[PATCH 1/1] Optional free-page-reporting can be enabled/disabled for memballon device of model 'virtio'.

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xml:
<devices>
  <memballoon model='virtio' free-page-reporting='on'/>
</devices>

qemu:
qemu -device virtio-balloon-pci,...,free-page-reporting=on

This kernel feature allows for more stable and resource friendly systems.

Signed-off-by: Nico Pache <npache@xxxxxxxxxx>
---
 docs/formatdomain.rst                         |  6 ++++++
 docs/schemas/domaincommon.rng                 |  5 +++++
 src/conf/domain_conf.c                        | 21 +++++++++++++++++++
 src/conf/domain_conf.h                        |  1 +
 src/qemu/qemu_capabilities.c                  |  4 +++-
 src/qemu/qemu_capabilities.h                  |  1 +
 src/qemu/qemu_command.c                       |  5 +++++
 src/qemu/qemu_validate.c                      |  7 +++++++
 .../caps_5.1.0.x86_64.xml                     |  1 +
 .../caps_5.2.0.x86_64.xml                     |  1 +
 10 files changed, 51 insertions(+), 1 deletion(-)

diff --git a/docs/formatdomain.rst b/docs/formatdomain.rst
index f3cf9e1fb3..f4c7765f5f 100644
--- a/docs/formatdomain.rst
+++ b/docs/formatdomain.rst
@@ -6755,6 +6755,12 @@ Example: manually added device with static PCI slot 2 requested
    release some memory at the last moment before a guest's process get killed by
    Out of Memory killer. :since:`Since 1.3.1, QEMU and KVM only`
 
+``free-page-reporting``
+   The optional ``free-page-reporting`` attribute allows to enable/disable
+   ("on"/"off", respectively) the ability of the QEMU virtio memory balloon to
+   return unused pages back to the hypervisor to be used by other guests or
+   processes. :since:`Since 5.1, QEMU and KVM only`
+
 ``period``
    The optional ``period`` allows the QEMU virtio memory balloon driver to
    provide statistics through the ``virsh dommemstat           [domain]``
diff --git a/docs/schemas/domaincommon.rng b/docs/schemas/domaincommon.rng
index 4b7e460148..4c32b3555f 100644
--- a/docs/schemas/domaincommon.rng
+++ b/docs/schemas/domaincommon.rng
@@ -4539,6 +4539,11 @@
           <ref name="virOnOff"/>
         </attribute>
       </optional>
+      <optional>
+         <attribute name="free-page-reporting">
+           <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 b80d7c7c6c..f4b8e8d8c3 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -15384,6 +15384,7 @@ virDomainMemballoonDefParseXML(virDomainXMLOptionPtr xmlopt,
     VIR_XPATH_NODE_AUTORESTORE(ctxt)
     unsigned int period = 0;
     g_autofree char *model = NULL;
+    g_autofree char *freepage_reporting = NULL;
     g_autofree char *deflate = NULL;
 
     if (VIR_ALLOC(def) < 0)
@@ -15409,6 +15410,13 @@ virDomainMemballoonDefParseXML(virDomainXMLOptionPtr xmlopt,
         goto error;
     }
 
+   if ((freepage_reporting = virXMLPropString(node, "free-page-reporting")) &&
+       (def->free_page_reporting = virTristateSwitchTypeFromString(freepage_reporting)) <= 0) {
+       virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                       _("invalid free-page-reporting attribute value '%s'"), freepage_reporting);
+         goto error;
+     }
+
     ctxt->node = node;
     if (virXPathUInt("string(./stats/@period)", ctxt, &period) < -1) {
         virReportError(VIR_ERR_XML_ERROR, "%s",
@@ -23630,6 +23638,15 @@ virDomainMemballoonDefCheckABIStability(virDomainMemballoonDefPtr src,
         return false;
     }
 
+    if (src->free_page_reporting != dst->free_page_reporting) {
+        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                       _("Target balloon free-page-reporting attribute value "
+                         "'%s' does not match source '%s'"),
+                       virTristateSwitchTypeToString(dst->free_page_reporting),
+                       virTristateSwitchTypeToString(src->free_page_reporting));
+        return false;
+     }
+
     if (src->virtio && dst->virtio &&
         !virDomainVirtioOptionsCheckABIStability(src->virtio, dst->virtio))
         return false;
@@ -27737,6 +27754,10 @@ virDomainMemballoonDefFormat(virBufferPtr buf,
         virBufferAsprintf(&attrBuf, " autodeflate='%s'",
                           virTristateSwitchTypeToString(def->autodeflate));
 
+    if (def->free_page_reporting != VIR_TRISTATE_SWITCH_ABSENT)
+         virBufferAsprintf(&attrBuf, " free-page-reporting='%s'",
+                  virTristateSwitchTypeToString(def->free_page_reporting));
+
     if (def->period)
         virBufferAsprintf(&childrenBuf, "<stats period='%i'/>\n", def->period);
 
diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
index 9a44315519..f5f8baf32c 100644
--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@@ -1790,6 +1790,7 @@ struct _virDomainMemballoonDef {
     virDomainDeviceInfo info;
     int period; /* seconds between collections */
     int autodeflate; /* enum virTristateSwitch */
+    int free_page_reporting; /* enum virTristateSwitch */
     virDomainVirtioOptionsPtr virtio;
 };
 
diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
index 5dcfcd574d..88a2c8aacb 100644
--- a/src/qemu/qemu_capabilities.c
+++ b/src/qemu/qemu_capabilities.c
@@ -600,7 +600,8 @@ VIR_ENUM_IMPL(virQEMUCaps,
 
