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Re: [Xen-devel] [Hackathon minutes] PV frontends/backends and NUMA machines

On 21/05/13 14:43, Dario Faggioli wrote:
On mar, 2013-05-21 at 12:47 +0100, Jan Beulich wrote:
On 21.05.13 at 12:58, Dario Faggioli <raistlin@xxxxxxxx> wrote:
Well, sure, but then, again, how do you control which (and not only how
much) memory is taken from which node?
Hmm, I may not have followed, but why is "which" important here at
all? The only (usual) restriction should apply regarding preservation of
memory below 4G.

It is if you want Dom0 to think it is running, say, on 2 nodes and
actually have the memory, say, in the range 0-1G accessed quicker from
d0v0 (vcpu0 of Dom0), and the vice versa with memory within 1-2G and

That enables NUMA optimization _inside_ Dom0, like the pinning of the
backends and all the other stuff discussed (during the Hackathon and) in
this thread.

However, to do that, we, I think, need to be able not only to specify
that we want 1G worth of memory on one specific node, but also to
request explicitly for some of Dom0's PFN to be here and for some others
to be there, as we were saying earlier in the thread with Tim.

One thing that I wanted to add to this discussion -- unless there's some way for the toolstack to figure out, for each node, how much memory is currently free *and* how much memory could be freed by dom0 on that node, and a way to ask dom0 to free memory from a specific a node, then booting with dom0 having all the memory is basically going to make all of our NUMA work a noop.

We may end up having to switch from defaulting to giving dom0 and autoballooning to giving dom0 a fixed amount.


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