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Re: [Xen-devel] 3.0.5-rc3: Creating HVM guest fails with: Cannot allocate memory

On Fri, Apr 27, 2007 at 07:53:24AM +0100, Keir Fraser wrote:
> On 27/4/07 00:12, "Daniel P. Berrange" <berrange@xxxxxxxxxx> wrote:
> > The _constructDomain call is failing in xc.domain_create() - the code which
> > deals with ballooning down Domain-0 is not even run yet - that lives in
> > the _initDomain method. So HVM domain creation is failing before XenD has
> > even had a chance to do ballooning. If I manually use 'xm mem-set' to
> > balloon down Domain-0 ahead of time, everything works just fine.
> > 
> > I'm at a lose to figure out how to solve this without major re-arranging
> > of the order of _constructDomain & _initDomain work. Perhaps someone can
> > figure out an easier fix ?
> I don't think domain_create() allocates very many pages, although it's
> possible it's making a default allocation of shadow memory. Assuming not, it
> may be sufficient to make auto-balloon leave a bit of slack memory rather
> than try to account for all available memory down to the last page. A few
> pages might turn out to suffice. Does this problem occur with the very first
> domain you try to create after booting the machine?

It seems to occurr with any HVM guest I try to create, unless there was already
some free mem (from starting & stopping a previous dom). I'm testing with this
very simple hack which seems to make it work - just ensure the balloon driver
frees a 10 MB chunk right at the start. Hardcoding is fine because when we
later get to the _initDomain() method we'll definitely be freeing up much
more than 10 MB for the HVM guests's actual mem requirements.

--- xen-3.0.5-testing.hg-rc3-14934/tools/python/xen/xend/XendDomainInfo.py      
2007-04-26 19:30:11.000000000 -0400
+++ xen-3.0.5-testing.hg-rc3-14934.new/tools/python/xen/xend/XendDomainInfo.py  
2007-04-26 19:36:06.000000000 -0400
@@ -1422,6 +1422,8 @@ class XendDomainInfo:
                 raise VmError("HVM guest support is unavailable: is VT/AMD-V "
                               "supported by your CPU and enabled in your "
+            # Hack to pre-reserve some mem for basic HVM setup
+            balloon.free(10*1024)
         self.domid = xc.domain_create(
             domid = 0,

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