Re: [PATCH 00/23] per device dirty throttling -v10

From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: John Stoffel <john@stoffel.org>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	miklos@szeredi.hu, akpm@linux-foundation.org, neilb@suse.de,
	dgc@sgi.com, tomoki.sekiyama.qu@hitachi.com,
	nikita@clusterfs.com, trond.myklebust@fys.uio.no,
	yingchao.zhou@gmail.com, richard@rsk.demon.co.uk,
	torvalds@linux-foundation.org
Subject: Re: [PATCH 00/23] per device dirty throttling -v10
Date: Wed, 12 Sep 2007 11:00:59 +0200	[thread overview]
Message-ID: <1189587659.21778.104.camel@twins> (raw)
In-Reply-To: <18151.20356.862163.430265@stoffel.org>

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On Tue, 2007-09-11 at 22:31 -0400, John Stoffel wrote:

I hope the snipped questions were sufficiently answered in the other
mail. If not, holler :-)

> Peter> 3 is done by also scaling the dirty limit proportional to the
> Peter> current task's recent dirty rate.
> 
> Do you mean task or device here?  I'm just wondering how well this
> works with a bunch of devices with wildly varying speeds.  

Task. What I do is modify the limit like this:

  current_limit = dirty_limit * p(bdi_writeout) * (1 - p(task_dirty)/8)

Where the p() values are [0, 1].

By including the inverse of the task dirty rate one gets that tasks that
are more agressive dirtiers get throttled more aggressively, whereas
tasks that occasionally dirty a page get a little more room.

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