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Date: Wed, 24 Nov 2010 21:46:41 +0800
From: Wu Fengguang <fengguang.wu@intel.com>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andrew Morton <akpm@linux-foundation.org>, Jan Kara <jack@suse.cz>,
        "Li, Shaohua" <shaohua.li@intel.com>, Christoph Hellwig <hch@lst.de>,
        Dave Chinner <david@fromorbit.com>, "Theodore Ts'o" <tytso@mit.edu>,
        Chris Mason <chris.mason@oracle.com>, Mel Gorman <mel@csn.ul.ie>,
        Rik van Riel <riel@redhat.com>,
        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        linux-mm <linux-mm@kvack.org>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 06/13] writeback: bdi write bandwidth estimation
Message-ID: <20101124134641.GA12987@localhost>
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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]..