From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [PATCH 03/13] writeback: per-task rate limit on
 balance_dirty_pages()
Date: Wed, 24 Nov 2010 11:49:28 +0100
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References: <20101117042720.033773013@intel.com>
	 <20101117042849.650810571@intel.com> <1290594187.2072.440.camel@laptop>
	 <20101124104331.GA6096@localhost>
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Cc: Andrew Morton <akpm@linux-foundation.org>, Jan Kara <jack@suse.cz>,
	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>
To: Wu Fengguang <fengguang.wu@intel.com>
Return-path: <linux-kernel-owner@vger.kernel.org>
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On Wed, 2010-11-24 at 18:43 +0800, Wu Fengguang wrote:
> On Wed, Nov 24, 2010 at 06:23:07PM +0800, Peter Zijlstra wrote:
> > On Wed, 2010-11-17 at 12:27 +0800, Wu Fengguang wrote:
> > > +       if (unlikely(current->nr_dirtied >= current->nr_dirtied_pause ||
> > > +                    bdi->dirty_exceeded)) {
> > > +               balance_dirty_pages(mapping, current->nr_dirtied);
> > > +               current->nr_dirtied = 0;
> > >         } 
> > 
> > Was it a conscious choice to use
> >   current->nr_dirtied = 0
> > over 
> >   current->nr_dirtied -= current->nr_dirtied_pause
> > ?
> > 
> > The former will cause a drift in pause times due to truncation of the
> > excess.
> 
> It should be fine in either way, as long as the "truncated" number is
> passed to balance_dirty_pages():
> 
> +               balance_dirty_pages(mapping, current->nr_dirtied);
> +               current->nr_dirtied = 0;
> 
> or
> 
> +               balance_dirty_pages(mapping, current->nr_dirtied_pause);
> +               current->nr_dirtied -= current->nr_dirtied_pause;

ok, just wanted to make sure you'd considered it.