Sunday, September 11, 2011
Network RAM enables nodes with over-committed memory to swap pages over the network, storing them in the idle RAM of other nodes and avoiding swapping to slow, local disk.
As several parallel or parallel and sequential applications are simultaneously running on the system ,there are likely to be imbalances in RAM usage across nodes. Network RAM systems take advantage of imbalances in RAM usage and allow nodes with over-committed RAM to locate and use the idle RAM of remote nodes as backing store; pages are “swapped out” over a fast network and stored in the idle RAM of other nodes. This disparity will likely continue to grow because disk speeds are limited by mechanical movement.
Large amounts of idle cluster memory are almost always available (even when some nodes are overloaded), and that large chunks are available for significant amounts of time. As a result, a Network RAM system should be able to find usable amounts of idle RAM to store swapped pages.
Nswap is a Network RAM system for general purpose Linux clusters and networked systems. Cluster applications that process large amounts of data, such as parallel scientific or multimedia applications, are likely to cause disk swapping on individual cluster nodes.
Cluster applications that process large amounts of data, such as parallel scientific or multimedia applications, are likely to cause swapping on individual cluster nodes.
Nswap is implemented as a loadable kernel module that runs entirely in kernel space on an unmodified Linux 2.6 kernel. It transparently and efficiently provides network RAM to cluster applications. Nswap uses a peer-to-peer design (vs. a centralized system) that scales to large clusters. A novel feature of Nswap is its adaptability to changes in a node's memory load; when a node needs more memory for its local processes, it acts as an Nswap client swapping its pages over the network, and when a node has idle RAM space it acts as an Nswap server caching other nodes' swapped pages.
Ref: Reliable Adaptable Network RAM, Swarthmore College, USA.