linux-kernel - Re: [PATCH 06/13] writeback: bdi write bandwidth estimation

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Message-ID: <20101124134641.GA12987@localhost>
Date:	Wed, 24 Nov 2010 21:46:41 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, Jan Kara <jack@...e.cz>,
	"Li, Shaohua" <shaohua.li@...el.com>,
	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 06/13] writeback: bdi write bandwidth estimation

On Wed, Nov 24, 2010 at 09:42:09PM +0800, Peter Zijlstra wrote:
> On Wed, 2010-11-24 at 21:20 +0800, Wu Fengguang wrote:
> > >         (jiffies - bdi->write_bandwidth_update_time < elapsed)
> > 
> > this will be true if someone else has _done_ overlapped estimation,
> > otherwise it will equal:
> > 
> >         jiffies - bdi->write_bandwidth_update_time == elapsed
> > 
> > Sorry the comment needs updating. 
> 
> Right, but its racy as hell..

Yeah, for N concurrent dirtiers, plus the background flusher, only
one is able to update write_bandwidth[_update_time]..

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