migShm-openMosix Experiences

Table of Contents
Shared Memory
Building It
Stress Test
The migShm StressTest
The Application Tests
About the Author


migShm is a DSM patch for openMosix. DSM Stands for Distributed Shared Memory. It enables migration of processes that use shared memory on openMosix. DSM is being developed by the MAASK group from India. There have been some reports of migShm enabling Apache to migrate to other nodes. This evolution opens a completely new area of applications that can be clustered by openMosix.

The openMosix software package turns networked computers running GNU/Linux into a cluster. It automatically balances the load between different nodes of the cluster, and nodes can join or leave the running cluster without disruption of the service. The load is spread out among nodes according to their connection and CPU speeds.

Since openMosix is part of the kernel and maintains full compatibility with Linux, a user's programs, files, and other resources will all work as before without any further changes. The casual user will not notice the difference between a Linux and an openMosix system. To her, the whole cluster will function as one (fast) GNU/Linux system.

Currently, one of the main limitations of openMosix is that applications that use shared memory and multi-threaded applications do not migrate on the cluster. Hence applications these cannot benefit from the load-balancing features of openMosix. migShm aims to fill this need.

migShm Stands for Migration of shared memory. It's not exactly a complete DSM as of now, but is sufficient for shared memory applications to benefit from openMosix.

The idea behind this talk/paper is to find out the current state of migShm, which applications do benefit from this new step in openMosix, and how different applications react to it.

We will try to give the audience an overview of its current status with its limitations. migShm still requires a lot of users to test this environment as much as possible.