               /* 380 */
               "usb-host.hostdevice",
-    );
+              "virtio-balloon-pci.free-page-reporting",
+        );
 
 
 typedef struct _virQEMUCapsMachineType virQEMUCapsMachineType;
@@ -1344,6 +1345,7 @@ static struct virQEMUCapsDevicePropsFlags virQEMUCapsDevicePropsVirtioBalloon[]
     { "iommu_platform", QEMU_CAPS_VIRTIO_PCI_IOMMU_PLATFORM, NULL },
     { "ats", QEMU_CAPS_VIRTIO_PCI_ATS, NULL },
     { "packed", QEMU_CAPS_VIRTIO_PACKED_QUEUES, NULL },
+    { "free-page-reporting", QEMU_CAPS_VIRTIO_BALLOON_FREE_PAGE_REPORTING, NULL },
 };
 
 
diff --git a/src/qemu/qemu_capabilities.h b/src/qemu/qemu_capabilities.h
index 98d70cfa0e..6f39bf156f 100644
--- a/src/qemu/qemu_capabilities.h
+++ b/src/qemu/qemu_capabilities.h
@@ -580,6 +580,7 @@ typedef enum { /* virQEMUCapsFlags grouping marker for syntax-check */
 
     /* 380 */
     QEMU_CAPS_USB_HOST_HOSTDEVICE, /* -device usb-host.hostdevice */
+    QEMU_CAPS_VIRTIO_BALLOON_FREE_PAGE_REPORTING, /*virtio balloon free-page-reporting */
 
     QEMU_CAPS_LAST /* this must always be the last item */
 } virQEMUCapsFlags;
diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index e9ba81d82f..f80efaf026 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -3830,6 +3830,11 @@ qemuBuildMemballoonCommandLine(virCommandPtr cmd,
                           virTristateSwitchTypeToString(def->memballoon->autodeflate));
     }
 
+    if (def->memballoon->free_page_reporting != VIR_TRISTATE_SWITCH_ABSENT) {
+       virBufferAsprintf(&buf, ",free-page-reporting=%s",
+                  virTristateSwitchTypeToString(def->memballoon->free_page_reporting));
+    }
+
     qemuBuildVirtioOptionsStr(&buf, def->memballoon->virtio);
 
     if (qemuCommandAddExtDevice(cmd, &def->memballoon->info) < 0)
diff --git a/src/qemu/qemu_validate.c b/src/qemu/qemu_validate.c
index a212605579..cfeb1e67c4 100644
--- a/src/qemu/qemu_validate.c
+++ b/src/qemu/qemu_validate.c
@@ -3926,6 +3926,13 @@ qemuValidateDomainDeviceDefMemballoon(const virDomainMemballoonDef *memballoon,
         return -1;
     }
 
+    if (memballoon->free_page_reporting != VIR_TRISTATE_SWITCH_ABSENT &&
+         !virQEMUCapsGet(qemuCaps, QEMU_CAPS_VIRTIO_BALLOON_FREE_PAGE_REPORTING)) {
+         virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                        _("free-page-reporting is not supported by this QEMU binary"));
+         return -1;
+     }
+
     if (qemuValidateDomainVirtioOptions(memballoon->virtio, qemuCaps) < 0)
         return -1;
 
diff --git a/tests/qemucapabilitiesdata/caps_5.1.0.x86_64.xml b/tests/qemucapabilitiesdata/caps_5.1.0.x86_64.xml
index 987beb965e..1f1615b94b 100644
--- a/tests/qemucapabilitiesdata/caps_5.1.0.x86_64.xml
+++ b/tests/qemucapabilitiesdata/caps_5.1.0.x86_64.xml
@@ -243,6 +243,7 @@
   <flag name='numa.hmat'/>
   <flag name='blockdev-hostdev-scsi'/>
   <flag name='usb-host.hostdevice'/>
+  <flag name='virtio-balloon-pci.free-page-reporting'/>
   <version>5001000</version>
   <kvmVersion>0</kvmVersion>
   <microcodeVersion>43100242</microcodeVersion>
diff --git a/tests/qemucapabilitiesdata/caps_5.2.0.x86_64.xml b/tests/qemucapabilitiesdata/caps_5.2.0.x86_64.xml
index 3ee678ef8f..82f9051101 100644
--- a/tests/qemucapabilitiesdata/caps_5.2.0.x86_64.xml
+++ b/tests/qemucapabilitiesdata/caps_5.2.0.x86_64.xml
@@ -243,6 +243,7 @@
   <flag name='numa.hmat'/>
   <flag name='blockdev-hostdev-scsi'/>
   <flag name='usb-host.hostdevice'/>
+  <flag name='virtio-balloon-pci.free-page-reporting'/>
   <version>5001050</version>
   <kvmVersion>0</kvmVersion>
   <microcodeVersion>43100243</microcodeVersion>
-- 
2.18.4




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