Re: [Xen-devel] [RFC v2][PATCH 1/3] docs: design and intended usage for NUMA-aware ballooning

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

>From: Jan Beulich [jbeulich@xxxxxxxx]
>
>Yes, supporting both modes is certainly desirable; I merely tried to
>point out that the description went too far in the direction of advocating
>only the enforce-a-node model (almost like this was the only sensible
>one from the NUMA perspective). Penalizing another guest should
>clearly not be a default action, but it may validly be a choice by the
>administrator.
>
>Jan
>
Ok, cool to know, and the point you're trying to make is a really valuable
one, and I agree with it. :-)

So, Yechen, in case you're up for another version of this series, here's
what I would recommend you to think about:

* take this design document and reorganize it a bit, in order to
  separate the generic description of the NUMA-aware ballooning
  concept, functioning, interface, etc., and the detail of the Linux
  implementation. I think those details could still live here
  (especially at this stage), but they should be in their own
  separate section(s), as an "example implementation"

* Given the issues/doubts about the new interface, could we
  have a first version of the code _without_ the new xenstore
  key that just does something as follows:
  - the user asks to balloon up/down by N pages
  - if the guest is a virtual NUMA enabled guest with Y
    virtual nodes, the ballooning driver gives/takes to/from
    him N/Y pages per each node.

Of course, when looking/implementing the latter point, do
not throw this code here away (I'm talking about the version
you submitted, with the new xenstore key)... Or at least,
I think it is a valuable addition, so if I were you, I wouldn't
throw it away.

I think it would be entirely possible to reach consensus on
the "evenly spreading without new xenstore key" version, as
a first step and upstream it. Afterwards, we will enhance the
interface (if we decide we like it) with the per-node targets.

What do you think?

I'm of course up for helping you with that, bot not before a couple
of weeks. :-P

Thanks and Regard,
Dario

--
<<This happens because I choose it to happen!>> (Raistlin Majere)
----------------------------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)
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