linux-kernel - Re: [PATCH 08/22] mm/vmstat: Avoid on each online CPU loops

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Date:   Mon, 28 Nov 2016 10:28:01 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, rt@...utronix.de, tglx@...utronix.de,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org
Subject: Re: [PATCH 08/22] mm/vmstat: Avoid on each online CPU loops

On Sun 27-11-16 00:13:36, Sebastian Andrzej Siewior wrote:
[...]
>  static void __init init_cpu_node_state(void)
>  {
> -	int cpu;
> +	int node;
>  
> -	for_each_online_cpu(cpu)
> -		node_set_state(cpu_to_node(cpu), N_CPU);
> +	for_each_online_node(node)
> +		node_set_state(node, N_CPU);

Is this really correct? The point of the original code was to mark only
those nodes which have at least one CPU. Or am I missing something?

>  }
>  
>  static void vmstat_cpu_dead(int node)
>  {
> -	int cpu;
> +	const struct cpumask *node_cpus;
>  
> -	for_each_online_cpu(cpu)
> -		if (cpu_to_node(cpu) == node)
> -			return;
> +	node_cpus = cpumask_of_node(node);
> +	if (cpumask_weight(node_cpus) > 0)
> +		return;

This looks OK

>  
>  	node_clear_state(node, N_CPU);
>  }
> -- 
> 2.10.2
> 
> --
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-- 
Michal Hocko
SUSE Labs