linux-kernel - Re: [PATCH] documentation: clarify dirty_ratio and dirty_background

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Message-Id: <20081009105157.dd47d109.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 9 Oct 2008 10:51:57 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	righi.andrea@...il.com
Cc:	Randy Dunlap <randy.dunlap@...cle.com>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michael Rubin <mrubin@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] documentation: clarify dirty_ratio and
 dirty_background_ratio description

On Wed, 08 Oct 2008 12:52:28 +0200
Andrea Righi <righi.andrea@...il.com> wrote:

> The current documentation of dirty_ratio and dirty_background_ratio is a
> bit misleading.
> 
> In the documentation we say that they are "a percentage of total system
> memory", but the current page writeback policy, intead, is to apply the
> percentages to the dirtyable memory, that means free pages + reclaimable
> pages.
> 
Right.

> Better to be more explicit to clarify this concept.
> 
> Signed-off-by: Andrea Righi <righi.andrea@...il.com>

But I wonder "reclaimable memory" seems to be a difficult word for users....

"free pages + mapped pages + file cache, not including locked page and HugePage"
?
Anyway,
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

> ---
>  Documentation/filesystems/proc.txt |   11 ++++++-----
>  1 files changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
> index f566ad9..be69c8b 100644
> --- a/Documentation/filesystems/proc.txt
> +++ b/Documentation/filesystems/proc.txt
> @@ -1380,15 +1380,16 @@ causes the kernel to prefer to reclaim dentries and inodes.
>  dirty_background_ratio
>  ----------------------
>  
> -Contains, as a percentage of total system memory, the number of pages at which
> -the pdflush background writeback daemon will start writing out dirty data.
> +Contains, as a percentage of the dirtyable system memory (free pages +
> +reclaimable pages), the number of pages at which the pdflush background
> +writeback daemon will start writing out dirty data.
>  
>  dirty_ratio
>  -----------------
>  
> -Contains, as a percentage of total system memory, the number of pages at which
> -a process which is generating disk writes will itself start writing out dirty
> -data.
> +Contains, as a percentage of the dirtyable system memory (free pages +
> +reclaimable pages), the number of pages at which a process which is generating
> +disk writes will itself start writing out dirty data.
>  
>  dirty_writeback_centisecs
>  -------------------------
> 

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