From eda3c224589f87fae84cb059dc2571733ebd7ab4 Mon Sep 17 00:00:00 2001
From: Andrea Bolognani <abologna@redhat.com>
Date: Thu, 13 Jun 2019 12:55:10 +0200
Subject: [PATCH] guest: Add memory balloon by default

libvirt already does this for pretty much all QEMU guests, but
ARM virt guests for example don't get a memory balloon by default
at that level of the stack.

virt-manager is in a good position to make sure defaults are
consistent across architectures, and there's no downside in having
the device in the XML passed to libvirt anyway.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
---
 .../compare/virt-install-aarch64-graphics.xml |  1 +
 .../compare/virt-install-aarch64-headless.xml |  1 +
 .../compare/virt-install-aarch64-kvm-gic.xml  |  1 +
 .../virt-install-aarch64-kvm-import.xml       |  1 +
 .../virt-install-arm-defaultmach-f20.xml      |  1 +
 .../compare/virt-install-arm-kvm-import.xml   |  1 +
 .../compare/virt-install-arm-virt-f20.xml     |  1 +
 .../compare/virt-install-f21-kvm-remote.xml   |  1 +
 .../compare/virt-install-kvm-centos7.xml      |  2 ++
 .../virt-install-kvm-fedoralatest-url.xml     |  2 ++
 .../virt-install-kvm-session-defaults.xml     |  2 ++
 .../compare/virt-install-location-iso.xml     |  2 ++
 .../compare/virt-install-many-devices.xml     |  1 +
 ...virt-install-network-install-resources.xml |  2 ++
 ...virt-install-osinfo-netinst-unattended.xml |  2 ++
 .../virt-install-osinfo-url-unattended.xml    |  2 ++
 .../virt-install-osinfo-url-with-disk.xml     |  2 ++
 .../compare/virt-install-osinfo-url.xml       |  2 ++
 .../compare/virt-install-ppc64-graphics.xml   |  1 +
 .../compare/virt-install-ppc64-headless.xml   |  1 +
 .../virt-install-ppc64-machdefault-f20.xml    |  1 +
 .../virt-install-ppc64-pseries-f20.xml        |  1 +
 .../virt-install-ppc64le-kvm-import.xml       |  1 +
 .../compare/virt-install-qemu-32-on-64.xml    |  1 +
 .../compare/virt-install-riscv64-graphics.xml |  1 +
 .../compare/virt-install-riscv64-headless.xml |  1 +
 .../virt-install-s390x-cdrom-KVMIBM.xml       |  1 +
 .../compare/virt-install-s390x-cdrom.xml      |  1 +
 .../compare/virt-install-s390x-graphics.xml   |  1 +
 .../compare/virt-install-s390x-headless.xml   |  1 +
 .../compare/virt-install-x86_64-graphics.xml  |  1 +
 .../compare/virt-install-x86_64-headless.xml  |  1 +
 virtinst/guest.py                             | 32 +++++++++++++++++++
 33 files changed, 73 insertions(+)

diff --git a/tests/cli-test-xml/compare/virt-install-aarch64-graphics.xml b/tests/cli-test-xml/compare/virt-install-aarch64-graphics.xml
index d6972aff3..dad2636b8 100644
--- a/tests/cli-test-xml/compare/virt-install-aarch64-graphics.xml
+++ b/tests/cli-test-xml/compare/virt-install-aarch64-graphics.xml
@@ -40,6 +40,7 @@
     <video>
       <model type="virtio"/>
     </video>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-aarch64-headless.xml b/tests/cli-test-xml/compare/virt-install-aarch64-headless.xml
index 6bf62e3f1..86175a114 100644
--- a/tests/cli-test-xml/compare/virt-install-aarch64-headless.xml
+++ b/tests/cli-test-xml/compare/virt-install-aarch64-headless.xml
@@ -34,6 +34,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-aarch64-kvm-gic.xml b/tests/cli-test-xml/compare/virt-install-aarch64-kvm-gic.xml
index c979eb6f0..7346ad32a 100644
--- a/tests/cli-test-xml/compare/virt-install-aarch64-kvm-gic.xml
+++ b/tests/cli-test-xml/compare/virt-install-aarch64-kvm-gic.xml
@@ -41,6 +41,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-aarch64-kvm-import.xml b/tests/cli-test-xml/compare/virt-install-aarch64-kvm-import.xml
index 2ec1e7c59..a6eb94216 100644
--- a/tests/cli-test-xml/compare/virt-install-aarch64-kvm-import.xml
+++ b/tests/cli-test-xml/compare/virt-install-aarch64-kvm-import.xml
@@ -34,6 +34,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-arm-defaultmach-f20.xml b/tests/cli-test-xml/compare/virt-install-arm-defaultmach-f20.xml
index 6281d823c..7ddc645db 100644
--- a/tests/cli-test-xml/compare/virt-install-arm-defaultmach-f20.xml
+++ b/tests/cli-test-xml/compare/virt-install-arm-defaultmach-f20.xml
@@ -34,6 +34,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-arm-kvm-import.xml b/tests/cli-test-xml/compare/virt-install-arm-kvm-import.xml
