Nswap: A network swapping module for linux clusters

Abstract

Cluster applications that process large amounts of data, such as parallel scientific or multimedia applications, are likely to cause swapping on individual cluster nodes. These applications will perform better on clusters with network swapping support. Network swapping allows any cluster node with over-committed memory to use idle memory of a remote node as its backing store and to "swap" its pages over the network. As the disparity between network speeds and disk speeds continues to grow, network swapping will be faster than traditional swapping to local disk. We present Nswap, a network swapping system for heterogeneous Linux clusters and networks of Linux machines. Nswap is implemented as a loadable kernel module for version 2.4 of the Linux kernel. It is a space-efficient and time-efficient implementation that transparently performs network swapping. Nswap scales to larger clusters, supports migration of remotely swapped pages, and supports dynamic growing and shrinking of Nswap cache (the amount of RAM available to store remote pages) in response to a node's local memory needs. Results comparing Nswap running on an eight node Linux cluster with 100BaseT Ethernet interconnect and faster disk show that Nswap is comparable to swapping to local, faster disk; depending on the workload, Nswap's performance is up to 1.7 times faster than disk to between 1.3 and 4.6 times slower than disk for most workloads. We show that with faster networking technology, Nswap will outperform swapping to disk. © Springer-Verlag 2003.