> On 3/8/2016 4:44 PM, Amit Shah wrote: > > On (Fri) 04 Mar 2016 [15:02:47], Jitendra Kolhe 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. > >>>> > >>> > >>> Ooh, different solutions for the same purpose, and both based on the > balloon. > >> > >> We were also tying to address similar problem, without actually > >> needing to modify the guest driver. Please find patch details under mail > with subject. > >> migration: skip sending ram pages released by virtio-balloon driver > > > > The scope of this patch series seems to be wider: don't send free > > pages to a dest at all, vs. don't send pages that are ballooned out. > > > > Amit > > Hi, > > Thanks for your response. The scope of this patch series doesn’t seem to > take care of ballooned out pages. To balloon out a guest ram page the guest > balloon driver does a alloc_page() and then return the guest pfn to Qemu, so > ballooned out pages will not be seen as free ram pages by the guest. > Thus we will still end up scanning (for zero page) for ballooned out pages > during migration. It would be ideal if we could have both solutions. > Agree, for users who care about the performance, just skipping the free pages. For users who have already turned on virtio-balloon, your solution can take effect. Liang > Thanks, > - Jitendra _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
