linux-kernel - Re: [PATCH 08/13] writeback: quit throttling when bdi dirty pages dropped low

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Message-ID: <1290602811.2072.462.camel@laptop>
Date:	Wed, 24 Nov 2010 13:46:51 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, Jan Kara <jack@...e.cz>,
	Christoph Hellwig <hch@....de>,
	Dave Chinner <david@...morbit.com>,
	Theodore Ts'o <tytso@....edu>,
	Chris Mason <chris.mason@...cle.com>,
	Mel Gorman <mel@....ul.ie>, Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-mm <linux-mm@...ck.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 08/13] writeback: quit throttling when bdi dirty pages
 dropped low

On Wed, 2010-11-24 at 20:30 +0800, Wu Fengguang wrote:
> 
> For the 1-dd case, it looks better to lower the break threshold to
> 125ms. After all, it's not easy for the dirty pages to drop by 250ms
> worth of data when you only slept 200ms (note: the max pause time has
> been doubled mainly for servers).
> 
> -               if (nr_dirty < dirty_thresh &&
> -                   bdi_prev_dirty - bdi_dirty > (long)bdi->write_bandwidth / 4)
> +               if (nr_dirty <= dirty_thresh &&
> +                   bdi_prev_dirty - bdi_dirty > (long)bdi->write_bandwidth / 8)
>                         break;

Hrm, but 125ms worth in 200ms is rather easy, you'd want to keep that
limit above what the pause should give you, right?

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