Re: [Xen-devel] [Question] How to support page offline in Xen environment

[Tim Deegan <Tim.Deegan@xxxxxxxxxx>]

At 23:21 +0800 on 11 Dec (1229037698), Jiang, Yunhong wrote:
> Tim, do you think this code path will keep guest's service continue
> (that's one reason we considered LM method before). Seems from the
> code, the guest will be down for very short time, but I'm not qutie
> sure. I'm still trying to reading the code.

Yes; the resume code was written as part of a project that does
continuous live snapshotting of a running guest to provide
fault-tolerance.  The downtime for offlining pages this way should be
even less than for live migration.

Cheers,

Tim.

> Thanks
> Yunhong Jiang
> 
> xen-devel-bounces@xxxxxxxxxxxxxxxxxxx <> wrote:
> >> Have a look at the code for xc_domain_resume in libxc/xc_resume.c.  The
> >> slow-and-safe version makes the domain state look like it would after a
> >> save/restore, so that older kernels can be resumed after they've paused
> >> and had their state saved.  The fast version just changes the return
> >> code that the guest will see from its shutdown hypercall.
> >> 
> >> My suggestion is that you cause the guest to stop like it would for a
> >> save to disk, shuffle its p2m around, and call the slow-path resume
> >> function so that it will pick up the new p2m properly.
> > 
> > I will dig-into the code  Thanks for your suggestion.
> > 
> >> 
> >>> 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?
> >> 
> >> Yes.  For the common case this lets you get what you want without the
> >> hypervisor being involved.
> > 
> > So maybe the policy can be: if HV can offline page easily
> > (like page owned by hvm domain without device assigned, or
> > free pages), HV will do that, otherwise, we will leave it to user space
> > tools. 
> > 
> > We will firstly implement the code in HV side.
> > 
> >> 
> >> Cheers,
> >> 
> >> Tim.
> >> 
> >> --
> >> Tim Deegan <Tim.Deegan@xxxxxxxxxx>
> >> Principal Software Engineer, Citrix Systems (R&D) Ltd.
> >> [Company #02300071, SL9 0DZ, UK.]
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-- 
Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, Citrix Systems (R&D) Ltd.
[Company #02300071, SL9 0DZ, UK.]

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