linux-kernel - Re: cpusets: randomize node rotor used in cpuset_mem_spread

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Date:	Thu, 14 Apr 2011 11:19:24 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	kosaki.motohiro@...fujitsu.com,
	LKML <linux-kernel@...r.kernel.org>,
	Jack Steiner <steiner@....com>,
	Lee Schermerhorn <lee.schermerhorn@...com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Paul Menage <menage@...gle.com>, Robin Holt <holt@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: cpusets: randomize node rotor used in cpuset_mem_spread_node()

> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 959a8b8..8e57a72 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -93,6 +93,7 @@
>  
>  #include <asm/tlbflush.h>
>  #include <asm/uaccess.h>
> +#include <linux/random.h>
>  
>  #include "internal.h"
>  
> @@ -1649,6 +1650,21 @@ static inline unsigned interleave_nid(struct mempolicy *pol,
>  		return interleave_nodes(pol);
>  }
>  
> +/*
> + * Return the bit number of a random bit set in the nodemask.
> + * (returns -1 if nodemask is empty)
> + */
> +int node_random(const nodemask_t *maskp)
> +{
> +	int w, bit = -1;
> +
> +	w = nodes_weight(*maskp);
> +	if (w)
> +		bit = bitmap_ord_to_pos(maskp->bits,
> +			get_random_int() % w, MAX_NUMNODES);
> +	return bit;
> +}
> +
>  #ifdef CONFIG_HUGETLBFS
>  /*
>   * huge_zonelist(@vma, @addr, @gfp_flags, @mpol)

mempolicy.c is no best place for putting generic nodemask utility function.
but unforunately we have no alternative. Gack.
	Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>



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