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

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Date:	Wed, 09 Jan 2013 23:52:47 +0100
From:	Zlatko Calusic <zlatko.calusic@...on.hr>
To:	Andrew Morton <akpm@...ux-foundation.org>
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 09.01.2013 22:48, Andrew Morton wrote:
> 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?
>

And I forgot to answer all the questions... :(

Actually, I did record kswapd CPU usage after 5 days of uptime and I 
intend to compare it with the new data (after few more days pass). I 
expect maybe slightly better results.

But, I think it's obvious from my first reply that my primary goal with 
this patch is correctness, not optimization. So, I won't be dissapointed 
a little bit if kswapd CPU usage stays the same, so long as the memory 
utilization remains this smooth. ;)

-- 
Zlatko
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