If you just pull things on demand, you're going to get a lot of round-trip-time penalties to page things in.
I think you should still be pushing the memory as fast as you can, but maybe you start the child while this is still in progress, and prioritize sending stuff the child asks for (reorder to send that stuff "next"), if you've not already sent it.
Yah that is indeed a super important optimization for avoiding round trips. CRIU does this and calls it "pre-paging", their wiki also mentions that they adapt their page streaming to try to pre-stream pages around pages that have been faulted: https://en.wikipedia.org/wiki/Live_migration#Post-copy_memor...
edit: lol I didn't realized that isn't CRIU's wiki since they just linked to a Wikipedia page and both use WikiMedia software. This is the actual CRIU wiki page, and it's way harder to tell if they do this, although I suspect they do and it's in the "copy images" step of the diagram https://criu.org/Userfaultfd
That’s a great idea. One of my thoughts was to “pre-heat” the process by executing a bit locally with side effects disabled to see what would get immediately accessed and send that first.
If your systems strictly match somehow (machine image with auto update disabled? or regularly hash and timestamp files on both systems) you can also cheat by mapping some of the files locally on the other side.
I think you should still be pushing the memory as fast as you can, but maybe you start the child while this is still in progress, and prioritize sending stuff the child asks for (reorder to send that stuff "next"), if you've not already sent it.