[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] yanked share, round 2
> Hi Keir, I'm not familiar enough with zombie anatomy to help there, so let > me try this reasoning: today's Xen architecture cannot promise that a > shared page can ever be returned to normal, non-shared service. Thus, any > DomU that routinely creates shared pages *must* eventually run out of > memory. Eveni if it could reboot, causing the control tools to allocate it new memory... the more worrying problem is that a domain that does *not* return shared pages could eventually end up holding all the memory in the machine, with it all being credited to other (zombie) domains. > Of course if all DomU's try to play nice, it would take a long > while. We still face a snag in which Xen allows DomU bugs, DomU crashes > and DomU evil to accumulate over time. By analogy to the hardware world, a > PCI device that could not promise to let go of pages would be unacceptable. A centralised store (managed by a trusted entity) would be rather good for domUs that really don't trust each other. It'd be worth having a driver that could set these up - presumably with shares advertised using XenStore. Cheers, Mark > -steve > > > > -----Original Message----- > From: Keir Fraser [mailto:Keir.Fraser@xxxxxxxxxxxx] > Sent: Friday, January 13, 2006 11:21 AM > To: King, Steven R > Cc: xen-devel@xxxxxxxxxxxxxxxxxxx > Subject: Re: [Xen-devel] yanked share, round 2 > > > On 13 Jan 2006, at 19:07, King, Steven R wrote: > > > > The purpose of the under-page is to plug the memory hole in the remote > > DomU created by a surprise unsharing. A nervous remote DomU could > > check that a share is GTF_safe before proceeding to map the page. > > > > Good, bad or ugly? > > What's wrong with the current scheme (sharing domU sticks around as a > zombie until foreign mappings disappear)? This needn't stop control tools > from restarting the domain (they can see that it has shut down, for > example, and is simply awaiting reaping when its refcnt falls to zero). > > It's arguable the zombies needn't even be kept on the domain list, so they > become invisible to the control tools (since they're really just a resource > container for foreign page mappings). OTOH hiding things from control tools > is probably a bad idea. :-) > > -- Keir > > _______________________________________________ > Xen-devel mailing list > Xen-devel@xxxxxxxxxxxxxxxxxxx > http://lists.xensource.com/xen-devel -- Dave: Just a question. What use is a unicyle with no seat? And no pedals! Mark: To answer a question with a question: What use is a skateboard? Dave: Skateboards have wheels. Mark: My wheel has a wheel! _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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