Re: [RFC 1/3] Framework for accurate node based statistics

[Nick Piggin]

Christoph Lameter wrote:
> [RFC] Framework for accurate node based statistics
>
> Currently we have various vm counters that are split per cpu. This arrangement
> does not allow access to per node statistics that are important to optimize
> VM behavior for NUMA architectures. All one can say from the per_cpu
> differential variables is how much a certain variable was changed by this cpu
> without being able to deduce how many pages in each node are of a certain type.
>
> This patch introduces a generic framework to allow accurate per node vm
> statistics through a large per node and per cpu array. The numbers are
> consolidated when the slab drainer runs (every 3 seconds or so) into global
> and per node counters. VM functions can then check these statistics by
> simply accessing the node specific or global counter.
>
> A significant problem with this approach is that the statistics are only
> accumulated every 3 seconds or so. I have tried various other approaches
> but they typically end up with having to add atomic variables to critical
> VM paths. I'd be glad if someone else had a bright idea on how to improve
> the situation.

Why not have per-node * per-cpu counters?

Or even use the current per-zone * per-cpu counters, and work out your
node details from there?

--
SUSE Labs, Novell Inc.

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