Re: [Xen-devel] can not use all available memory

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2012-11-23 at 13:29 +0000, Pasi KÃrkkÃinen wrote:
> On Fri, Nov 23, 2012 at 01:15:53PM +0000, Ian Campbell wrote:
> > On Fri, 2012-11-23 at 12:55 +0000, Pasi KÃrkkÃinen wrote:
> > 
> > > > This has been discussed at length on the list before, please check the
> > > > archives.
> > > > 
> > > 
> > > I tried googling quickly but I didn't find anything relevant..
> > 
> > I found
> > http://web.archiveorange.com/archive/v/zCKz5T3PLvtyZDSPQc9i
> > in a matter of seconds, then:
> > http://lists.xen.org/archives/html/xen-devel/2011-11/msg01415.html
> > http://lists.xen.org/archives/html/xen-users/2012-05/msg00139.html
> > http://lists.xen.org/archives/html/xen-users/2012-05/msg00146.html
> > 
> > > To me this behaviour still seems wrong. What's the point of autoballoon=1 
> > > trying to 
> > > balloon down dom0 if the hypervisor already has enough free memory for 
> > > the VM ? 
> > > 
> > > In this case:
> > >   - dom0_mem=2G
> > >   - new VM to launch with size 16 GB.
> > >   - Xen has 28 GB of free memory.
> > > 
> > > So clearly there's no need to try to balloon down dom0.. 
> > 
> > Right, so don't set autoballoon then.
> > 
> 
> It's enabled as a default.. so many people hit this problem.
> 
> 
> > > not-yet-implemented check/feature in xl, or a bug? 
> > 
> > Neither, it is the intended behaviour of xl autoballoon, this option
> > means exactly "take the required memory from dom0".
> > 
> 
> http://xenbits.xen.org/docs/4.2-testing/man/xl.conf.5.html
> 
> "autoballoon=BOOLEAN
> 
>     If disabled then xl will not attempt to reduce the amount of
> memory assigned to domain 0 in order to create free memory when
> starting a new domain. You should set this if you use the dom0_mem
> hypervisor command line to reduce the amount of memory given to domain
> 0 by default.
> 
>     Default: 1"
> 
> 
> I think we should modify that to say "You should set autoballoon=0 if you use 
> the dom0_mem hypervisor command line .." 
> At least I understood that text in the opposite way..

Yes, there should be a s/set/unset/ in there I think.

> Also: What happens if you have autoballoon=1 and you start some VMs, then 
> stop the VMs, 
> so most of the memory is now free in Xen.. 

xl balloons dom0 back up when it destroy domains with autoballoon=1.

> and then you try to start a big VM ? 
> Aren't you going to hit the same problem as in this thread? 
> 
> 
> -- Pasi
> 



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