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

[Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>]

At 12:28 +0100 on 27 Sep (1190896090), Jan Beulich wrote:
> 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),

For correctness, yes.  At least 1 per process in the working set for
anything like reasonable performance.

> 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).

ISTR the number came out at something unpleasant like thirteen after all
the VAs you might need for a single x86 instruction were accounted for.
But then we realised that even a heavily pessimistic lower bound was so
far below the threshold of acceptable performance that it wasn't worth
being precise. :)

Tim.

-- 
Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>, XenSource UK Limited
Registered office c/o EC2Y 5EB, UK; company number 05334508

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