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

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Message-ID: <20160614142506.GA1868@techsingularity.net>
Date:	Tue, 14 Jun 2016 15:25:07 +0100
From:	Mel Gorman <mgorman@...hsingularity.net>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>, Rik van Riel <riel@...riel.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: 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