index acd49a5da..1d11fd967 100644
--- a/tests/cli-test-xml/compare/virt-install-arm-kvm-import.xml
+++ b/tests/cli-test-xml/compare/virt-install-arm-kvm-import.xml
@@ -34,6 +34,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-arm-virt-f20.xml b/tests/cli-test-xml/compare/virt-install-arm-virt-f20.xml
index 056668763..4f52d8e84 100644
--- a/tests/cli-test-xml/compare/virt-install-arm-virt-f20.xml
+++ b/tests/cli-test-xml/compare/virt-install-arm-virt-f20.xml
@@ -34,6 +34,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-f21-kvm-remote.xml b/tests/cli-test-xml/compare/virt-install-f21-kvm-remote.xml
index 31b5fa667..0c79782db 100644
--- a/tests/cli-test-xml/compare/virt-install-f21-kvm-remote.xml
+++ b/tests/cli-test-xml/compare/virt-install-f21-kvm-remote.xml
@@ -57,6 +57,7 @@
     </video>
     <redirdev bus="usb" type="spicevmc"/>
     <redirdev bus="usb" type="spicevmc"/>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-kvm-centos7.xml b/tests/cli-test-xml/compare/virt-install-kvm-centos7.xml
index 6baaf1695..b17f819da 100644
--- a/tests/cli-test-xml/compare/virt-install-kvm-centos7.xml
+++ b/tests/cli-test-xml/compare/virt-install-kvm-centos7.xml
@@ -61,6 +61,7 @@
     </video>
     <redirdev bus="usb" type="spicevmc"/>
     <redirdev bus="usb" type="spicevmc"/>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
@@ -127,6 +128,7 @@
     </video>
     <redirdev bus="usb" type="spicevmc"/>
     <redirdev bus="usb" type="spicevmc"/>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-kvm-fedoralatest-url.xml b/tests/cli-test-xml/compare/virt-install-kvm-fedoralatest-url.xml
index 13030ebf9..c670ab7d7 100644
--- a/tests/cli-test-xml/compare/virt-install-kvm-fedoralatest-url.xml
+++ b/tests/cli-test-xml/compare/virt-install-kvm-fedoralatest-url.xml
@@ -51,6 +51,7 @@
     <video>
       <model type="qxl"/>
     </video>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
@@ -107,6 +108,7 @@
     <video>
       <model type="qxl"/>
     </video>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-kvm-session-defaults.xml b/tests/cli-test-xml/compare/virt-install-kvm-session-defaults.xml
index 17653d8bb..d5c3ce69e 100644
--- a/tests/cli-test-xml/compare/virt-install-kvm-session-defaults.xml
+++ b/tests/cli-test-xml/compare/virt-install-kvm-session-defaults.xml
@@ -66,6 +66,7 @@
     </video>
     <redirdev bus="usb" type="spicevmc"/>
     <redirdev bus="usb" type="spicevmc"/>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
@@ -135,6 +136,7 @@
     </video>
     <redirdev bus="usb" type="spicevmc"/>
     <redirdev bus="usb" type="spicevmc"/>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-location-iso.xml b/tests/cli-test-xml/compare/virt-install-location-iso.xml
index 94e171fca..24301520a 100644
--- a/tests/cli-test-xml/compare/virt-install-location-iso.xml
+++ b/tests/cli-test-xml/compare/virt-install-location-iso.xml
@@ -71,6 +71,7 @@
     </video>
     <redirdev bus="usb" type="spicevmc"/>
     <redirdev bus="usb" type="spicevmc"/>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
@@ -145,6 +146,7 @@
     </video>
     <redirdev bus="usb" type="spicevmc"/>
     <redirdev bus="usb" type="spicevmc"/>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-many-devices.xml b/tests/cli-test-xml/compare/virt-install-many-devices.xml
index 99e45e020..2369824c9 100644
--- a/tests/cli-test-xml/compare/virt-install-many-devices.xml
+++ b/tests/cli-test-xml/compare/virt-install-many-devices.xml
@@ -515,6 +515,7 @@
       <source path="/tmp/foo.socket"/>
       <log file="/tmp/123.log"/>
     </redirdev>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-network-install-resources.xml b/tests/cli-test-xml/compare/virt-install-network-install-resources.xml
index f43118f32..c77c8e3a6 100644
--- a/tests/cli-test-xml/compare/virt-install-network-install-resources.xml
+++ b/tests/cli-test-xml/compare/virt-install-network-install-resources.xml
@@ -43,6 +43,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
@@ -90,6 +91,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-osinfo-netinst-unattended.xml b/tests/cli-test-xml/compare/virt-install-osinfo-netinst-unattended.xml
