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Tsirkin" , Markus Armbruster , Alexander Duyck , qemu-devel@nongnu.org, Paolo Bonzini , Den Lunev , "Dr . David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" >>> Anyhow I'm quite sure that adding global MISSING handler for snapshotting >>> is too heavy and not really needed. >> UFFDIO_ZEROCOPY installs a zero pfn and that should be all of it. There'll >> definitely be overhead, but it may not be that huge as imagined. Live snapshot >> is great in that we have point-in-time image of guest without stopping the >> guest, so taking slightly longer time won't be a huge loss to us too. >> >> Actually we can also think of other ways to work around it. One way is we can >> pre-fault all guest pages before wr-protect. Note that we don't need to write >> to the guest page because read would suffice, since uffd-wp would also work >> with zero pfn. It's just that this workaround won't help on saving snapshot >> disk space, but it seems working. It would be great if you have other >> workarounds, maybe as you said UFFDIO_ZEROCOPY is not the only route. >> >> Thanks, >> > Just to add: one of the good options is too keep track of virtio-baloon discarded pages and > pre-fault them before migration starts. What do you think? Just pre-fault everything and inhibit the balloon. That should work. -- Thanks, David / dhildenb