VIOMB(4)						   BSD Kernel Interfaces Manual 						  VIOMB(4)

NAME

     viomb -- VirtIO memory ballooning driver

SYNOPSIS

     virtio* at pci? dev ? function ?
     viomb*  at virtio?

DESCRIPTION

     virtio(4) defines an interface for efficient, standard, and extensible I/O between the hypervisor and the virtual machine.  The viomb driver
     supports the virtio-compliant memory ballooning device.

     Memory ballooning works as follows:

     1.   The host operator requests a guest to return some amount of memory to the host (via e.g. Qemu monitor balloon command).
     2.   The hypervisor sends the request via VirtIO memory ballooning device.
     3.   The guest viomb driver requests allocation of that amount of physical memory from the NetBSD memory management system.
     4.   The viomb device tells the hypervisor the guest physical memory address of the allocated memory via VirtIO memory ballooning device.

     The sysctl node hw.viomb.npages shows the requested number of memory pages to return to the hypervisor, while hw.viomb.actual shows the
     actual number of memory pages that are already returned to the hypervisor.

SEE ALSO

     virtio(4), sysctl(8)

     Rusty Russell, IBM Corporation, Virtio PCI Card Specification, http://ozlabs.org/~rusty/virtio-spec/.

HISTORY

     The viomb device driver appeared in NetBSD 6.0.

BUGS

     The userland interface should be same as the Xen ballooning device.

BSD
								 November 26, 2011							       BSD