linux-kernel - RE: [RFC][PATCH] avoid swapping out with swappiness==0

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Date:	Fri, 20 Apr 2012 20:21:28 -0400
From:	Satoru Moriya <satoru.moriya@....com>
To:	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Jerome Marchand <jmarchan@...hat.com>
CC:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	"jweiner@...hat.com" <jweiner@...hat.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"riel@...hat.com" <riel@...hat.com>,
	"lwoodman@...hat.com" <lwoodman@...hat.com>,
	"shaohua.li@...el.com" <shaohua.li@...el.com>,
	"dle-develop@...ts.sourceforge.net" 
	<dle-develop@...ts.sourceforge.net>,
	Seiji Aguchi <seiji.aguchi@....com>
Subject: RE: [RFC][PATCH] avoid swapping out with swappiness==0

Hi,

Sorry for my late reply.

On 04/04/2012 01:38 PM, KOSAKI Motohiro wrote:
> (4/3/12 4:25 AM), Jerome Marchand wrote:
>> On 04/02/2012 07:10 PM, KOSAKI Motohiro wrote:
>>> 2012/3/30 Satoru Moriya<satoru.moriya@....com>:
>>>> So the kernel reclaims pages like following.
>>>>
>>>> nr_free + nr_filebacked>= watermark_high: reclaim only filebacked pages
>>>> nr_free + nr_filebacked<   watermark_high: reclaim only anonymous pages
>>>
>>> How?
>>
>> get_scan_count() checks that case explicitly:
>>
>>     if (global_reclaim(sc)) {
>>         free  = zone_page_state(mz->zone, NR_FREE_PAGES);
>>         /* If we have very few page cache pages,
>>            force-scan anon pages. */
>>         if (unlikely(file + free<= high_wmark_pages(mz->zone))) {
>>             fraction[0] = 1;
>>             fraction[1] = 0;
>>             denominator = 1;
>>             goto out;
>>         }
>>     }
> 
> Eek. This is silly. Nowaday many people enabled THP and it increase zone watermark.
> so, high watermask is not good threshold anymore.

Ah yes, it is not so small now.
On 4GB server, without THP min_free_kbytes is 8113 but
with THP it is 67584.

How about using low watermark or min watermark?
Are they still big?

...or should we use other value? 

Regards,
Satoru
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