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Subject: Re: [PATCH 03/13] writeback: per-task rate limit on
 balance_dirty_pages()
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Wu Fengguang <fengguang.wu@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, Jan Kara <jack@suse.cz>,
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Date: Wed, 24 Nov 2010 11:49:28 +0100
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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.