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

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Date:	Thu, 24 May 2012 11:15:47 +0200
From:	Jerome Marchand <jmarchan@...hat.com>
To:	Satoru Moriya <satoru.moriya@....com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	"lwoodman@...hat.com" <lwoodman@...hat.com>,
	"jweiner@...hat.com" <jweiner@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Richard Davies <richard.davies@...stichosts.com>,
	Seiji Aguchi <seiji.aguchi@....com>,
	"dle-develop@...ts.sourceforge.net" 
	<dle-develop@...ts.sourceforge.net>,
	Minchan Kim <minchan@...nel.org>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH RESEND] avoid swapping out with swappiness==0

On 05/23/2012 10:41 PM, Satoru Moriya wrote:
> Hi Andrew,
> 
> This patch has been reviewed for couple of months.
> 
> This patch *only* improves the behavior when the kernel has
> enough filebacked pages. It means that it does not change
> the behavior when kernel has small number of filebacked pages.
> 
> Kosaki-san pointed out that the threshold which we use
> to decide whether filebacked page is enough or not is not
> appropriate(*).
> 
> (*) http://www.spinics.net/lists/linux-mm/msg32380.html
> 
> As I described in (**), I believe that threshold discussion
> should be done in other thread because it affects not only
> swappiness=0 case and the kernel behave the same way with
> or without this patch below the threshold.
> 
> (**) http://www.spinics.net/lists/linux-mm/msg34317.html
> 
> The patch may not be perfect but, at least, we can improve
> the kernel behavior in the enough filebacked memory case
> with this patch. I believe it's better than nothing.
> 
> Do you have any comments about it?
> 
> NOTE: I updated the patch with Acked-by tags
> 
> ---
> Sometimes we'd like to avoid swapping out anonymous memory
> in particular, avoid swapping out pages of important process or
> process groups while there is a reasonable amount of pagecache
> on RAM so that we can satisfy our customers' requirements.
> 
> OTOH, we can control how aggressive the kernel will swap memory pages
> with /proc/sys/vm/swappiness for global and
> /sys/fs/cgroup/memory/memory.swappiness for each memcg.
> 
> But with current reclaim implementation, the kernel may swap out
> even if we set swappiness==0 and there is pagecache on RAM.
> 
> This patch changes the behavior with swappiness==0. If we set
> swappiness==0, the kernel does not swap out completely
> (for global reclaim until the amount of free pages and filebacked
> pages in a zone has been reduced to something very very small
> (nr_free + nr_filebacked < high watermark)).
> 
> Any comments are welcome.
> 
> Regards,
> Satoru Moriya
> 
> Signed-off-by: Satoru Moriya <satoru.moriya@....com>
> Acked-by: Minchan Kim <minchan@...nel.org>
> Acked-by: Rik van Riel <riel@...hat.com>
> 

Acked-by: Jerome Marchand <jmarchan@...hat.com>


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