index c36efa676..829054c88 100644
--- a/tests/cli-test-xml/compare/virt-install-osinfo-netinst-unattended.xml
+++ b/tests/cli-test-xml/compare/virt-install-osinfo-netinst-unattended.xml
@@ -49,6 +49,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
@@ -100,6 +101,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-osinfo-url-unattended.xml b/tests/cli-test-xml/compare/virt-install-osinfo-url-unattended.xml
index 8691c82ea..4a6311f73 100644
--- a/tests/cli-test-xml/compare/virt-install-osinfo-url-unattended.xml
+++ b/tests/cli-test-xml/compare/virt-install-osinfo-url-unattended.xml
@@ -43,6 +43,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
@@ -90,6 +91,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-osinfo-url-with-disk.xml b/tests/cli-test-xml/compare/virt-install-osinfo-url-with-disk.xml
index 96371ec99..b32b88da4 100644
--- a/tests/cli-test-xml/compare/virt-install-osinfo-url-with-disk.xml
+++ b/tests/cli-test-xml/compare/virt-install-osinfo-url-with-disk.xml
@@ -53,6 +53,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
@@ -110,6 +111,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-osinfo-url.xml b/tests/cli-test-xml/compare/virt-install-osinfo-url.xml
index 3d87a29e6..962c4bddf 100644
--- a/tests/cli-test-xml/compare/virt-install-osinfo-url.xml
+++ b/tests/cli-test-xml/compare/virt-install-osinfo-url.xml
@@ -43,6 +43,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
@@ -90,6 +91,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-ppc64-graphics.xml b/tests/cli-test-xml/compare/virt-install-ppc64-graphics.xml
index f5ed6f883..f65d95bc3 100644
--- a/tests/cli-test-xml/compare/virt-install-ppc64-graphics.xml
+++ b/tests/cli-test-xml/compare/virt-install-ppc64-graphics.xml
@@ -38,6 +38,7 @@
     <video>
       <model type="vga"/>
     </video>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-ppc64-headless.xml b/tests/cli-test-xml/compare/virt-install-ppc64-headless.xml
index a1f56b260..37aa13d5c 100644
--- a/tests/cli-test-xml/compare/virt-install-ppc64-headless.xml
+++ b/tests/cli-test-xml/compare/virt-install-ppc64-headless.xml
@@ -32,6 +32,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-ppc64-machdefault-f20.xml b/tests/cli-test-xml/compare/virt-install-ppc64-machdefault-f20.xml
index 199a21761..80810ba35 100644
--- a/tests/cli-test-xml/compare/virt-install-ppc64-machdefault-f20.xml
+++ b/tests/cli-test-xml/compare/virt-install-ppc64-machdefault-f20.xml
@@ -39,6 +39,7 @@
     <video>
       <model type="vga"/>
     </video>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-ppc64-pseries-f20.xml b/tests/cli-test-xml/compare/virt-install-ppc64-pseries-f20.xml
index 2e90c998a..787042dd3 100644
--- a/tests/cli-test-xml/compare/virt-install-ppc64-pseries-f20.xml
+++ b/tests/cli-test-xml/compare/virt-install-ppc64-pseries-f20.xml
@@ -44,6 +44,7 @@
     <video>
       <model type="vga"/>
     </video>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-ppc64le-kvm-import.xml b/tests/cli-test-xml/compare/virt-install-ppc64le-kvm-import.xml
index 4f6ad26c0..262178beb 100644
--- a/tests/cli-test-xml/compare/virt-install-ppc64le-kvm-import.xml
+++ b/tests/cli-test-xml/compare/virt-install-ppc64le-kvm-import.xml
@@ -38,6 +38,7 @@
     <video>
       <model type="vga"/>
     </video>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-qemu-32-on-64.xml b/tests/cli-test-xml/compare/virt-install-qemu-32-on-64.xml
index 47336f728..944a5f113 100644
--- a/tests/cli-test-xml/compare/virt-install-qemu-32-on-64.xml
+++ b/tests/cli-test-xml/compare/virt-install-qemu-32-on-64.xml
@@ -40,6 +40,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-riscv64-graphics.xml b/tests/cli-test-xml/compare/virt-install-riscv64-graphics.xml
index 61d2e7e63..eff7a2744 100644
--- a/tests/cli-test-xml/compare/virt-install-riscv64-graphics.xml
+++ b/tests/cli-test-xml/compare/virt-install-riscv64-graphics.xml
@@ -38,6 +38,7 @@
     <video>
       <model type="virtio"/>
     </video>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-riscv64-headless.xml b/tests/cli-test-xml/compare/virt-install-riscv64-headless.xml
index cc2b0ed8c..a0bb7c1be 100644
