Re: [PATCH] x86: fix improper return value from relinquish_memory()

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Wed, Mar 24, 2010 at 11:23:32AM +0000, Jan Beulich wrote:
> >>> "Jan Beulich" <JBeulich@novell.com> 24.03.10 12:07 >>>
> >While apparently only a theoretical possibility (domain_kill() has a
> >BUG_ON() that wasn't reported to trigger so far), I still think it is
> >better to have the code cleaned up.
> 
> Btw., the reason I was looking at that code was that we observe
> zombie domains - ones in DOMDYING_dead state, perhaps having
> almost none of their memory freed (shadowed guests appear to be
> particularly bad). In one of the reports, an interesting extra fact
> was that this happened only for the first 100 guests - any
> subsequent ones got destroyed properly (obviously to get there
> this requires quite a bit of memory in the host). Has anyone else
> observed this? Does this ring any bells?

Yes.
http://lists.xensource.com/archives/html/xen-devel/2008-12/msg00222.html

B/c of the page count we had guests that would never have their mmap
count removed causing them to be zombie guests. Our fix, which wasn't
nice, was to have the guest domain id re-number and shove it and its
remaining page ownership (at that point it only has some pages in Dom0
and DomU) in a corner.