviceInfoCheckABIStability(&src->info, &dst->info))
         return false;
 
@@ -20390,6 +20408,7 @@ virDomainMemballoonDefFormat(virBufferPtr buf,
                              unsigned int flags)
 {
     const char *model = virDomainMemballoonModelTypeToString(def->model);
+    const char *deflate = virTristateSwitchTypeToString(def->deflate);
     virBuffer childrenBuf = VIR_BUFFER_INITIALIZER;
     int indent = virBufferGetIndent(buf, false);
 
@@ -20400,6 +20419,10 @@ virDomainMemballoonDefFormat(virBufferPtr buf,
     }
 
     virBufferAsprintf(buf, "<memballoon model='%s'", model);
+
+    if (def->deflate > 0 && deflate)
+        virBufferAsprintf(buf, " deflate-on-oom='%s'", deflate);
+
     virBufferAdjustIndent(&childrenBuf, indent + 2);
 
     if (def->period)
diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
index cec681a..707ffb2 100644
--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@@ -1634,6 +1634,7 @@ struct _virDomainMemballoonDef {
     int model;
     virDomainDeviceInfo info;
     int period; /* seconds between collections */
+    int deflate; /* enum virTristateSwitch */
 };
 
 struct _virDomainNVRAMDef {
-- 
1.8.3.1