From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <SRS0=bl3x=A7=vger.kernel.org=linux-kernel-owner@kernel.org>
X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on
	aws-us-west-2-korg-lkml-1.web.codeaurora.org
X-Spam-Level: 
X-Spam-Status: No, score=-4.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH,
	DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,
	NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no
	version=3.4.0
Received: from mail.kernel.org (mail.kernel.org [198.145.29.99])
	by smtp.lore.kernel.org (Postfix) with ESMTP id DD5B5C433E0
	for <linux-kernel@archiver.kernel.org>; Mon, 20 Jul 2020 23:14:06 +0000 (UTC)
Received: from vger.kernel.org (vger.kernel.org [23.128.96.18])
	by mail.kernel.org (Postfix) with ESMTP id AB9DE22B4E
	for <linux-kernel@archiver.kernel.org>; Mon, 20 Jul 2020 23:14:06 +0000 (UTC)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org;
	s=default; t=1595286846;
	bh=Cp16k7Wc92Ppe/2CQspapK5SPF4JM2qVE09ioyCdbwg=;
	h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From;
	b=coGcz025qN05FDe4LHg73Hh6L4AebLzeKCwazYULfoOjRAZcld8Jf5YOD2BQHwZVT
	 5H/iXvVme/GDWpwIwTBXJGKY9oAE4qO3vDF9JwmAlv+k7z9aqBPk2FaJKz0b0Iqeup
	 2oJUtm/gpb5zyWx3k8sry5FmRGcKirenBMKinNyw=
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1726691AbgGTXOF (ORCPT
        <rfc822;linux-kernel@archiver.kernel.org>);
        Mon, 20 Jul 2020 19:14:05 -0400
Received: from mail.kernel.org ([198.145.29.99]:43078 "EHLO mail.kernel.org"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1726109AbgGTXOF (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Mon, 20 Jul 2020 19:14:05 -0400
Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41])
        (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
        (No client certificate requested)
        by mail.kernel.org (Postfix) with ESMTPSA id 6E9D0208E4;
        Mon, 20 Jul 2020 23:14:04 +0000 (UTC)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org;
        s=default; t=1595286844;
        bh=Cp16k7Wc92Ppe/2CQspapK5SPF4JM2qVE09ioyCdbwg=;
        h=Date:From:To:Cc:Subject:In-Reply-To:References:From;
        b=pPjPEhTNM3NC8uYRQxLQciU+ByEWOMRUsMMl73rU1hir+vIucZ3HYL8M6c/nr54oN
         VlBDgaEWPC3LPSGKk+/z6xfOzVLnrWOARZOtU/fQade44Ldk8eHJgTRfRKlXgNni2y
         gfjyoQXVdJYx5VHNKap6QhWL3KPnQZLoZElZKoFQ=
Date:   Mon, 20 Jul 2020 16:14:04 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Alex Shi <alex.shi@linux.alibaba.com>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/vmstat: don't do count if no needs
Message-Id: <20200720161404.bd0c24560114bf48d6acbaff@linux-foundation.org>
In-Reply-To: <1ef9baa0-9788-5917-2590-a8c3fc593b81@linux.alibaba.com>
References: <20200720052348.428564-1-alex.shi@linux.alibaba.com>
        <1ef9baa0-9788-5917-2590-a8c3fc593b81@linux.alibaba.com>
X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu)
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Mon, 20 Jul 2020 13:42:45 +0800 Alex Shi <alex.shi@linux.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?