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