On Fri, Mar 04, 2016 at 02:32:47PM +0530, Jitendra Kolhe wrote: > Even though the pages which are returned to the host by virtio-balloon > driver are zero pages, the migration algorithm will still end up > scanning the entire page ram_find_and_save_block() -> ram_save_page/ > ram_save_compressed_page -> save_zero_page() -> is_zero_range(). We > also end-up sending some control information over network for these > page during migration. This adds to total migration time.
I wonder if it is the scanning for zeros or sending the whiteout which affects the total migration time more. If it is the former (as I would expect) then a rather local change to is_zero_range() to make use of the mapping information before scanning would get you all the speedups without protocol changes, interfering with postcopy etc. Roman.
