RE: [Xen-devel] can't create any more pv-on-hvm domains after~38under 3.3-testing

["James Harper" <james.harper@xxxxxxxxxxxxxxxx>]

> On 03/12/2008 11:27, "James Harper" <james.harper@xxxxxxxxxxxxxxxx>
wrote:
> 
> > Alternatively it could be a combination of the gplpv drivers and
netback
> > or blkback. I'm pretty sure that I had the problem before I started
> > testing pvscsi...
> >
> > The machine I am testing on will be busy for the rest of the night,
but
> > tomorrow I'll do some testing and see what happens, unless you can
> > suggest a way I could discover what those pages belong to in the
> > meantime?
> 
> Unfortunately it's a bit of a pain in the butt since we don't have
full
> page
> tracking in Xen -- we only know that *someone* *somewhere* has that
page
> mapped for *some* purpose. Indeed even with more tracking Xen can only
> really tell you which domain holds the reference, and that's bound to
be
> dom0 (unless this is a bogus refcounting bug in Xen itself).
> 
> I would suggest dumping addresses of interesting control pages in your
> backend drivers (some can log that already if built with debugging I
> think),
> then match up the address of the remaining page in the zombie domain.
> 

So just to clarify, would this be a page which has been granted in a
DomU's grant table and then either given to Dom0 via an entry in xenbus
or via a ringbuffer request? The former seems more likely as I wouldn't
have thought that there would be a request in flight every single time,
and then probably not only a single request.

And it wouldn't be any use me dumping DomU's 'PFN' either would it? As
that would be different to the real physical PFN...

I'm using a kernel from Debian (that may be the cause of the problem in
itself actually...) which is 2.6.18 and claims to have the 3.3 patches
applied. I might pursue that angle first. Blkback and netback are
compiled into the kernel which makes debugging a bit harder.

James

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