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Date: Mon, 26 Aug 2013 01:32:52 -0400
From: Rik van Riel <riel@redhat.com>
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To: Peter Zijlstra <peterz@infradead.org>
CC: Mel Gorman <mgorman@suse.de>, Andrew Morton <akpm@linux-foundation.org>,
        Miao Xie <miaox@cn.fujitsu.com>, David Rientjes <rientjes@google.com>,
        Christoph Lameter <cl@linux.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] cpuset: mm: Reduce large amounts of memory barrier related
 damage v3
References: <20120307180852.GE17697@suse.de> <20130823130332.GY31370@twins.programming.kicks-ass.net> <20130823181546.GA31370@twins.programming.kicks-ass.net>
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On 08/23/2013 02:15 PM, Peter Zijlstra wrote:

> So I guess the quick and ugly solution is something like the below. 

This still crashes :)

> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -1762,19 +1762,21 @@ unsigned slab_node(void)
>  static unsigned offset_il_node(struct mempolicy *pol,
>  		struct vm_area_struct *vma, unsigned long off)
>  {
> -	unsigned nnodes = nodes_weight(pol->v.nodes);
> -	unsigned target;
> -	int c;
> -	int nid = -1;
> +	unsigned nnodes, target;
> +	int c, nid;
>  
> +again:
> +	nnodes = nodes_weight(pol->v.nodes);
>  	if (!nnodes)
>  		return numa_node_id();
> +
>  	target = (unsigned int)off % nnodes;
> -	c = 0;
> -	do {
> +	for (c = 0, nid = -1; c <= target; c++)
>  		nid = next_node(nid, pol->v.nodes);
> -		c++;
> -	} while (c <= target);
> +
> +	if (unlikely((unsigned)nid >= MAX_NUMNODES))
> +		goto again;

I'll go kick off a compile that replaces the conditional above with:

	if (unlikely(!node_online(nid)))
		goto again;

>  	return nid;
>  }


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