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Re: [Xen-devel] [PATCH] x86: fix improper return value from relinquish_m

To: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] x86: fix improper return value from relinquish_memory()
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Wed, 24 Mar 2010 14:54:54 +0000
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On 24/03/2010 14:43, "Konrad Rzeszutek Wilk" <konrad.wilk@xxxxxxxxxx> wrote:

>> 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.

There's a big difference between a zombie domain owning a few pages versus a
zombie domain still having most of its memory, though. One could be a
ref-count leak, the other sounds potentially like something wrong with the
domain-killing routines (not that there's enough data to definitely say
either way for sure yet -- but at least they do sound like different bugs).

 -- Keir

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