On Thu, Apr 13, 2017 at 01:44:11PM -0700, Matthew Wilcox wrote: > On Thu, Apr 13, 2017 at 05:35:03PM +0800, Wei Wang wrote: > > 2) transfer the guest unused pages to the host so that they > > can be skipped to migrate in live migration. > > I don't understand this second bit. You leave the pages on the free list, > and tell the host they're free. What's preventing somebody else from > allocating them and using them for something? Is the guest semi-frozen > at this point with just enough of it running to ask the balloon driver > to do things?
There's missing documentation here. The way things actually work is host sends to guest a request for unused pages and then write-protects all memory. So guest isn't frozen but any changes will be detected by host.
