VIOMB(4)                NetBSD 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 physi-
          cal 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.

NetBSD 6.0                     November 26, 2011                    NetBSD 6.0

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