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

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Message-ID: <20110803202500.GA8286@redhat.com>
Date:	Wed, 3 Aug 2011 22:25:00 +0200
From:	Johannes Weiner <jweiner@...hat.com>
To:	Michal Hocko <mhocko@...e.cz>
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, 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.
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