Virtio based Transcendent Memory

Virtualization is a technology that lets you run multiple virtual machines on a single physical machine, by sharing the resources of that single computer across the virtual machines. While CPU, I/O devices and other resources are easily shared among the virtual machines, sharing of physical memory is much more difficult. Memory Management mechanisms such as Ballooning and Hotplug Memory are widely used in virtualization systems for efficient utilization of RAM, but digging deep they have their own set of problems. Therefore, memory is increasingly becoming a bottleneck in virtualization. Transcendent Memory (tmem) is a new approach to efficie-ntly utilize physical memory in a virtual environment. Transcendent Memory makes optimal use of memory that is being "Underutilized" by a virtual machine. "Unassigned" memory that otherwise goes waste is also utilized. While working in complement to Ballooning, tmem also successfully solves the issues arising due to Ballooning. This technique has been implemented, and proved on Xen. It was presented in OLS 2009 by Dan Magenheimer. We have implemented this technique, in a more generic framework, using the Virtio device driver model. Virtio model, is an efficient, well maintained set of linux drivers, which can be adapted for various different hypervisor implementations using a shim layer. This framework is supported by hypervisors like KVM, and lguest. With this implementation, this technique is easily portable to these hypervisors. This paper discusses a few scenarios which motivate us towards this approach. After a brief discussion of the technique, we delve into details about Virtio Model, before explaining Tmem operations, and the actual implementation in detail.