Singleton: System-wide Page Deduplication in Virtual Environments

ABSTRACT We consider the problem of providing memory-management in hypervisors and propose Singleton, a KVM-based systemwide page deduplication solution to increase memory usage efficiency. Specifically, we address the problem of doublecaching that occurs in KVM-the same disk blocks are cached at both the host(hypervisor) and the guest(VM) page-caches. Singleton's main components are identical-page sharing across guest virtual machines and an implementation of an exclusivecache for the host and guest page-cache hierarchy. We use and improve KSM-Kernel SamePage Merging to identify and share pages across guest virtual machines. We utilize guest memory-snapshots to scrub the host page-cache and maintain a single copy of a page across the host and the guests. Singleton operates on a completely black-box assumption-we do not modify the guest or assume anything about it's behaviour. We show that conventional operating system cache management techniques are sub-optimal for virtual environments, and how Singleton supplements and improves the existing Linux kernel memory management mechanisms. Singleton is able to improve the utilization of the host cache by reducing its size(by upto an order of magnitude), and increasing the cache-hit ratio(by factor of 2x). This translates into better VM performance(40% faster I/O). Singleton's unified page deduplication and host cache scrubbing is able to reclaim large amounts of memory and facilitates higher levels of memory overcommitment. The optimizations to page deduplication we have implemented keep the overhead down to less than 20% CPU utilization

A new buffer cache design exploiting both temporal and content localities

This paper presents a Least Popularly Used buffer cache algorithm to exploit both temporal locality and content locality of I/O requests. Popular data blocks are selected as reference blocks that are not only accessed frequently but also identical or similar in content to other blocks that are being accessed. Fast delta compression and decompression are used to satisfy as many I/O requests as possible using the popular reference blocks together with small deltas inside the buffer cache. The popularity of a reference block is calculated based on the statistical analysis of data contents and access frequency. A prototype LPU has been implemented as a new cache layer for Kernel Virtual Machine (KVM) on Linux system. Experimental results show LPU is effective for a variety of workloads with the maximum speed up of over 300% compared with LRU. © 2010 IEEE