Interestingly, KeyKOS's successors ended up removing the transparent checkpointing out of the kernel. As I understand it the reasoning was two fold. 1) virtua

Interestingly, KeyKOS's successors ended up removing the transparent checkpointing out of the kernel. As I understand it the reasoning was two fold. 1) virtual memory page outs can be implemented cleanly by a user space process, so pushing it out there makes the kernel have a smaller surface area. 2) checkpointing in distributed envs requires some idea of the checkpoint event being propagated to user space since there's all sorts of state that could be on other systems. Rolling back is going to get TCP, etc out of sync. The earlier user space knows it's been rolled back to a checkpoint, the quicker it can recover practically.