Research

Recently, I developed Linux kernel driver which creates generic RAM based compressed block devices (called zram). Being RAM disks, they do not provide persistent storage but there are many use cases where persistence is not required: /tmp, various caches under /var, swap disks etc. These cases can benefit greatly from high speed RAM disks along with savings which compression brings!

However, all this seems to be completely Linux centric. But with virtualization, zram can be used for Windows too! The trick is a expose zram as a ‘raw disk’ to Windows running inside a Virtual Machine (VM). I will be using VirtualBox as example but exposing raw disks should be supported by other Virtualization solutions like VMware, KVM too.

Here is link to paper (pdf) (MP3)

Recently I came across this paper published in OSDI ‘08. Its an extension to VMware’s page-sharing and shows some amazing and hard to believe results. VMware page-sharing mechanism scans memory for all VMs and maps pages with same contents to a single page. This achieves memory savings if multiple VMs are hosted running same OS. However, with technique discussed in this paper, we find pages that are nearly same. For such pages, they save a base page and other similar pages as delta of original page. For pages which are not similar to any other page are simply compressed. Their benchmarks shows upto 45% more memory saving over ESX page-sharing under some (specially crafted) workload.