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

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Date:	Wed, 12 Sep 2007 11:00:59 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	John Stoffel <john@...ffel.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	miklos@...redi.hu, akpm@...ux-foundation.org, neilb@...e.de,
	dgc@....com, tomoki.sekiyama.qu@...achi.com, nikita@...sterfs.com,
	trond.myklebust@....uio.no, yingchao.zhou@...il.com,
	richard@....demon.co.uk, torvalds@...ux-foundation.org
Subject: Re: [PATCH 00/23] per device dirty throttling -v10

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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