linux-kernel - Re: [PATCH 03/19] mm: compaction: Add scanned and isolated counters for compaction

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Date:	Tue, 06 Nov 2012 12:35:20 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 03/19] mm: compaction: Add scanned and isolated counters
 for compaction

On 11/06/2012 04:14 AM, Mel Gorman wrote:
> Compaction already has tracepoints to count scanned and isolated pages
> but it requires that ftrace be enabled and if that information has to be
> written to disk then it can be disruptive. This patch adds vmstat counters
> for compaction called compact_migrate_scanned, compact_free_scanned and
> compact_isolated.
>
> With these counters, it is possible to define a basic cost model for
> compaction. This approximates of how much work compaction is doing and can
> be compared that with an oprofile showing TLB misses and see if the cost of
> compaction is being offset by THP for example. Minimally a compaction patch
> can be evaluated in terms of whether it increases or decreases cost. The
> basic cost model looks like this


> Signed-off-by: Mel Gorman <mgorman@...e.de>

Reviewed-by: Rik van Riel <riel@...hat.com>


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