Re: [patch 2/5] mm: writeback: cleanups in preparation for per-zonedirty limits

[Michal Hocko]

On Fri 30-09-11 09:17:21, Johannes Weiner wrote:
> The next patch will introduce per-zone dirty limiting functions in
> addition to the traditional global dirty limiting.
> 
> Rename determine_dirtyable_memory() to global_dirtyable_memory()
> before adding the zone-specific version, and fix up its documentation.
> 
> Also, move the functions to determine the dirtyable memory and the
> function to calculate the dirty limit based on that together so that
> their relationship is more apparent and that they can be commented on
> as a group.
> 
> Signed-off-by: Johannes Weiner <jweiner@xxxxxxxxxx>
> Reviewed-by: Minchan Kim <minchan.kim@xxxxxxxxx>
> Acked-by: Mel Gorman <mel@xxxxxxx>

Reviewed-by: Michal Hocko <mhocko@xxxxxxx>

> ---
>  mm/page-writeback.c |   92 +++++++++++++++++++++++++-------------------------
>  1 files changed, 46 insertions(+), 46 deletions(-)
> 
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index c8acf8a..78604a6 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -186,12 +186,12 @@ static unsigned long highmem_dirtyable_memory(unsigned long total)
>  }
>  
>  /**
> - * determine_dirtyable_memory - amount of memory that may be used
> + * global_dirtyable_memory - number of globally dirtyable pages
>   *
> - * Returns the numebr of pages that can currently be freed and used
> - * by the kernel for direct mappings.
> + * Returns the global number of pages potentially available for dirty
> + * page cache.  This is the base value for the global dirty limits.
>   */
> -static unsigned long determine_dirtyable_memory(void)
> +static unsigned long global_dirtyable_memory(void)
>  {
>  	unsigned long x;
>  
> @@ -205,6 +205,47 @@ static unsigned long determine_dirtyable_memory(void)
>  }
>  
>  /*
> + * global_dirty_limits - background-writeback and dirty-throttling thresholds
> + *
> + * Calculate the dirty thresholds based on sysctl parameters
> + * - vm.dirty_background_ratio  or  vm.dirty_background_bytes
> + * - vm.dirty_ratio             or  vm.dirty_bytes
> + * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
> + * real-time tasks.
> + */
> +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 = global_dirtyable_memory();
> +
> +	if (vm_dirty_bytes)
> +		dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
> +	else
> +		dirty = (vm_dirty_ratio * available_memory) / 100;
> +
> +	if (dirty_background_bytes)
> +		background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
> +	else
> +		background = (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;
> +	trace_global_dirty_state(background, dirty);
> +}
> +
> +/*
>   * couple the period to the dirty_ratio:
>   *
>   *   period/2 ~ roundup_pow_of_two(dirty limit)
> @@ -216,7 +257,7 @@ static int calc_period_shift(void)
>  	if (vm_dirty_bytes)
>  		dirty_total = vm_dirty_bytes / PAGE_SIZE;
>  	else
> -		dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) /
> +		dirty_total = (vm_dirty_ratio * global_dirtyable_memory()) /
>  				100;
>  	return 2 + ilog2(dirty_total - 1);
>  }
> @@ -416,47 +457,6 @@ static unsigned long hard_dirty_limit(unsigned long thresh)
>  	return max(thresh, global_dirty_limit);
>  }
>  
> -/*
> - * global_dirty_limits - background-writeback and dirty-throttling thresholds
> - *
> - * Calculate the dirty thresholds based on sysctl parameters
> - * - vm.dirty_background_ratio  or  vm.dirty_background_bytes
> - * - vm.dirty_ratio             or  vm.dirty_bytes
> - * The dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
> - * real-time tasks.
> - */
> -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);
> -	else
> -		dirty = (vm_dirty_ratio * available_memory) / 100;
> -
> -	if (dirty_background_bytes)
> -		background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
> -	else
> -		background = (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;
> -	trace_global_dirty_state(background, dirty);
> -}
> -
>  /**
>   * bdi_dirty_limit - @bdi's share of dirty throttling threshold
>   * @bdi: the backing_dev_info to query
> -- 
> 1.7.6.2
> 
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-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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