I have the same question, although I am especially interested in Windows 2003 Server (32-bit & 64-bit) applications.

Also on the issue of virtio drivers, it is disappointing that the Fedora drivers are still at 1.1.11-0 while the Red Hat labs virtio drivers were already at 1.1.15 as of two months ago [September 16, Ref: https://bugzilla.redhat.com/show_bug.cgi?id=610787]

This and the lack of documentation is surprising for a technology that Red Hat states is one of its highest priorities!

actually, the driver versions are the same. I had a look at redhat latest (virtio-win-1.1.16) and it actually packs the exact same driver versions. The difference is, of course, that redhat's are signed by whcl, whereas the fedora's are not.

To get the balloon driver loaded have a look at the installation notes in balloon.inf. You can get the command line device manager utility (devcon.exe) needed from http://support.microsoft.com/kb/311272.

Reboot and install the balloon service with the blnsvr.exe tool...

I'm using VMM 0.8.5 and the balloon device is being added to the qemu-kvm command by libvirt without having to add any "hardware". Didn't find this out until the driver and service was installed so perhaps could have added via Device Manager, this device didn't trigger the 'new hardware' wizard, though there were a number of unknown devices that look to have been added before I got the guest driver loaded.

The memory ballooning driver for Windows 7/2008 may not work because Windows automatically recognizes it as a "PCI standard RAM Controller". You can look at the properties of this system device and under details make sure that "Location information" shows the same PCI device that kvm/qemu set for the memory ballooning driver (in my case, it is PCI bus 0, device 5, function 0).

Be sure to go back to the Driver tab and update your driver to the actual balloon driver for this device rather than trying to manually install it by hand.

I wanted to put this here because this paged led me to the solution.

After much trouble with WindowsXP SP3 I found reference to devcon and the necessary Device ID in the balloon.inf file. WindowsXP had picked up the device (PCI\VEN_1AF4&DEV_1002) as, "PCI standard RAM Controller".

The balloon.inf file however misleading text which resulted in several failures and the 'installation' of several 'matching' devices as I found with the following command: devcon find PCI\VEN_1AF4&DEV_1002

I have found that running the following command from the appropriate balloon driver subdirectory does work.

devcon install BALLOON.inf "PCI\VEN_1AF4&DEV_1002&SUBSYS_00051AF4&REV_00"

-i

While this information is available elsewhere it is pertinent here as well. Installation and uninstallation of the balloon driver service can be completed from the appropriate balloon driver subdirectory using the following commands respectively.

blnsvr -i
blnsvr -u

I recommend installing the blnsvr (BalloonService) after installing the driver according to my previous post. Uninstalling will not remove the driver installed via devcon. Installation of the blnsvr will not install the driver.

-i

Latest news was adding the win-driver. All documentation indicates win-guests still can't release unused ram.
Are there any news? KSM is fine, but I experienced no big ram savings.

ps.:
qemu-kvm-0.14.0
guest win2k8r2, driver and service installed

Sorry, actually KSM works great and I just miscalculated my savings =/
Nevermind, but is there a date for ballooning in win-guests?
Cheers Michael