Fast Virtual Machine Resume for Agile Cloud Services

Resuming virtual machines is an important management operation in the virtualized data center. (Re)-instantiating VMs as quickly as possible helps to combat flash crowds and provide true on-demand services. Unfortunately, resuming a VM currently takes tens of seconds, depending on the VM´s size and available disk I/O bandwidth. Because it is not strictly necessary to read the entire state from disk to continue executing the VM instance, we propose an on-demand resume feature. Instead of indiscriminately reading the entire state from disk, we utilize the host OS´s support for lazily reading pages from disk only when they are needed. We have implemented our idea as part of the open-source, virtual machine emulator qemu. Our idea required to modify less than 100 lines of code. The experimental evaluation of our on-demand resume feature reveals that it works as expected: resume times no longer depend on the VM´s total state but rather on the actively used state. We are able to resume instances with multiple gigabytes of state in as little as 3 seconds, i.e., we reduced the resume time to less than 1/10th compared to the default implementation.