Adaptive and Reliable Paging to Remote Main Memory

Workstation clusters provide significant aggregate amounts of resources, including processing power and main memory. In this paper we explore the collective use of main memory in a workstation cluster to boost the performance of applications that require more memory than a single workstation can provide. We describe the design, simulation, implementation, and evaluation of a pager that uses main memory of remote workstations in a workstation cluster as a faster-than-disk paging device and provides reliability in case of single workstation failures and adaptivity in network and disk load variations. Our pager has been implemented as a block device driver linked to the Digital UNIX operating system, without any modifications to the kernel code. Using several test applications we measure the performance of remote memory paging over an Ethernet interconnection network and find it to be up to twice as fast as traditional disk paging. We also evaluate the performance of various reliability policies and demonstrate their feasibility even over low bandwith networks such as Ethernet. We conclude that the benefits of reliable remote memory paging in workstation clusters are significant today and are likely to increase in the near future.