domain: Introduce ./hugepages/page/[@size, @unit, @nodeset]

<memoryBacking>
    <hugepages>
      <page size="1" unit="G" nodeset="0-3,5"/>
      <page size="2" unit="M" nodeset="4"/>
    </hugepages>
  </memoryBacking>

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>

docs/formatdomain.html.in

@@ -617,7 +617,9 @@
 <domain>
   ...
   <memoryBacking>
-    <hugepages/>
+    <hugepages>
+      <page size="1" unit="G" nodeset="0-3,5"/>
+      <page size="2" unit="M" nodeset="4"/>
     <nosharepages/>
     <locked/>
   </memoryBacking>
@@ -632,7 +634,19 @@
     <dl>
       <dt><code>hugepages</code></dt>
       <dd>This tells the hypervisor that the guest should have its memory
-        allocated using hugepages instead of the normal native page size.</dd>
+      allocated using hugepages instead of the normal native page size.
+      <span class='since'>Since 1.2.5</span> it's possible to set hugepages
+      more specifically per numa node. The <code>page</code> element is
+      introduced. It has one compulsory attribute <code>size</code> which
+      specifies which hugepages should be used (especially useful on systems
+      supporting hugepages of different sizes). The default unit for the
+      <code>size</code> attribute is kilobytes (multiplier of 1024). If you
+      want to use different unit, use optional <code>unit</code> attribute.
+      For systems with NUMA, the optional <code>nodeset</code> attribute may
+      come handy as it ties given guest's NUMA nodes to certain hugepage
+      sizes. From the example snippet, one gigabyte hugepages are used for
+      every NUMA node except node number four. For the correct syntax see
+      <a href="#elementsNUMATuning">this</a>.</dd>
       <dt><code>nosharepages</code></dt>
       <dd>Instructs hypervisor to disable shared pages (memory merge, KSM) for
         this domain. <span class="since">Since 1.0.6</span></dd>

docs/schemas/domaincommon.rng

@@ -568,7 +568,24 @@
           <interleave>
             <optional>
               <element name="hugepages">
-                <empty/>
+                <zeroOrMore>
+                  <element name="page">
+                    <attribute name="size">
+                      <ref name="unsignedLong"/>
+                    </attribute>
+                    <optional>
+                      <attribute name='unit'>
+                        <ref name='unit'/>
+                      </attribute>
+                    </optional>
+                    <optional>
+                      <attribute name="nodeset">
+                        <ref name='cpuset'/>
+                      </attribute>
+                    </optional>
+                    <empty/>
+                  </element>
+                </zeroOrMore>
               </element>
             </optional>
             <optional>