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Re: [PATCH 01/27] mm, vmstat: Add infrastructure for per-node vmstats

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  Re: [PATCH 01/27] mm, vmstat: Add infrastructure for per-node  vmstats Christoph Lameter <cl@linux.com> - 2016-06-13 19:30 +0200
    Re: [PATCH 01/27] mm, vmstat: Add infrastructure for per-node vmstats Mel Gorman <mgorman@techsingularity.net> - 2016-06-14 16:30 +0200

#1421069 — Re: [PATCH 01/27] mm, vmstat: Add infrastructure for per-node vmstats

On Thu, 9 Jun 2016, Mel Gorman wrote:

> VM statistic counters for reclaim decisions are zone-based. If the kernel
> is to reclaim on a per-node basis then we need to track per-node statistics
> but there is no infrastructure for that. The most notable change is that

There is node_page_state() so the value of any counter per node is already
available. Note that some of the counters (NUMA_xx) for example do not
make much sense as per zone counters and are effectively used as per node
counters.

So the main effect you are looking for is to have the counters stored in
the per node structure as opposed to the per zone struct in order to
avoid the summing? Doing so duplicates a large amount of code it seems.

If you do this then also move over certain counters that have more of a
per node use from per zone to per node. Like the NUMA_xxx counters.

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#1421936 — Re: [PATCH 01/27] mm, vmstat: Add infrastructure for per-node vmstats

On Mon, Jun 13, 2016 at 12:26:13PM -0500, Christoph Lameter wrote:
> On Thu, 9 Jun 2016, Mel Gorman wrote:
> 
> > VM statistic counters for reclaim decisions are zone-based. If the kernel
> > is to reclaim on a per-node basis then we need to track per-node statistics
> > but there is no infrastructure for that. The most notable change is that
> 
> There is node_page_state() so the value of any counter per node is already
> available. Note that some of the counters (NUMA_xx) for example do not
> make much sense as per zone counters and are effectively used as per node
> counters.
> 
> So the main effect you are looking for is to have the counters stored in
> the per node structure as opposed to the per zone struct in order to
> avoid the summing?

Yes.

> Doing so duplicates a large amount of code it seems.
> 

Also yes. I considered macro magic to cover it but it turned into a
major mess. They could always be summed so it would be a minor
performance dent and a heavier cache footprint.

> If you do this then also move over certain counters that have more of a
> per node use from per zone to per node. Like the NUMA_xxx counters.
> 

As the NUMA counters are consumed by userspace, I worried that it would
break some tools. If the rest of the series gets solidified then I will
do it as a single patch on top so it can be reverted if necessary
relatively easily.

-- 
Mel Gorman
SUSE Labs

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