On Thu, Dec 17, 2020 at 07:57:07PM +0300, Andrey Gruzdev wrote: > This patch series is a kind of 'rethinking' of Denis Plotnikov's ideas he's > implemented in his series '[PATCH v0 0/4] migration: add background snapshot'. > > Currently the only way to make (external) live VM snapshot is using existing > dirty page logging migration mechanism. The main problem is that it tends to > produce a lot of page duplicates while running VM goes on updating already > saved pages. That leads to the fact that vmstate image size is commonly > several > times bigger then non-zero part of virtual machine's RSS. Time required to > converge RAM migration and the size of snapshot image severely depend on the > guest memory write rate, sometimes resulting in unacceptably long snapshot > creation time and huge image size. > > This series propose a way to solve the aforementioned problems. This is done > by using different RAM migration mechanism based on UFFD write protection > management introduced in v5.7 kernel. The migration strategy is to 'freeze' > guest RAM content using write-protection and iteratively release protection > for memory ranges that have already been saved to the migration stream. > At the same time we read in pending UFFD write fault events and save those > pages out-of-order with higher priority. > > How to use: > 1. Enable write-tracking migration capability > virsh qemu-monitor-command <domain> --hmp migrate_set_capability. > track-writes-ram on > > 2. Start the external migration to a file > virsh qemu-monitor-command <domain> --hmp migrate exec:'cat > ./vm_state' > > 3. Wait for the migration finish and check that the migration has completed. > state.
For the rest patches: Acked-by: Peter Xu <pet...@redhat.com> Dave, considering the live snapshot series has been dangling for quite some time upstream (starting from Denis's work), do you have plan to review/merge it in the near future? I believe there're still quite a few things missing, but imho most of them should be doable on top too. Thanks! -- Peter Xu
