Re: [patch 3/9] mempool - Make mempools NUMA aware

[Paul Jackson <pj@sgi.com>]

Matthew wrote:
> I'm glad we're on the same page now. :)  And yes, adding four "duplicate"
> *_mempool allocators was not my first choice, but I couldn't easily see a
> better way.

I hope the following comments aren't too far off target.

I too am inclined to prefer the __GFP_CRITICAL approach over this.
That or Andrea's suggestion, which except for a free hook, was entirely
outside of the page_alloc.c code paths.  Or Alan's suggested revival
of the old code to drop non-critical network patches in duress.

I am tempted to think you've taken an approach that raised some
substantial looking issues:

 * how to tell the system when to use the emergency pool
 * this doesn't really solve the problem (network can still starve)
 * it wastes memory most of the time
 * it doesn't really improve on GFP_ATOMIC

and just added another substantial looking issue:

 * it entwines another thread of complexity and performance costs
   into the important memory allocation code path.

Progress in the wrong direction ;).

> With large machines, especially as
> those large machines' workloads are more and more likely to be partitioned
> with something like cpusets, you want to be able to specify where you want
> your reserve pool to come from.

Cpusets is about performance, not correctness.  Anytime I get cornered
in the cpuset code, I prefer violating the cpuset containment, over
serious system failure.

-- 
                  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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