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

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 14/5/08 16:54, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

> I'm afraid that's not the case - after they are now using the domain
> shutdown fix successfully, they upgraded the machine to 64G and
> the system fails to boot. Sounds exactly like other reports we had on
> the list regarding boot failures with lots of memory that can be avoided
> using dom0_mem=<much smaller value>. As I understand it, this is
> due to the way the kernel creates its 1:1 mapping - the hypervisor has
> to validate the whole tree from each L4 entry being installed in a single
> step - for a 4G machine I measured half a second for this operation, so
> obviously anything beyond 32G is open for problems when the PM timer
> is in use.

Hmm, yes that makes sense. 32GB is 8M ptes, so I could imagine that taking a
while to validate. Anyhow this obviously needs fixing regardless of the
specific details of this specific failure case.

> Unless you tell me that this is on your very short term agenda to work on,
> I'll make an attempt at finding a reasonable solution starting tomorrow.

Yes, I'll sort this one out hopefully by next week. I think this can be
solved pretty straightforwardly. It's the encoding of the continuation into
the page_info structure, and synchronisation of that, that needs some
back-of-envelope thought. As long as there are not too many callers of
{get,put}_page_type(L{2,3,4}_pagetable), and I don't think we have that
many, then the changes should be pretty localised. Only those callers have
to deal with 'EAGAIN' (or equivalent).

 -- Keir



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