> On Thu, Mar 03, 2016 at 05:46:15PM +0000, Dr. David Alan Gilbert wrote: > > * Liang Li (liang.z.li@xxxxxxxxx) wrote: > > > The current QEMU live migration implementation mark the all the > > > guest's RAM pages as dirtied in the ram bulk stage, all these pages > > > will be processed and that takes quit a lot of CPU cycles. > > > > > > From guest's point of view, it doesn't care about the content in > > > free pages. We can make use of this fact and skip processing the > > > free pages in the ram bulk stage, it can save a lot CPU cycles and > > > reduce the network traffic significantly while speed up the live > > > migration process obviously. > > > > > > This patch set is the QEMU side implementation. > > > > > > The virtio-balloon is extended so that QEMU can get the free pages > > > information from the guest through virtio. > > > > > > After getting the free pages information (a bitmap), QEMU can use it > > > to filter out the guest's free pages in the ram bulk stage. This > > > make the live migration process much more efficient. > > > > Hi, > > An interesting solution; I know a few different people have been > > looking at how to speed up ballooned VM migration. > > > > I wonder if it would be possible to avoid the kernel changes by > > parsing /proc/self/pagemap - if that can be used to detect > > unmapped/zero mapped pages in the guest ram, would it achieve the > same result? > > Yes I was about to suggest the same thing: it's simple and makes use of the > existing infrastructure. And you wouldn't need to care if the pages were > unmapped by ballooning or anything else (alternative balloon > implementations, not yet touched by the guest, etc.). Besides, you wouldn't > need to synchronize with the guest. > > Roman. The unmapped/zero mapped pages can be detected by parsing /proc/self/pagemap, but the free pages can't be detected by this. Imaging an application allocates a large amount of memory , after using, it frees the memory, then live migration happens. All these free pages will be process and sent to the destination, it's not optimal. Liang _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
