Checkpoint/restart: it's complicated

linux-cr does the former using its objhash so that we don't checkpoint shared state more than once. It avoids doing disk IO by, whenever possible. not bundling file/directory contents into the checkpoint image (generic_file_checkpoint()). Instead it relies on userspace to do IO-bandwidth friendly optimizations like using filesystem snapshots.

That said, file "contents" are necessary for anon_inode-based interfaces such as eventfd, epoll, signalfd, and timerfd because those can't be "backed up" and restored like normal files.