Re: [RFC] another way to speed up fake numa node page_alloc

[Paul Jackson <pj@sgi.com>]

I don't think you didn't answer my question.

I am suggesting we leave it enabled, and I said why.

You are suggesting we disable it unless numa nodes are being emulated.

  Why?  What benefit is there to disabling it at runtime?

And, no, I can't provide data.  It depends on how the system is setup
and used.

If someone has a system with many nodes (say 64, such as in your fake
numa tests) and a cpuset configuration and workload that loads many of
those nodes, forcing long zonelist scans, they will hit it just like
your tests did.

The real question is how common such systems, configurations and
workloads really are.

No amount of micro-benchmarking can answer that question.

Micro-benchmarks are of limited use in making design choices, except
when they are validated against real world workloads.

And as to why my position changed as to whether the zonelist scans
were ever a performance issue on real numa, I've already answered that
question ... a couple of times.  Let me know if you need me to repeat
this answer a third time.

-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@sgi.com> 1.925.600.0401

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