--- a/tests/cli-test-xml/compare/virt-install-riscv64-headless.xml
+++ b/tests/cli-test-xml/compare/virt-install-riscv64-headless.xml
@@ -32,6 +32,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-s390x-cdrom-KVMIBM.xml b/tests/cli-test-xml/compare/virt-install-s390x-cdrom-KVMIBM.xml
index 8af2aee83..803fc755d 100644
--- a/tests/cli-test-xml/compare/virt-install-s390x-cdrom-KVMIBM.xml
+++ b/tests/cli-test-xml/compare/virt-install-s390x-cdrom-KVMIBM.xml
@@ -46,6 +46,7 @@
       <model type="virtio"/>
     </video>
     <watchdog model="diag288" action="reset"/>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-s390x-cdrom.xml b/tests/cli-test-xml/compare/virt-install-s390x-cdrom.xml
index 33ca61906..c44245659 100644
--- a/tests/cli-test-xml/compare/virt-install-s390x-cdrom.xml
+++ b/tests/cli-test-xml/compare/virt-install-s390x-cdrom.xml
@@ -41,6 +41,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-s390x-graphics.xml b/tests/cli-test-xml/compare/virt-install-s390x-graphics.xml
index 2747254e8..f96abb002 100644
--- a/tests/cli-test-xml/compare/virt-install-s390x-graphics.xml
+++ b/tests/cli-test-xml/compare/virt-install-s390x-graphics.xml
@@ -39,6 +39,7 @@
     <video>
       <model type="virtio"/>
     </video>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-s390x-headless.xml b/tests/cli-test-xml/compare/virt-install-s390x-headless.xml
index c5344a5c8..863b69a0c 100644
--- a/tests/cli-test-xml/compare/virt-install-s390x-headless.xml
+++ b/tests/cli-test-xml/compare/virt-install-s390x-headless.xml
@@ -33,6 +33,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-x86_64-graphics.xml b/tests/cli-test-xml/compare/virt-install-x86_64-graphics.xml
index d03904016..85349b836 100644
--- a/tests/cli-test-xml/compare/virt-install-x86_64-graphics.xml
+++ b/tests/cli-test-xml/compare/virt-install-x86_64-graphics.xml
@@ -50,6 +50,7 @@
     <video>
       <model type="qxl"/>
     </video>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/tests/cli-test-xml/compare/virt-install-x86_64-headless.xml b/tests/cli-test-xml/compare/virt-install-x86_64-headless.xml
index 0a2d14a25..5014e3ca4 100644
--- a/tests/cli-test-xml/compare/virt-install-x86_64-headless.xml
+++ b/tests/cli-test-xml/compare/virt-install-x86_64-headless.xml
@@ -45,6 +45,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
diff --git a/virtinst/guest.py b/virtinst/guest.py
index 593d1cb3f..ef227d173 100644
--- a/virtinst/guest.py
+++ b/virtinst/guest.py
@@ -735,6 +735,7 @@ class Guest(XMLBuilder):
         self._add_default_usb_controller()
         self._add_default_channels()
         self._add_default_rng()
+        self._add_default_memballoon()
 
         self.clock.set_defaults(self)
         self.cpu.set_defaults(self)
@@ -946,6 +947,37 @@ class Guest(XMLBuilder):
             dev.device = "/dev/urandom"
             self.add_device(dev)
 
+    def _add_default_memballoon(self):
+        if self.devices.memballoon:
+            return
+        if not self.conn.is_qemu():
+            return
+
+        # For most QEMU guests, libvirt will automatically add a memballoon
+        # device, which means that if the user has explicitly asked for it
+        # *not* to be present then we still need to create the device and
+        # set the model to "none" to let libvirt know
+        if self.disable_default_memballoon:
+            dev = DeviceMemballoon(self.conn)
+            dev.model = "none"
+            self.add_device(dev)
+            return
+
+        # We know for certain that a memballoon is good to have with these
+        # machine types; for other machine types, we leave the decision up
+        # to libvirt
+        if not (self.os.is_x86() or
+                self.os.is_arm_machvirt() or
+                self.os.is_riscv_virt() or
+                self.os.is_s390x() or
+                self.os.is_pseries()):
+            return
+
+        if self.osinfo.supports_virtioballoon():
+            dev = DeviceMemballoon(self.conn)
+            dev.model = "virtio"
+            self.add_device(dev)
+
     def _add_implied_controllers(self):
         has_any_scsi = False
         for dev in self.devices.controller: