For process tree migration, the biggest part of transfer data is the memory used by the processes. Therefore, optimizing this memory transfer would have the most benefit.
Without the page server, migrating the user memory pages consists of:
- dumping the memory to files on disk;
- copying the files over network to the destination system;
- restoring by reading the files into memory.
Such a process incurs significant I/O overhead and slows down the migration. This overhead can be avoided by doing a direct memory to memory copy, avoiding any disk I/O.