linux-kernel - Re: [patch 4/5] mm: writeback: throttle __GFP

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Message-ID: <20110804072745.GA31039@tiehlicka.suse.cz>
Date:	Thu, 4 Aug 2011 09:27:45 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Johannes Weiner <jweiner@...hat.com>
Cc:	linux-mm@...ck.org, Dave Chinner <david@...morbit.com>,
	Christoph Hellwig <hch@...radead.org>,
	Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Rik van Riel <riel@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>, Jan Kara <jack@...e.cz>,
	Andi Kleen <ak@...ux.intel.com>, linux-kernel@...r.kernel.org
Subject: Re: [patch 4/5] mm: writeback: throttle __GFP_WRITE on per-zone
 dirty limits

On Wed 03-08-11 22:25:00, Johannes Weiner wrote:
> On Wed, Jul 27, 2011 at 04:24:05PM +0200, Michal Hocko wrote:
> > On Mon 25-07-11 22:19:18, Johannes Weiner wrote:
> > [...]
> > > diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> > > index 41dc871..ce673ec 100644
> > > --- a/mm/page-writeback.c
> > > +++ b/mm/page-writeback.c
> > > @@ -378,6 +390,24 @@ int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
> > >  }
> > >  EXPORT_SYMBOL(bdi_set_max_ratio);
> > >  
> > > +static void sanitize_dirty_limits(unsigned long *pbackground,
> > > +				  unsigned long *pdirty)
> > > +{
> > > +	unsigned long background = *pbackground;
> > > +	unsigned long dirty = *pdirty;
> > > +	struct task_struct *tsk;
> > > +
> > > +	if (background >= dirty)
> > > +		background = dirty / 2;
> > > +	tsk = current;
> > > +	if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
> > > +		background += background / 4;
> > > +		dirty += dirty / 4;
> > > +	}
> > > +	*pbackground = background;
> > > +	*pdirty = dirty;
> > > +}
> > > +
> > >  /*
> > >   * global_dirty_limits - background-writeback and dirty-throttling thresholds
> > >   *
> > > @@ -389,33 +419,52 @@ EXPORT_SYMBOL(bdi_set_max_ratio);
> > >   */
> > >  void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
> > >  {
> > > -	unsigned long background;
> > > -	unsigned long dirty;
> > >  	unsigned long uninitialized_var(available_memory);
> > > -	struct task_struct *tsk;
> > >  
> > >  	if (!vm_dirty_bytes || !dirty_background_bytes)
> > >  		available_memory = determine_dirtyable_memory();
> > >  
> > >  	if (vm_dirty_bytes)
> > > -		dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
> > > +		*pdirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
> > >  	else
> > > -		dirty = (vm_dirty_ratio * available_memory) / 100;
> > > +		*pdirty = vm_dirty_ratio * available_memory / 100;
> > >  
> > >  	if (dirty_background_bytes)
> > > -		background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
> > > +		*pbackground = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
> > >  	else
> > > -		background = (dirty_background_ratio * available_memory) / 100;
> > > +		*pbackground = dirty_background_ratio * available_memory / 100;
> > >  
> > > -	if (background >= dirty)
> > > -		background = dirty / 2;
> > > -	tsk = current;
> > > -	if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
> > > -		background += background / 4;
> > > -		dirty += dirty / 4;
> > > -	}
> > > -	*pbackground = background;
> > > -	*pdirty = dirty;
> > > +	sanitize_dirty_limits(pbackground, pdirty);
> > > +}
> > 
> > Hmm, wouldn't be the patch little bit easier to read if this was
> > outside in a separate (cleanup) one?
> 
> I didn't find it hard to read.  But I wrote it, so... :)
> 
> Will split it out in the next round.  Thanks, Michal.

Thanks

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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