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

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Date:	Mon, 22 Apr 2013 08:54:24 +0200
From:	Zlatko Calusic <zcalusic@...sync.net>
To:	Simon Jeons <simon.jeons@...il.com>
CC:	Mel Gorman <mgorman@...e.de>,
	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 22.04.2013 08:43, Simon Jeons wrote:
> Hi Zlatko,
> On 04/22/2013 02:37 PM, Zlatko Calusic wrote:
>> On 12.04.2013 22:07, 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]
>>>
>>> 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).
>>>
>>
>> JFTR, v3 kswapd uses about 15% more CPU time than v2. 2:50 kswapd CPU
>> time after 6 days 14h uptime.
>>
>> And find attached another debugging graph that shows how ANON pages
>> are privileged in the ZONE_NORMAL on a 4GB machine. Take notice that
>> the number of pages in the ZONE_DMA32 is scaled (/5) to fit the graph
>> nicely.
>>
>
> Could you tell me how you draw this picture?
>

It's a home made server monitoring system. I just added the code needed 
to graph the size of active + inactive LRU lists, per zone and per type. 
Check out http://oss.oetiker.ch/rrdtool/

-- 
Zlatko

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