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

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Date:	Mon, 2 Apr 2012 10:10:12 -0700
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Satoru Moriya <satoru.moriya@....com>
Cc:	"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

2012/3/30 Satoru Moriya <satoru.moriya@....com>:
> Hello Kosaki-san,
>
> On 03/07/2012 01:18 PM, Satoru Moriya wrote:
>> On 03/07/2012 12:19 PM, KOSAKI Motohiro wrote:
>>> Thank you. I brought back to memory it. Unfortunately DB folks are
>>> still mainly using RHEL5 generation distros. At that time,
>>> swapiness=0 doesn't mean disabling swap.
>>>
>>> They want, "don't swap as far as kernel has any file cache page". but
>>> linux don't have such feature. then they used swappiness for emulate
>>> it. So, I think this patch clearly make userland harm. Because of, we
>>> don't have an alternative way.
>
> As I wrote in the previous mail(see below), with this patch
> the kernel begins to swap out when the sum of free pages and
> filebacked pages reduces less than watermark_high.
>
> 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?
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