Improving Virtualized Storage Performance with Sky.

We introduce Sky, an extension to the VMM that gathers insights and information by intercepting system calls made by guest applications. We show how Sky gains three specific insights -- guest file-size information, metadata-data distinction, and file-content hints -- and uses said information to enhance virtualized-storage performance. By caching small files and metadata with higher priority, Sky reduces the runtime by 2.3 to 8.8 times for certain workloads. Sky also achieves 4.5 to 18.7 times reduction in the runtime of an open-source block-layer deduplication system by exploiting hints about file contents. Sky works underneath both Linux and FreeBSD guests, as well as under a range of file systems, thus enabling portable and general VMM-level optimization underneath a wide range of storage stacks.