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    SubjectRe: [PATCH 1/5] cpuset memory spread basic implementation

    * Andi Kleen <> wrote:

    > On Tuesday 07 February 2006 13:30, Ingo Molnar wrote:
    > > you are a bit biased towards low-latency NUMA setups i guess (read:
    > > Opterons) :-)
    > Well they are the vast majority of NUMA systems Linux runs on.
    > And there are more than just Opterons, e.g. IBM Summit. And even the
    > majority of Altixes are not _that_ big.
    > Of course we need to deal somehow with the big systems, but for the
    > good defaults the smaller systems are more important.

    i'm not sure i understand your point. You said that for small systems
    with a low NUMA factor it doesnt really matter where the pagecache is
    placed. I mostly agree with that. And since placement makes no
    difference there, we can freely shape things for the systems where it
    does make a difference. It will probably make a small win on smaller
    systems too, as a bonus. Ok?

    > Big systems tend to have capable administrators who are willing to
    > tweak them. But that's rarely the case with the small systems. So I
    > think as long as the big system can be somehow made to work with
    > special configuration and ignoring corner cases that's fine. But for
    > the low NUMA systems it should perform as well as possibly out of the
    > box.

    i also mentioned software-based clusters in the previous mail, so it's
    not only about big systems. Caching attributes are very much relevant
    there. Tightly integrated clusters can be considered NUMA systems with a
    NUMA factor of 1000 or so (or worse).

    > > Obviously with a low NUMA factor, we dont have to deal
    > > with memory access assymetries all that much.
    > That is why I proposed "nearby policy". It can turn a system with a
    > large NUMA factor into a system with a small NUMA factor.

    well, would the "nearby policy" make a difference on the small systems?
    Small systems (to me) are just a flat and symmetric hierarchy of nodes -
    the next step from SMP. So there's really just two distances: local to
    the node, and one level of 'alien'. Or do you include systems in this
    category that have bigger assymetries?

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