Re: [TAKE] memory page_alloc zonelist caching speedup

[Paul Jackson <pj@sgi.com>]

Andi wrote:
> I think some more precise numbers would be appreciated before doing
> such changes.

Aren't there more precise numbers further down in the message to which
you were responding?

> Yes but you will add latencies for cache line bounces won't you?
> The old zone lists were completely read only. That is what worries me 
> most.

There is one zonelist_cache per node, added at the end of the regular
zonelist array for each node.  It will have a few words updated
typically at the rate of once per second by the CPUs sharing that node.

>From what my tests showed, and from what I'd expect, updating a few
node local words per second is not a problem.

If you have a particular architecture in mind for which the tradeoffs
in the proposed patch don't seem right, could you spell out that
architecture a bit, so we can sensibly consider whether some
refinements to this patch will suit that architecture better?

Certainly, from the numbers that I have, and by private email that
Rohit Seth has on a different architecture, this patch is neutral or a
win for the cases we considered, depending on the degree of node
locality of the memory accesses.

-- 
                  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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