Lightweight process migration and memory prefetching in openMosix

We propose a lightweight process migration mechanism and an adaptive memory prefetching scheme called AMPoM (adaptive memory prefetching in openMosix), whose goal is to reduce the migration freeze time in openMosix while ensuring the execution efficiency of migrants. To minimize the freeze time, our system transfers only a few pages to the destination node during process migration. After the migration, AMPoM analyzes the spatial locality of memory access and iteratively prefetches memory pages from remote to hide the latency of inter-node page faults. AMPoM adopts a unique algorithm to decide which and how many pages to prefetch. It tends to prefetch more aggressively when a sequential access pattern is developed, when the paging rate of the process is high or when the network is busy. This advanced strategy makes AMPoM highly adaptive to different application behaviors and system dynamics. The HPC Challenge benchmark results show that AMPoM can avoid 98% of migration freeze time while preventing 85-99% of page fault requests after the migration. Compared to openMosix which does not have remote page fault, AMPoM induces a modest overhead of 0-5% additional runtime. When the working set of a migrant is small, AMPoM outperforms openMosix considerably due to the reduced amount of data transfer. These results indicate that by exploiting memory access locality and prefetching, process migration can be a lightweight operation with little software overhead in remote paging.