Re: [PATCH] Fix handling of pagesets for downed cpus

[KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>]

> After downing/upping a cpu, an attempt to set
> /proc/sys/vm/percpu_pagelist_fraction results in an oops in
> percpu_pagelist_fraction_sysctl_handler().
> 
> If a processor is downed then we need to set the pageset pointer back to the
> boot pageset.
> 
> Updates of the high water marks should not access pagesets of unpopulated zones
> (those pointer go to the boot pagesets which would be no longer functional if
> their size would be increased beyond zero).
> 
> Signed-off-by: Dimitri Sivanich <sivanich@sgi.com>
> Signed-off-by: Christoph Lameter <cl@linux-foundation.org>
> 
> ---
> 
> This patch should go into the -stable tree as well.
> 
>  mm/page_alloc.c |    6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> Index: linux/mm/page_alloc.c
> ===================================================================
> --- linux.orig/mm/page_alloc.c	2009-06-22 13:06:50.000000000 -0500
> +++ linux/mm/page_alloc.c	2009-06-22 13:08:09.000000000 -0500
> @@ -3026,7 +3026,7 @@ bad:
>  		if (dzone == zone)
>  			break;
>  		kfree(zone_pcp(dzone, cpu));
> -		zone_pcp(dzone, cpu) = NULL;
> +		zone_pcp(dzone, cpu) = &boot_pageset[cpu];
>  	}
>  	return -ENOMEM;
>  }
> @@ -3041,7 +3041,7 @@ static inline void free_zone_pagesets(in
>  		/* Free per_cpu_pageset if it is slab allocated */
>  		if (pset != &boot_pageset[cpu])
>  			kfree(pset);
> -		zone_pcp(zone, cpu) = NULL;
> +		zone_pcp(zone, cpu) = &boot_pageset[cpu];
>  	}
>  }
>  
> @@ -4659,7 +4659,7 @@ int percpu_pagelist_fraction_sysctl_hand
>  	ret = proc_dointvec_minmax(table, write, file, buffer, length, ppos);
>  	if (!write || (ret == -EINVAL))
>  		return ret;
> -	for_each_zone(zone) {
> +	for_each_populated_zone(zone) {
>  		for_each_online_cpu(cpu) {
>  			unsigned long  high;
>  			high = zone->present_pages / percpu_pagelist_fraction;

Looks good. thanks for making multiple improvement.

	Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>