linux-kernel - Re: [PATCH 01/13] writeback: IO-less balance_dirty

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Date:	Wed, 17 Nov 2010 12:19:26 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Theodore Ts'o <tytso@....edu>,
	Chris Mason <chris.mason@...cle.com>,
	Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.cz>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Jens Axboe <axboe@...nel.dk>, Mel Gorman <mel@....ul.ie>,
	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Christoph Hellwig <hch@....de>, 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 01/13] writeback: IO-less balance_dirty_pages()

> BEHAVIOR CHANGE
> ===============
> 
> Users will notice that the applications will get throttled once the
> crossing the global (background + dirty)/2=15% threshold. For a single
> "cp", it could be soft throttled at 2*bdi->write_bandwidth around 15%

s/2/8/

Sorry, the initial soft throttle bandwidth for "cp" is about 8 times
of bdi bandwidth when reaching 15% dirty pages.

> dirty pages, and be balanced at speed bdi->write_bandwidth around 17.5%
> dirty pages. Before patch, the behavior is to just throttle it at 17.5%
> dirty pages.
> 
> Since the task will be soft throttled earlier than before, it may be
> perceived by end users as performance "slow down" if his application
> happens to dirty more than ~15% memory.
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