linux-kernel - Re: [PATCH] mm/vmstat: don't do count if no needs

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Message-Id: <20200720161404.bd0c24560114bf48d6acbaff@linux-foundation.org>
Date:   Mon, 20 Jul 2020 16:14:04 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Alex Shi <alex.shi@...ux.alibaba.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/vmstat: don't do count if no needs

On Mon, 20 Jul 2020 13:42:45 +0800 Alex Shi <alex.shi@...ux.alibaba.com> wrote:

> 
> For couple of vmstat account funcs, the caller usually doesn't check the
> delta value, if delta == 0, irq or atomic operator is a waste. That's
> better to be skipped, also add unlikey() since !delta is less happened.
> 
> ...
>
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -321,6 +321,9 @@ void __mod_zone_page_state(struct zone *zone, enum zone_stat_item item,
>  	long x;
>  	long t;
>  
> +	if (unlikely(!delta))
> +		return;
> +

Do we know that delta==0 is frequent enough to make the change a net
benefit?