Re: [PATCH 1/2] mm: page allocator: Adjust the per-cpu counterthreshold when memory is low

[Christoph Lameter]

On Fri, 29 Oct 2010, Andrew Morton wrote:

> > Doing that caused cache misses in the past and reduced the performance of
> > the ZVCs. This way the threshold is in the same cacheline as the
> > differentials.
>
> This sounds wrong.  As long as that threshold isn't stored in a
> cacheline which other CPUs are modifying, all CPUs should be able to
> happily cache it.  Maybe it needed a bit of padding inside the zone
> struct.

High speed cpu caches are a very scarce resource. The differentials are
not in the zone struct. Tried to put it onto a single cacheline. Even that
did not do the trick for the large configurations.

The same optimizations are done in the slab allocators by the way.

Use of the percpu_counter() would at least quadruple the cache footprint
in use for the counters. percpu_counters() is using s32 and not s8.

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