Re: [PATCH 3/3] page-allocator: Move pcp static fields for high and batch off-pcp and onto the zone

[Nick Piggin]

On Tue, Aug 18, 2009 at 12:16:02PM +0100, Mel Gorman wrote:
> Having multiple lists per PCPU increased the size of the per-pcpu
> structure. Two of the fields, high and batch, do not change within a
> zone making that information redundant. This patch moves those fields
> off the PCP and onto the zone to reduce the size of the PCPU.

Hmm.. I did have some patches a long long time ago that among other
things made the lists larger for the local node only....

But I guess if something like that is ever shown to be a good idea
then we can go back to the old scheme. So yeah this seems OK.

> 
> Signed-off-by: Mel Gorman <mel@xxxxxxxxx>
> ---
>  include/linux/mmzone.h |    9 +++++----
>  mm/page_alloc.c        |   47 +++++++++++++++++++++++++----------------------
>  mm/vmstat.c            |    4 ++--
>  3 files changed, 32 insertions(+), 28 deletions(-)
> 
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 6e0b624..57a3ef0 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -167,12 +167,10 @@ enum zone_watermarks {
>  #define high_wmark_pages(z) (z->watermark[WMARK_HIGH])
>  
>  struct per_cpu_pages {
> -	int count;		/* number of pages in the list */
> -	int high;		/* high watermark, emptying needed */
> -	int batch;		/* chunk size for buddy add/remove */
> -
>  	/* Lists of pages, one per migrate type stored on the pcp-lists */
>  	struct list_head lists[MIGRATE_PCPTYPES];
> +
> +	int count;		/* number of pages in the list */
>  };
>  
>  struct per_cpu_pageset {
> @@ -284,6 +282,9 @@ struct zone {
>  	/* zone watermarks, access with *_wmark_pages(zone) macros */
>  	unsigned long watermark[NR_WMARK];
>  
> +	int pcp_high;		/* high watermark, emptying needed */
> +	int pcp_batch;		/* chunk size for buddy add/remove */
> +
>  	/*
>  	 * We don't know if the memory that we're going to allocate will be freeable
>  	 * or/and it will be released eventually, so to avoid totally wasting several
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index dd3f306..65cdfbf 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -988,8 +988,8 @@ void drain_zone_pages(struct zone *zone, struct per_cpu_pages *pcp)
>  	int to_drain;
>  
>  	local_irq_save(flags);
> -	if (pcp->count >= pcp->batch)
> -		to_drain = pcp->batch;
> +	if (pcp->count >= zone->pcp_batch)
> +		to_drain = zone->pcp_batch;
>  	else
>  		to_drain = pcp->count;
>  	free_pcppages_bulk(zone, to_drain, pcp);
> @@ -1129,9 +1129,9 @@ static void free_hot_cold_page(struct page *page, int cold)
>  	else
>  		list_add(&page->lru, &pcp->lists[migratetype]);
>  	pcp->count++;
> -	if (pcp->count >= pcp->high) {
> -		free_pcppages_bulk(zone, pcp->batch, pcp);
> -		pcp->count -= pcp->batch;
> +	if (pcp->count >= zone->pcp_high) {
> +		free_pcppages_bulk(zone, zone->pcp_batch, pcp);
> +		pcp->count -= zone->pcp_batch;
>  	}
>  
>  out:
> @@ -1199,7 +1199,7 @@ again:
>  		local_irq_save(flags);
>  		if (list_empty(list)) {
>  			pcp->count += rmqueue_bulk(zone, 0,
> -					pcp->batch, list,
> +					zone->pcp_batch, list,
>  					migratetype, cold);
>  			if (unlikely(list_empty(list)))
>  				goto failed;
> @@ -2178,8 +2178,8 @@ void show_free_areas(void)
>  			pageset = zone_pcp(zone, cpu);
>  
>  			printk("CPU %4d: hi:%5d, btch:%4d usd:%4d\n",
> -			       cpu, pageset->pcp.high,
> -			       pageset->pcp.batch, pageset->pcp.count);
> +			       cpu, zone->pcp_high,
> +			       zone->pcp_batch, pageset->pcp.count);
>  		}
>  	}
>  
> @@ -3045,7 +3045,9 @@ static int zone_batchsize(struct zone *zone)
>  #endif
>  }
>  
> -static void setup_pageset(struct per_cpu_pageset *p, unsigned long batch)
