Re: [PATCH]: Free pages from local pcp lists under tight memoryconditions

From: Paul Jackson
Date: Wed Nov 23 2005 - 22:09:07 EST

Rohit wrote:
> I thought Nick came up with some of the constant values like batch
> size to tackle the page coloring issue specifically.

I think this came about on a linux-ia64 thread started by Jack Steiner:
Subject: per_cpu_pagesets degrades MPI performance
From: Jack Steiner <>
Date: 2005-04-05 05:28:27

Jack reported that per_cpu_pagesets were degrading some MPI benchmarks due
to adverse page coloring. Nick responded, recommending a non-power of two
batch size. Jack found that this helped nicely. This thread trails off,
but seems to be the origins of the 2**n-1 batch size in:

* Clamp the batch to a 2^n - 1 value. Having a power ...
batch = (1 << fls(batch + batch/2)) - 1;

I don't see here evidence that "per_cpu_pagelist is ... one single main
reason the coloring effect is drastically reduced in 2.6 (over 2.4)
based kernels." Rather in this case anyway a batch size not a power of
two was apparently needed to keep per_cpu_pagesets from hurting
performance due to page coloring affects on some workloads.

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