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

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Date:	Tue, 09 Aug 2011 18:16:30 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Wu Fengguang <fengguang.wu@...el.com>,
	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 Tue, 2011-08-09 at 11:50 -0400, Vivek Goyal wrote:
> 
> So IIUC, bdi->dirty_ratelimit is the dynmically adjusted desired rate
> limit (based on postion ratio, dirty_bw and write_bw). But this seems
> to be overall bdi limit and does not seem to take into account the
> number of tasks doing IO to that bdi (as your comment suggests). So
> it probably will track write_bw as opposed to write_bw/N. What am
> I missing? 

I think the per task thing comes from him using the pages_dirtied
argument to balance_dirty_pages() to compute the sleep time. Although
I'm not quite sure how he keeps fairness in light of the sleep time
bounding to MAX_PAUSE.


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