Reference history, page size, and migration daemons in local/remote architectures

We address the problem of paged main memory management in the local/remote architecture subclass of shared memory multiprocessors. We consider the case where the operating system has primary responsibility and uses page migration as its main tool. We identify some of the key issues with respect to architectural support (reference history maintenance, and page size), and operating system mechanism (duration between daemon passes, and number of migration daemons). The experiments were conducted using software implemented page tables on 32-node BBN Butterfly Plus#8482;. Several numeral programs with both synthetic and real data were used as the workload. The primary conclusion is that for the cases considered migration was at best marginally effective. On the other hand, practical migration mechanisms were robust and never significantly degraded performance. The specific results include: 1) Referenced bits with aging can closely approximate Usage fields, 2) larger page sizes are beneficial except when the page is large enough to include locality sets of two processes, and 3) multiple migration daemons can be useful. Only small regions of the space of architectural, system, and workload parameters were explored. Further investigation of other parameter combinations is clearly warranted.