linux-kernel - Re: [PATCH 3/5] writeback: dirty rate control

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Message-ID: <1312996226.23660.43.camel@twins>
Date:	Wed, 10 Aug 2011 19:10:26 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Vivek Goyal <vgoyal@...hat.com>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@....de>,
	Dave Chinner <david@...morbit.com>,
	Greg Thelen <gthelen@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Andrea Righi <arighi@...eler.com>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/5] writeback: dirty rate control

On Wed, 2011-08-10 at 22:00 +0800, Wu Fengguang wrote:
> 
> > Although I'm not quite sure how he keeps fairness in light of the
> > sleep time bounding to MAX_PAUSE.
> 
> Firstly, MAX_PAUSE will only be applied when the dirty pages rush
> high (dirty exceeded).  Secondly, the dirty exceeded state is global
> to all tasks, in which case each task will sleep for MAX_PAUSE equally.
> So the fairness is still maintained in dirty exceeded state. 

Its not immediately apparent how dirty_exceeded and MAX_PAUSE interact,
but having everybody sleep MAX_PAUSE doesn't necessarily mean its fair,
its only fair if they dirty at the same rate.
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