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Date:	Sun, 07 Apr 2013 09:56:18 +0800
From:	Simon Jeons <simon.jeons@...il.com>
To:	Cody P Schafer <cody@...ux.vnet.ibm.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Linux MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] mm: when handling percpu_pagelist_fraction, use on_each_cpu()
 to set percpu pageset fields.

Hi Cody,
On 04/06/2013 04:33 AM, Cody P Schafer wrote:
> In free_hot_cold_page(), we rely on pcp->batch remaining stable.
> Updating it without being on the cpu owning the percpu pageset
> potentially destroys this stability.

If cpu is off, can its pcp pageset be used in free_hot_code_page()?

>
> Change for_each_cpu() to on_each_cpu() to fix.
>
> Signed-off-by: Cody P Schafer <cody@...ux.vnet.ibm.com>
> ---
>   mm/page_alloc.c | 21 +++++++++++----------
>   1 file changed, 11 insertions(+), 10 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 48f2faa..507db31 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5475,30 +5475,31 @@ int lowmem_reserve_ratio_sysctl_handler(ctl_table *table, int write,
>   	return 0;
>   }
>   
> +static void _zone_set_pageset_highmark(void *data)
> +{
> +	struct zone *zone = data;
> +	unsigned long  high;
> +	high = zone->managed_pages / percpu_pagelist_fraction;
> +	setup_pagelist_highmark(
> +			per_cpu_ptr(zone->pageset, smp_processor_id()), high);
> +}
> +
>   /*
>    * percpu_pagelist_fraction - changes the 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.
>    */
> -
>   int percpu_pagelist_fraction_sysctl_handler(ctl_table *table, int write,
>   	void __user *buffer, size_t *length, loff_t *ppos)
>   {
>   	struct zone *zone;
> -	unsigned int cpu;
>   	int ret;
>   
>   	ret = proc_dointvec_minmax(table, write, buffer, length, ppos);
>   	if (!write || (ret < 0))
>   		return ret;
> -	for_each_populated_zone(zone) {
> -		for_each_possible_cpu(cpu) {
> -			unsigned long  high;
> -			high = zone->managed_pages / percpu_pagelist_fraction;
> -			setup_pagelist_highmark(
> -				per_cpu_ptr(zone->pageset, cpu), high);
> -		}
> -	}
> +	for_each_populated_zone(zone)
> +		on_each_cpu(_zone_set_pageset_highmark, zone, true);
>   	return 0;
>   }
>   

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