Attacking the process migration bottleneck

Moving the contents of a large virtual address space stands out as the bottleneck in process migration, dominating all other costs and growing with the size of the program. Copy-on-reference shipment is shown to successfully attack this problem in the Accent distributed computing environment. Logical memory transfers at migration time with individual on-demand page fetches during remote execution allows relocations to occur up to one thousand times faster than with standard techniques. While the amount of allocated memory varies by four orders of magnitude across the processes studied, their transfer times are practically constant. The number of bytes exchanged between machines as a result of migration and remote execution drops by an average of 58% in the representative processes studied, and message-handling costs are cut by over 47% on average. The assumption that processes touch a relatively small part of their memory while executing is shown to be correct, helping to account for these figures. Accent's copy-on-reference facility can be used by any application wishing to take advantage of lazy shipment of data.