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 t

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_memory_migration 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 https://criu.org/Userfaultfd