Improving Live Migration Efficiency in QEMU: A Paravirtualized Approach

Virtual Machines are the key technology in cloud computing. In order to upgrade, repair or service the physical machine where a Virtual Machine is hosted, a common practice is to live-migrate the Virtual Machine to a different server. This involves copying all the guest memory over the network, which may take a non-negligible amount of time. In this work, we propose a technique to speed up the migration time by reducing the amount of guest memory to be transferred with the help of the guest OS. In particular, during live-migration, a paravirtualized driver running in the guest kernel obtains, and sends to the Virtual Machine Monitor, the list of guest page frames that are currently unused. The VMM can then safely skip these pages during the copy. We have integrated this technique in the live-migration implementation of QEMU [3], and we show the effects of our work in some experiments comparing the results against QEMU default implementation and VirtIO-Balloon.