Updated: 2021/Apr/14

VIOMB(4)                     Device Drivers 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 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
     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.

     virtio(4), sysctl(8), x86/balloon(4)

     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.

NetBSD 9.99                     August 25, 2020                    NetBSD 9.99