Re: [Xen-devel] long latency of domain shutdown

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

>>> Keir Fraser <keir.fraser@xxxxxxxxxxxxx> 08.05.08 14:11 >>>
>The approach looks plausible. I think in its current form it will leave
>zombie L2/L3 pages hanging around and the domain will never actually
>properly die (e.g., still will be visible with the 'q' key). Because
>although you do get around to doing free_lX_table(), the type count and ref
>count of the L2/L3 pages will not drop to zero because the dead L3/L4 page
>never actually dropped its references properly.

Hmm, indeed, I should look for this after the next run.

>In actuality, since we know that we never have 'cross-domain' pagetable type
>references, we should actually be able to zap pagetable reference counts to
>zero. The only reason we don't do that right now is really because it
>provides good debugging info to see whether a domain's refcounts have got
>screwed up. But that would not prevent us doing something faster for NDEBUG
>builds, at least.
>
>Does that make sense?

Yes, except for me not immediately seeing why this is then not also a
problem for the current circular reference handling.

But really, rather than introducing (and fixing) the hack here I'd much
prefer a generic solution to the problem, and you didn't say a word on
the thoughts I had on that (but in a mail a couple of days ago you
indicated you might get around doing something in that area yourself,
so I half way implied you may have a mechanism in mind already).

Jan


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