Re: [PATCH 1/2] mm: page_alloc: generalize the dirty balance reserve

[Michal Hocko]

On Mon 30-11-15 15:00:21, Johannes Weiner wrote:
> The dirty balance reserve that dirty throttling has to consider is
> merely memory not available to userspace allocations. There is nothing
> writeback-specific about it. Generalize the name so that it's reusable
> outside of that context.
> 
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>

Acked-by: Michal Hocko <mhocko@xxxxxxxx>

> ---
>  include/linux/mmzone.h |  6 +++---
>  include/linux/swap.h   |  1 -
>  mm/page-writeback.c    | 14 ++++++++++++--
>  mm/page_alloc.c        | 21 +++------------------
>  4 files changed, 18 insertions(+), 24 deletions(-)
> 
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index e23a9e7..9134ae3 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -361,10 +361,10 @@ struct zone {
>  	struct per_cpu_pageset __percpu *pageset;
>  
>  	/*
> -	 * This is a per-zone reserve of pages that should not be
> -	 * considered dirtyable memory.
> +	 * This is a per-zone reserve of pages that are not available
> +	 * to userspace allocations.
>  	 */
> -	unsigned long		dirty_balance_reserve;
> +	unsigned long		totalreserve_pages;
>  
>  #ifndef CONFIG_SPARSEMEM
>  	/*
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 7ba7dcc..066bd21 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -287,7 +287,6 @@ static inline void workingset_node_shadows_dec(struct radix_tree_node *node)
>  /* linux/mm/page_alloc.c */
>  extern unsigned long totalram_pages;
>  extern unsigned long totalreserve_pages;
> -extern unsigned long dirty_balance_reserve;
>  extern unsigned long nr_free_buffer_pages(void);
>  extern unsigned long nr_free_pagecache_pages(void);
>  
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 2c90357..8e5f2fd 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -278,7 +278,12 @@ static unsigned long zone_dirtyable_memory(struct zone *zone)
>  	unsigned long nr_pages;
>  
>  	nr_pages = zone_page_state(zone, NR_FREE_PAGES);
> -	nr_pages -= min(nr_pages, zone->dirty_balance_reserve);
> +	/*
> +	 * Pages reserved for the kernel should not be considered
> +	 * dirtyable, to prevent a situation where reclaim has to
> +	 * clean pages in order to balance the zones.
> +	 */
> +	nr_pages -= min(nr_pages, zone->totalreserve_pages);
>  
>  	nr_pages += zone_page_state(zone, NR_INACTIVE_FILE);
>  	nr_pages += zone_page_state(zone, NR_ACTIVE_FILE);
> @@ -332,7 +337,12 @@ static unsigned long global_dirtyable_memory(void)
>  	unsigned long x;
>  
>  	x = global_page_state(NR_FREE_PAGES);
> -	x -= min(x, dirty_balance_reserve);
> +	/*
> +	 * Pages reserved for the kernel should not be considered
> +	 * dirtyable, to prevent a situation where reclaim has to
> +	 * clean pages in order to balance the zones.
> +	 */
> +	x -= min(x, totalreserve_pages);
>  
>  	x += global_page_state(NR_INACTIVE_FILE);
>  	x += global_page_state(NR_ACTIVE_FILE);
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 17a3c66..e786d7e 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -114,13 +114,6 @@ static DEFINE_SPINLOCK(managed_page_count_lock);
>  unsigned long totalram_pages __read_mostly;
>  unsigned long totalreserve_pages __read_mostly;
>  unsigned long totalcma_pages __read_mostly;
> -/*
> - * When calculating the number of globally allowed dirty pages, there
> - * is a certain number of per-zone reserves that should not be
> - * considered dirtyable memory.  This is the sum of those reserves
> - * over all existing zones that contribute dirtyable memory.
> - */
> -unsigned long dirty_balance_reserve __read_mostly;
>  
>  int percpu_pagelist_fraction;
>  gfp_t gfp_allowed_mask __read_mostly = GFP_BOOT_MASK;
> @@ -5955,20 +5948,12 @@ static void calculate_totalreserve_pages(void)
>  
>  			if (max > zone->managed_pages)
>  				max = zone->managed_pages;
> +
> +			zone->totalreserve_pages = max;
> +
>  			reserve_pages += max;
> -			/*
> -			 * Lowmem reserves are not available to
> -			 * GFP_HIGHUSER page cache allocations and
> -			 * kswapd tries to balance zones to their high
> -			 * watermark.  As a result, neither should be
> -			 * regarded as dirtyable memory, to prevent a
> -			 * situation where reclaim has to clean pages
> -			 * in order to balance the zones.
> -			 */
> -			zone->dirty_balance_reserve = max;
>  		}
>  	}
> -	dirty_balance_reserve = reserve_pages;
>  	totalreserve_pages = reserve_pages;
>  }
>  
> -- 
> 2.6.2
> 
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-- 
Michal Hocko
SUSE Labs
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