From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: 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 B44E6C433DF for ; Mon, 20 Jul 2020 23:14:34 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 713BE208E4 for ; Mon, 20 Jul 2020 23:14:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="pPjPEhTN" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 713BE208E4 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id BEA846B0003; Mon, 20 Jul 2020 19:14:33 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B9C076B0008; Mon, 20 Jul 2020 19:14:33 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id AB3646B000D; Mon, 20 Jul 2020 19:14:33 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0194.hostedemail.com [216.40.44.194]) by kanga.kvack.org (Postfix) with ESMTP id 92C3C6B0003 for ; Mon, 20 Jul 2020 19:14:33 -0400 (EDT) Received: from smtpin05.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 20795181AEF31 for ; Mon, 20 Jul 2020 23:14:33 +0000 (UTC) X-FDA: 77060010426.05.blade15_3d0857c26f28 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin05.hostedemail.com (Postfix) with ESMTP id E4FED1801BD81 for ; Mon, 20 Jul 2020 23:14:05 +0000 (UTC) X-HE-Tag: blade15_3d0857c26f28 X-Filterd-Recvd-Size: 2168 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf27.hostedemail.com (Postfix) with ESMTP for ; Mon, 20 Jul 2020 23:14:05 +0000 (UTC) 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 To: Alex Shi 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 X-Rspamd-Queue-Id: E4FED1801BD81 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, 20 Jul 2020 13:42:45 +0800 Alex Shi 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?