> +static void setup_pageset(struct zone *zone,
> +				struct per_cpu_pageset *p,
> +				unsigned long batch)
>  {
>  	struct per_cpu_pages *pcp;
>  	int migratetype;
> @@ -3054,8 +3056,8 @@ static void setup_pageset(struct per_cpu_pageset *p, unsigned long batch)
>  
>  	pcp = &p->pcp;
>  	pcp->count = 0;
> -	pcp->high = 6 * batch;
> -	pcp->batch = max(1UL, 1 * batch);
> +	zone->pcp_high = 6 * batch;
> +	zone->pcp_batch = max(1UL, 1 * batch);
>  	for (migratetype = 0; migratetype < MIGRATE_PCPTYPES; migratetype++)
>  		INIT_LIST_HEAD(&pcp->lists[migratetype]);
>  }
> @@ -3065,16 +3067,17 @@ static void setup_pageset(struct per_cpu_pageset *p, unsigned long batch)
>   * to the value high for the pageset p.
>   */
>  
> -static void setup_pagelist_highmark(struct per_cpu_pageset *p,
> +static void setup_pagelist_highmark(struct zone *zone,
> +				struct per_cpu_pageset *p,
>  				unsigned long high)
>  {
>  	struct per_cpu_pages *pcp;
>  
>  	pcp = &p->pcp;
> -	pcp->high = high;
> -	pcp->batch = max(1UL, high/4);
> +	zone->pcp_high = high;
> +	zone->pcp_batch = max(1UL, high/4);
>  	if ((high/4) > (PAGE_SHIFT * 8))
> -		pcp->batch = PAGE_SHIFT * 8;
> +		zone->pcp_batch = PAGE_SHIFT * 8;
>  }
>  
>  
> @@ -3115,10 +3118,10 @@ static int __cpuinit process_zones(int cpu)
>  		if (!zone_pcp(zone, cpu))
>  			goto bad;
>  
> -		setup_pageset(zone_pcp(zone, cpu), zone_batchsize(zone));
> +		setup_pageset(zone, zone_pcp(zone, cpu), zone_batchsize(zone));
>  
>  		if (percpu_pagelist_fraction)
> -			setup_pagelist_highmark(zone_pcp(zone, cpu),
> +			setup_pagelist_highmark(zone, zone_pcp(zone, cpu),
>  			 	(zone->present_pages / percpu_pagelist_fraction));
>  	}
>  
> @@ -3250,7 +3253,7 @@ static int __zone_pcp_update(void *data)
>  
>  		local_irq_save(flags);
>  		free_pcppages_bulk(zone, pcp->count, pcp);
> -		setup_pageset(pset, batch);
> +		setup_pageset(zone, pset, batch);
>  		local_irq_restore(flags);
>  	}
>  	return 0;
> @@ -3270,9 +3273,9 @@ static __meminit void zone_pcp_init(struct zone *zone)
>  #ifdef CONFIG_NUMA
>  		/* Early boot. Slab allocator not functional yet */
>  		zone_pcp(zone, cpu) = &boot_pageset[cpu];
> -		setup_pageset(&boot_pageset[cpu],0);
> +		setup_pageset(zone, &boot_pageset[cpu],0);
>  #else
> -		setup_pageset(zone_pcp(zone,cpu), batch);
> +		setup_pageset(zone, zone_pcp(zone,cpu), batch);
>  #endif
>  	}
>  	if (zone->present_pages)
> @@ -4781,7 +4784,7 @@ int lowmem_reserve_ratio_sysctl_handler(ctl_table *table, int write,
>  }
>  
>  /*
> - * percpu_pagelist_fraction - changes the pcp->high for each zone on each
> + * percpu_pagelist_fraction - changes the zone->pcp_high for each zone on each
>   * cpu.  It is the fraction of total pages in each zone that a hot per cpu pagelist
>   * can have before it gets flushed back to buddy allocator.
>   */
> @@ -4800,7 +4803,7 @@ int percpu_pagelist_fraction_sysctl_handler(ctl_table *table, int write,
>  		for_each_online_cpu(cpu) {
>  			unsigned long  high;
>  			high = zone->present_pages / percpu_pagelist_fraction;
> -			setup_pagelist_highmark(zone_pcp(zone, cpu), high);
> +			setup_pagelist_highmark(zone, zone_pcp(zone, cpu), high);
>  		}
>  	}
>  	return 0;
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index c81321f..a9d23c3 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -746,8 +746,8 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
>  			   "\n              batch: %i",
>  			   i,
>  			   pageset->pcp.count,
> -			   pageset->pcp.high,
> -			   pageset->pcp.batch);
> +			   zone->pcp_high,
> +			   zone->pcp_batch);
>  #ifdef CONFIG_SMP
>  		seq_printf(m, "\n  vm stats threshold: %d",
>  				pageset->stat_threshold);
> -- 
> 1.6.3.3
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