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Message-Id: <20110818165428.4f01a1b9.akpm@linux-foundation.org>
Date:	Thu, 18 Aug 2011 16:54:28 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
	XFS <xfs@....sgi.com>, Dave Chinner <david@...morbit.com>,
	Christoph Hellwig <hch@...radead.org>,
	Johannes Weiner <jweiner@...hat.com>,
	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Rik van Riel <riel@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>
Subject: Re: [PATCH 6/7] mm: vmscan: Throttle reclaim if encountering too
 many dirty pages under writeback

On Wed, 10 Aug 2011 11:47:19 +0100
Mel Gorman <mgorman@...e.de> wrote:

> The percentage that must be in writeback depends on the priority. At
> default priority, all of them must be dirty. At DEF_PRIORITY-1, 50%
> of them must be, DEF_PRIORITY-2, 25% etc. i.e. as pressure increases
> the greater the likelihood the process will get throttled to allow
> the flusher threads to make some progress.

It'd be nice if the code comment were to capture this piece of implicit
arithmetic.  After all, it's a magic number and magic numbers should
stick out like sore thumbs.

And.. how do we know that the chosen magic numbers were optimal?
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