linux-kernel - Re: [PATCH 03/10] writeback: stop background writeback when below background threshold

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Date:	Fri, 25 Sep 2009 08:47:07 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Jens Axboe <jens.axboe@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Li, Shaohua" <shaohua.li@...el.com>,
	"chris.mason@...cle.com" <chris.mason@...cle.com>,
	"jack@...e.cz" <jack@...e.cz>
Subject: Re: [PATCH 03/10] writeback: stop background writeback when below
	background threshold

On Fri, Sep 25, 2009 at 12:26:00AM +0800, Peter Zijlstra wrote:
> On Thu, 2009-09-24 at 18:13 +0200, Jens Axboe wrote:
> 
> > > > >  	for (;;) {
> > > > >  		/*
> > > > > +		 * Stop writeback when nr_pages has been consumed
> > > > >  		 */
> > > > > +		if (args->nr_pages <= 0)
> > > > >  			break;
> > > > >  
> > > > >  		/*
> > > > > +		 * For background writeout, stop when we are below the
> > > > > +		 * background dirty threshold
> > > > >  		 */
> > > > > +		if (args->for_background && !over_bground_thresh())
> > > > >  			break;
> > > > 
> > > > 
> > > > What I'm not getting is why this is conditional on for_background(),
> > > > shouldn't we always stop writeback when below the background threshold?
> > > 
> > > Ah, that would be for things like sync, which need to write out
> > > everything, right?

Besides sync, it's reasonable for periodic writeback to write all
inodes as long as they are expired.

> > Yes, wb_writeback() handles any kind of writeback. The definition of our
> > background writeout is to stop when we are no longer over the background
> > writeout threshold.
> 
> Right, ok
> 
> Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>

Thanks! This patch was partly inspired by your comments :)

Regards,
Fengguang
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