Re: [Xen-devel] Is it possiable to use domU's balloon in dom0 user program?

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

> From: Ian Campbell [mailto:Ian.Campbell@xxxxxxxxxx]
> Subject: Re: [Xen-devel] Is it possiable to use domU's balloon in dom0 user 
> program?
> 
> On Thu, 2013-04-18 at 03:45 +0100, Dan Magenheimer wrote:
> > > From: Ian Campbell [mailto:Ian.Campbell@xxxxxxxxxx]
> > > Sent: Monday, April 15, 2013 3:19 AM
> > > To: Demon King
> > > Cc: xen-devel@xxxxxxxxxxxxx
> > > Subject: Re: [Xen-devel] Is it possiable to use domU's balloon in dom0 
> > > user program?
> > >
> > > On Sat, 2013-04-13 at 11:21 +0100, Demon King wrote:
> > > > Our team want designed a program in dom0 to control vm's memory
> > > > through balloon, such as to increasing balloon memery of vm1 and then
> > > > other vm will use it later. Is it possiable to do this?Thank you!
> > >
> > > I'm not 100% what you are asking but if you are asking if you can reduce
> > > a domain's memory with ballooning and the subsequently (either
> > > immediately or later) increase the memory allocation of another domain
> > > using that slack memory then the answer is yes.
> > >
> > > The only constraint is that in the absence of memory hotplug (which is
> > > present in mainline kernels but not AFAIK support yet by most
> > > toolstacks) you cannot balloon a guest up to more than its original
> > > memmax= value, note that it is possible to boot a PV domain with less
> > > current allocation than its maxmem ("preballooned") and using PoD and
> > > suitable PV drivers the same can be done with some types of HVM guest.
> >
> > Any chance you are trying to do what xenballoond does?  See
> > the source tree under tools/xenballoon (or google "xenballoond.README").
> > Note that this code is five years old, is distro dependent, and is now
> > completely unsupported.  It was the first step toward transcendent
> > memory, which has replaced it.
> 
> Should we be removing it then?
> 
> Like so:

Perhaps.  I'd like to get Konrad's opinion first.

This kind of question seems to come up about once a year and its
existence in the tree serves as a good example of what can be
done with ballooning in legacy/unmodified Linux guests (e.g.
shows how to write to the balloon driver via sysfs).

So I'll defer to your decision if Konrad agrees.

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