linux-kernel - Re: [PATCH] cpuset: mm: Reduce large amounts of memory barrier related damage v3

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Message-ID: <521AE884.6090605@redhat.com>
Date:	Mon, 26 Aug 2013 01:32:52 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Miao Xie <miaox@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>,
	Christoph Lameter <cl@...ux.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpuset: mm: Reduce large amounts of memory barrier related
 damage v3

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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