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[Xen-devel] Re: non-zero order allocations in shadow code may prevent li

To: "Tim Deegan" <Tim.Deegan@xxxxxxxxxxxxx>
Subject: [Xen-devel] Re: non-zero order allocations in shadow code may prevent live migration
From: "Jan Beulich" <jbeulich@xxxxxxxxxx>
Date: Thu, 27 Sep 2007 12:28:10 +0100
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>>> Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx> 27.09.07 12:50 >>>
>At 10:51 +0100 on 27 Sep (1190890315), Jan Beulich wrote:
>> So the bottom line is - sh_set_allocation() really shouldn't need to allocate
>> non-zero order pages except for hvm domains.
>Actually, if you're having fragmentation issues, won't that stop you
>from booting HVM domains as well?

I'm sure we would, but in the given case the customer just cares about PV.

However, HVM would likely see the issue much less frequently if (as I assume,
but didn't verify) shadow mode gets enabled before normal domain memory
gets allocated, because that would generally allow a much wider pool for
picking out the needed higher order pages. Nevertheless I would think that
even for HVM domains the shadow shouldn't need to make its entire
allocation in order 2 chunks, but could limit this to just the amount it really
knows it'll need (1 per vCPU as I understand it), then continue with order 1
chunks (not sure about their count, but for forward progress I think you'll
need at most 6 {,f}l1_32_shadow pages per vCPU).


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