linux-kernel - Re: [PATCH] mm: wait for congestion to clear on all zones

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Message-Id: <20130109134816.db51a820.akpm@linux-foundation.org>
Date:	Wed, 9 Jan 2013 13:48:16 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Zlatko Calusic <zlatko.calusic@...on.hr>
Cc:	Mel Gorman <mgorman@...e.de>, Hugh Dickins <hughd@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	linux-mm <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: wait for congestion to clear on all zones

On Wed, 09 Jan 2013 22:41:48 +0100
Zlatko Calusic <zlatko.calusic@...on.hr> wrote:

> Currently we take a short nap (HZ/10) and wait for congestion to clear
> before taking another pass with lower priority in balance_pgdat(). But
> we do that only for the highest zone that we encounter is unbalanced
> and congested.
> 
> This patch changes that to wait on all congested zones in a single
> pass in the hope that it will save us some scanning that way. Also we
> take a nap as soon as congested zone is encountered and sc.priority <
> DEF_PRIORITY - 2 (aka kswapd in trouble).
> 
> ...
>
> The patch is against the mm tree. Make sure that
> mm-avoid-calling-pgdat_balanced-needlessly.patch is applied first (not
> yet in the mmotm tree). Tested on half a dozen systems with different
> workloads for the last few days, working really well!

But what are the user-observable effcets of this change?  Less kernel
CPU consumption, presumably?  Did you quantify it?

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