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VIOMB(4) BSD Kernel Interfaces Manual VIOMB(4)
viomb -- VirtIO memory ballooning driver
virtio* at pci? dev ? function ?
viomb* at virtio?
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
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 allo-
cated 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.
Rusty Russell, IBM Corporation, Virtio PCI Card Specification,
The viomb device driver appeared in NetBSD 6.0.
The userland interface should be same as the Xen ballooning device.
BSD November 26, 2011 BSD
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