linux-kernel - Re: [PATCH 7/8] sched: Split accounting of NUMA hinting faults that pass two-stage filter

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Date:	Thu, 27 Jun 2013 16:56:58 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 7/8] sched: Split accounting of NUMA hinting faults that
 pass two-stage filter

On Wed, Jun 26, 2013 at 03:38:06PM +0100, Mel Gorman wrote:
> +void task_numa_fault(int last_nid, int node, int pages, bool migrated)
>  {
>  	struct task_struct *p = current;
> +	int priv = (cpu_to_node(task_cpu(p)) == last_nid);
>  
>  	if (!sched_feat_numa(NUMA))
>  		return;
>  
>  	/* Allocate buffer to track faults on a per-node basis */
>  	if (unlikely(!p->numa_faults)) {
> -		int size = sizeof(*p->numa_faults) * nr_node_ids;
> +		int size = sizeof(*p->numa_faults) * 2 * nr_node_ids;
>  
>  		/* numa_faults and numa_faults_buffer share the allocation */
> -		p->numa_faults = kzalloc(size * 2, GFP_KERNEL);
> +		p->numa_faults = kzalloc(size * 4, GFP_KERNEL);
>  		if (!p->numa_faults)
>  			return;

So you need a buffer 2x the size in total; but you're now allocating
a buffer 4x larger than before.

Isn't doubling size alone sufficient?
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