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

    * Andi Kleen <ak@suse.de> wrote:

    > I still don't really think it will make much difference if the file
    > cache is local or global. Compare to disk IO it is still infinitely
    > faster, so a relatively small slowdown from going off node is not that
    > big an issue.

    well, maybe the SGI folks can give us some numbers?

    > > another thing: on NUMA, are the pagecache portions of readonly files
    > > (such as /usr binaries, etc.) duplicated across nodes in current
    > > kernels, or is it still random which node gets it?
    >
    > Random.
    >
    > > This too could be an
    > > EA caching attribute: whether to create per-node caches for file
    > > content.
    >
    > There were (ugly) patches floating around for text duplication, but
    > iirc the benchmarkers were still trying to figure out if it's even a
    > good idea. My guess it is not because CPUs tend to have very
    > aggressive prefetching for code streams which can deal with latency
    > well.

    you are a bit biased towards low-latency NUMA setups i guess (read:
    Opterons) :-) Obviously with a low NUMA factor, we dont have to deal
    with memory access assymetries all that much.

    But i think we should expand our file caching architecture into those
    caching details nevertheless: it's directly applicable to software
    driven clusters as well. There pagecache replication on nodes is a must,
    and obviously there it makes a big difference whether files are cached
    locally or remotely.

    Ingo
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