* Andi Kleen <[email protected]> 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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