linux-kernel - Re: [PATCH -mm] mm: fine-grained dirty_ratio_pcm and dirty_background_ratio

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Message-Id: <20081110131255.ce71ce60.akpm@linux-foundation.org>
Date:	Mon, 10 Nov 2008 13:12:55 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	righi.andrea@...il.com
Cc:	kamezawa.hiroyu@...fujitsu.com, rientjes@...gle.com,
	balbir@...ux.vnet.ibm.com, mrubin@...gle.com, menage@...gle.com,
	dave@...ux.vnet.ibm.com, chlunde@...g.uio.no, dpshah@...gle.com,
	eric.rannaud@...il.com, fernando@....ntt.co.jp, agk@...rceware.org,
	m.innocenti@...eca.it, s-uchida@...jp.nec.com, ryov@...inux.co.jp,
	matt@...ehost.com, dradford@...ehost.com,
	kosaki.motohiro@...fujitsu.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, containers@...ts.osdl.org
Subject: Re: [PATCH -mm] mm: fine-grained dirty_ratio_pcm and
 dirty_background_ratio_pcm (v2)

On Mon, 10 Nov 2008 21:58:28 +0100
Andrea Righi <righi.andrea@...il.com> wrote:

> The current granularity of 5% of dirtyable memory for dirty pages writeback is
> too coarse for large memory machines and this will get worse as
> memory-size/disk-speed ratio continues to increase.
> 
> These large writebacks can be unpleasant for desktop or latency-sensitive
> environments, where the time to complete each writeback can be perceived as a
> lack of responsiveness by the whole system.
> 
> Following there's a similar solution as discussed in [1], but a little
> bit simplified in order to provide the same functionality (in particular
> to avoid backward compatibility problems) and reduce the amount of code
> needed to implement an in-kernel parser to handle percentages with
> decimals digits.
> 
> The kernel provides the following parameters:
>  - dirty_ratio, dirty_background_ratio in percentage (1 ... 100)
>  - dirty_ratio_pcm, dirty_background_ratio_pcm in units of percent mille (1 ... 100,000)

hm, so how long until dirty_ratio_pcm becomes too coarse...

What happened to the idea of specifying these in units of kilobytes?
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