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

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Date:	Wed, 27 Jul 2011 16:24:05 +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 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?

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