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Post-Copy Live Migration of Virtual Machines

Authors (if Research)
Michael Hines, Umesh Deshpande, and Kartik Gopalan
Operating Regions
Operating Countries
Binghamton University (SUNY) Abstract: We present the design, implementation, and evaluation of post-copy based live migration for virtual machines (VMs) across a Gigabit LAN. Post-copy migration defers the transfer of a VM's memory contents until after its processor state has been sent to the target host. This deferral is in contrast to the traditional pre-copy approach, which first copies the memory state over multiple iterations followed by a final transfer of the processor state. The post-copy strategy can provide a "win-win" by reducing total migration time while maintaining the liveness of the VM during migration. We compare post-copy extensively against the traditional pre-copy approach on the Xen Hypervisor. Using a range of VM workloads we show that post-copy improves several metrics including pages transferred, total migration time, and network overhead. We facilitate the use of post-copy with adaptive prepaging techniques to minimize the number of page faults across the network. We propose different prepaging strategies and quantitatively compare their effectiveness in reducing network-bound page faults. Finally, we eliminate the transfer of free memory pages in both pre-copy and post-copy through a dynamic self-ballooning (DSB) mechanism. DSB periodically reclaims free pages from a VM and significantly speeds up migration with negligible performance impact on VM workload.
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