linux-kernel - Re: [PATCH 24/49] mm/vmstat: replace cpumask_weight with cpumask

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Date:   Fri, 11 Feb 2022 12:39:47 +0200
From:   Mike Rapoport <rppt@...nel.org>
To:     Yury Norov <yury.norov@...il.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        David Laight <David.Laight@...lab.com>,
        Joe Perches <joe@...ches.com>, Dennis Zhou <dennis@...nel.org>,
        Emil Renner Berthing <kernel@...il.dk>,
        Nicholas Piggin <npiggin@...il.com>,
        Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
        Alexey Klimov <aklimov@...hat.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 24/49] mm/vmstat: replace cpumask_weight with
 cpumask_empty where appropriate

On Thu, Feb 10, 2022 at 02:49:08PM -0800, Yury Norov wrote:
> mm/vmstat.c code calls cpumask_weight() to check if any bit of a given
> cpumask is set. We can do it more efficiently with cpumask_empty() because
> cpumask_empty() stops traversing the cpumask as soon as it finds first set
> bit, while cpumask_weight() counts all bits unconditionally.
> 
> Signed-off-by: Yury Norov <yury.norov@...il.com>

Acked-by: Mike Rapoport <rppt@...ux.ibm.com>

> ---
>  mm/vmstat.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index d5cc8d739fac..27a94afd4ee5 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -2041,7 +2041,7 @@ static void __init init_cpu_node_state(void)
>  	int node;
>  
>  	for_each_online_node(node) {
> -		if (cpumask_weight(cpumask_of_node(node)) > 0)
> +		if (!cpumask_empty(cpumask_of_node(node)))
>  			node_set_state(node, N_CPU);
>  	}
>  }
> @@ -2068,7 +2068,7 @@ static int vmstat_cpu_dead(unsigned int cpu)
>  
>  	refresh_zone_stat_thresholds();
>  	node_cpus = cpumask_of_node(node);
> -	if (cpumask_weight(node_cpus) > 0)
> +	if (!cpumask_empty(node_cpus))
>  		return 0;
>  
>  	node_clear_state(node, N_CPU);
> -- 
> 2.32.0
> 
> 

-- 
Sincerely yours,
Mike.