linux-kernel - Re: [PATCH 0/10] Reduce system disruption due to kswapd V2

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Message-ID: <20130412204129.GA13146@suse.de>
Date:	Fri, 12 Apr 2013 21:41:50 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Zlatko Calusic <zcalusic@...sync.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	dormando <dormando@...ia.net>,
	Satoru Moriya <satoru.moriya@....com>,
	Michal Hocko <mhocko@...e.cz>, Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/10] Reduce system disruption due to kswapd V2

On Fri, Apr 12, 2013 at 10:07:54PM +0200, Zlatko Calusic wrote:
> On 12.04.2013 21:40, Mel Gorman wrote:
> >On Thu, Apr 11, 2013 at 10:55:13PM +0200, Zlatko Calusic wrote:
> >>On 09.04.2013 13:06, Mel Gorman wrote:
> >><SNIP>
> >>
> >>- The only slightly negative thing I observed is that with the patch
> >>applied kswapd burns 10x - 20x more CPU. So instead of about 15
> >>seconds, it has now spent more than 4 minutes on one particular
> >>machine with a quite steady load (after about 12 days of uptime).
> >>Admittedly, that's still nothing too alarming, but...
> >>
> >
> >Would you happen to know what circumstances trigger the higher CPU
> >usage?
> >
> 
> Really nothing special. The server is lightly loaded, but it does
> enough reading from the disk so that pagecache is mostly populated
> and page reclaiming is active. So, kswapd is no doubt using CPU time
> gradually, nothing extraordinary.
> 
> When I sent my reply yesterday, the server uptime was 12 days, and
> kswapd had accumulated 4:28 CPU time. Now, approx 24 hours later (13
> days uptime):
> 
> root        23  0.0  0.0      0     0 ?        S    Mar30   4:52 [kswapd0]
> 

Ok, that's not too crazy.

> I will apply your v3 series soon and see if there's any improvement
> wrt CPU usage, although as I said I don't see that as a big issue.
> It's still only 0.013% of available CPU resources (dual core CPU).
> 

Excellent, thanks very much for testing and reporting back. I read your
mail on the zone balancing and FWIW I would not have expected this series
to have any impact on it. I do not have a good theory yet as to what the
problem is but I'll give it some thought and se what I come up with. I'll
be at LSF/MM next week so it might take me a while.

-- 
Mel Gorman
SUSE Labs
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