Re: [Xen-devel] [PATCH v3 1/3] libxl: xl mem-max et consortes must update static-max in xenstore too

[Daniel Kiper <daniel.kiper@xxxxxxxxxx>]

On Tue, Apr 09, 2013 at 03:18:10PM +0100, Ian Jackson wrote:
> Daniel Kiper writes ("Re: [Xen-devel] [PATCH v3 1/3] libxl: xl mem-max et 
> consortes must update static-max in xenstore too"):
> > On Tue, Apr 09, 2013 at 02:10:53PM +0100, Ian Jackson wrote:
> > > The reason for xl using static-max is that in the absence of memory
> > > hotplug, attempting to raise a guest above static-max will not work.
> > > And this check takes effect in xl.
> >
> > OK but now it is quiet difficult (or close to impossible) to know
> > in advance that a given guest supports memory hotplug or not.
>
> Right.
>
> > That is why I think that static-max should be unconditionally
> > changed or the guest should write something in xenstore to inform
> > that it supports memory hotplug and relevant check should be waived.
>
> Right.  I don't see what any of that has to do with "xl mem-max"
> though.  The purpose of xl mem-max is to update the guest's
> enforcement limit.

...and static-max if you would like to use memory hotplug in real.
If not, then xl mem-set does not allow you to allocate more memory
to a guest than static-max.

> I think it would be great for the guest to write something to xenstore
> saying it supports memory hotplug.  How does the protocol work ?  The
> guest writes "I support memory hotplug", and the tools then ignore

More or less...

> static-max and simply update the memory target with a new value ?  Do
> the tools need to do anything else ?

I think that tools should not ignore static-max in any casy.
Memory target should not be never ever above static-max.

Daniel

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