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=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 192C9C56201 for ; Sat, 28 Nov 2020 04:31:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AD0F721534 for ; Sat, 28 Nov 2020 04:31:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="JAALZCsu" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732515AbgK1Eaz (ORCPT ); Fri, 27 Nov 2020 23:30:55 -0500 Received: from mail.kernel.org ([198.145.29.99]:54698 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731107AbgK1E0P (ORCPT ); Fri, 27 Nov 2020 23:26:15 -0500 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 AE87822210; Sat, 28 Nov 2020 04:02:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1606536139; bh=cEMGKa+zaxvHsRTKQlwMDDceDlj0bM6QUnQtUx0U94c=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=JAALZCsu2JDfiEM8zsNRQXwSeYlLs10hrPu3LQgqgHaCQf7jTRXkxTF+UxLNcJQU9 fd83a8RvMdiCYjGXuARb2VEaYNdZKJrNzETQjq7U/saO8xsyVSdhWOHW38Cx+8Qmo8 E+ayM46ekK+b369uO9g7eeBP8IkN7SilD8RrPd1I= Date: Fri, 27 Nov 2020 20:02:15 -0800 From: Andrew Morton To: Alex Shi Cc: Johannes Weiner , Shakeel Butt , Roman Gushchin , Lorenzo Stoakes , Stephen Rothwell , Alexander Duyck , Yafang Shao , Wei Yang , linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/memcg: bail out early when !memcg in mem_cgroup_lruvec Message-Id: <20201127200215.dc96a839cdd816361e7093e6@linux-foundation.org> In-Reply-To: <1606446515-36069-1-git-send-email-alex.shi@linux.alibaba.com> References: <1606446515-36069-1-git-send-email-alex.shi@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 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 27 Nov 2020 11:08:35 +0800 Alex Shi wrote: > Sometime, we use NULL memcg in mem_cgroup_lruvec(memcg, pgdat) > so we could get out early in the situation to avoid useless checking. > > Also warning if both parameter are NULL. Why do you think a warning is needed here? > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -613,14 +613,13 @@ static inline struct lruvec *mem_cgroup_lruvec(struct mem_cgroup *memcg, > struct mem_cgroup_per_node *mz; > struct lruvec *lruvec; > > - if (mem_cgroup_disabled()) { > + VM_WARN_ON_ONCE(!memcg && !pgdat); > + > + if (mem_cgroup_disabled() || !memcg) { > lruvec = &pgdat->__lruvec; > goto out; > } > > - if (!memcg) > - memcg = root_mem_cgroup; > - This change isn't obviously equivalent, is it? > mz = mem_cgroup_nodeinfo(memcg, pgdat->node_id); > lruvec = &mz->lruvec; > out: And the resulting code is awkward: if (mem_cgroup_disabled() || !memcg) { lruvec = &pgdat->__lruvec; goto out; } mz = mem_cgroup_nodeinfo(memcg, pgdat->node_id); lruvec = &mz->lruvec; out: could be if (mem_cgroup_disabled() || !memcg) { lruvec = &pgdat->__lruvec; } else { mem_cgroup_per_node mz; mz = mem_cgroup_nodeinfo(memcg, pgdat->node_id); lruvec = &mz->lruvec; }