> Subject: Re: [RFC qemu 0/4] A PV solution for live migration optimization > > * Liang Li (liang.z...@intel.com) 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. > 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? > Only detect the unmapped/zero mapped pages is not enough. Consider the situation like case 2, it can't achieve the same result. > > This RFC version doesn't take the post-copy and RDMA into > > consideration, maybe both of them can benefit from this PV solution by > > with some extra modifications. > > For postcopy to be safe, you would still need to send a message to the > destination telling it that there were zero pages, otherwise the destination > can't tell if it's supposed to request the page from the source or treat the > page as zero. > > Dave I will consider this later, thanks, Dave. Liang > > > > > Performance data > > ================ > > > > Test environment: > > > > CPU: Intel (R) Xeon(R) CPU ES-2699 v3 @ 2.30GHz Host RAM: 64GB > > Host Linux Kernel: 4.2.0 Host OS: CentOS 7.1 > > Guest Linux Kernel: 4.5.rc6 Guest OS: CentOS 6.6 > > Network: X540-AT2 with 10 Gigabit connection Guest RAM: 8GB > > > > Case 1: Idle guest just boots: > > ============================================ > > | original | pv > > ------------------------------------------- > > total time(ms) | 1894 | 421 > > -------------------------------------------- > > transferred ram(KB) | 398017 | 353242 > > ============================================ > > > > > > Case 2: The guest has ever run some memory consuming workload, the > > workload is terminated just before live migration. > > ============================================ > > | original | pv > > ------------------------------------------- > > total time(ms) | 7436 | 552 > > -------------------------------------------- > > transferred ram(KB) | 8146291 | 361375 > > ============================================ > >
