Toward Virtual Machine Image Management for Persistent Memory

Abstract

Persistent memory’s (PM) byte-addressability and high capacity will also make it emerging for virtualized environment. Modern virtual machine monitors virtualize PM using either I/O virtualization or memory virtualization. However, I/O virtualization will sacrifice PM’s byte-addressability, and memory virtualization does not get the chance of PM image management. In this article, we enhance QEMU’s memory virtualization mechanism. The enhanced system can achieve both PM’s byte-addressability inside virtual machines and PM image management outside the virtual machines. We also design pcow , a virtual machine image format for PM, which is compatible with our enhanced memory virtualization and supports storage virtualization features including thin-provisioning, base image, snapshot, and striping. Address translation is performed with the help of the Extended Page Table, thus much faster than image formats implemented in I/O virtualization. We also optimize pcow considering PM’s characteristics. We perform exhaustive performance evaluations on an x86 server equipping with Intel’s Optane DC persistent memory. The evaluation demonstrates that our scheme boosts the overall performance by up to 50× compared with qcow2, an image format implemented in I/O virtualization, and brings almost no performance overhead compared with the native memory virtualization. The striping feature can also scale-out the virtual PM’s bandwidth performance.