[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] RE: [Xen-devel] [Question] How to support page offline in Xen environment
Tim Deegan <mailto:Tim.Deegan@xxxxxxxxxx> wrote: > At 18:30 +0800 on 03 Dec (1228329001), Jiang, Yunhong wrote: >> a) A page is foreign mapped by another guest (e.g. dom0), > change p2m entries is not enough. > > True. > >> b) A page is assigned to a domain with device assigned, we > can't simply change the p2m entry because of DMA operation may > on-going. (this in fact can't resolve cleanly through live > migration, although the tools do hot remove in advance). > > That seems to be orthogonal to the question of how the page is got rid > of; you can do a hot remove and hot add whether you do a full live-migrate > or not. > >> c) If a page is used like shadow page table or, virutal > local apic's page, currently we can't simply exchange these pages. > > True, but live-migration doesn't help that because right now given an > MFN that's in use as a shadow page or any HVM state page you can't > easily find out which domain is responsible for it. Ahh, yes, didn't realize this. So do you think it is ok to add such information? > > Also, remember that full live-migration needs enough spare RAM to hold > an extra copy of the guest, so it couldn't work on guests larger than > half the physical RAM, for example. Yes, that is one argument we thought that before. > >> d) For PV guest, can this be done without co-operation from guest? > > Yes it can. As long as you don't use the "fast path" resume to restart > the guest, it will re-read its p2m just like it would after a full > save/restore. What do you mean of the "fast path"? > >> Of course, we can simplify the request, for example, no > support for page in item a), b) and c) and that will be ok. >> That's the reason we hope to get suggestion on next step. > > I think it depends on how important it is to be able to offline frames > quickly and transparently. If that's not important, then just save the > owning domain to disk, offline the frames, and restore it. If it is > important, I'd be inclined to to something very lightweight based on > small parts of the save/restore code (which will be much faster than > live migration), and keep save-to-disk as a backstop for the > edge cases. Do you mean the "something very lightweight based on small parts of the save/restore code" is done in management tools, not in HV, am I right? Thanks Yunhong Jiang > > Tim. > > -- > Tim Deegan <Tim.Deegan@xxxxxxxxxx> > Principal Software Engineer, Citrix Systems (R&D) Ltd. > [Company #02300071, SL9 0DZ, UK.] _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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