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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY, USER_AGENT_SANE_1 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 81433C3E8C5 for ; Sun, 29 Nov 2020 04:45:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3EA1520825 for ; Sun, 29 Nov 2020 04:45:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726504AbgK2Eom (ORCPT ); Sat, 28 Nov 2020 23:44:42 -0500 Received: from out30-57.freemail.mail.aliyun.com ([115.124.30.57]:58061 "EHLO out30-57.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726006AbgK2Eol (ORCPT ); Sat, 28 Nov 2020 23:44:41 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R141e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04407;MF=alex.shi@linux.alibaba.com;NM=1;PH=DS;RN=10;SR=0;TI=SMTPD_---0UGqPWhq_1606625033; Received: from IT-FVFX43SYHV2H.local(mailfrom:alex.shi@linux.alibaba.com fp:SMTPD_---0UGqPWhq_1606625033) by smtp.aliyun-inc.com(127.0.0.1); Sun, 29 Nov 2020 12:43:53 +0800 Subject: Re: [PATCH] mm/memcg: bail out early when !memcg in mem_cgroup_lruvec To: Andrew Morton Cc: Johannes Weiner , Shakeel Butt , Roman Gushchin , Lorenzo Stoakes , Stephen Rothwell , Alexander Duyck , Yafang Shao , Wei Yang , linux-kernel@vger.kernel.org References: <1606446515-36069-1-git-send-email-alex.shi@linux.alibaba.com> <20201127200215.dc96a839cdd816361e7093e6@linux-foundation.org> From: Alex Shi Message-ID: <9ddb17cd-cf5f-15b1-6a7d-986ee44fd5df@linux.alibaba.com> Date: Sun, 29 Nov 2020 12:43:52 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <20201127200215.dc96a839cdd816361e7093e6@linux-foundation.org> Content-Type: text/plain; charset=gbk Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ÔÚ 2020/11/28 ÏÂÎç12:02, Andrew Morton дµÀ: > 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? Uh, Consider there are no problem for long time, it could be saved. > >> --- 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? If !memcg, the root_mem_cgroup will still lead the lruvec to a pgdat same as parameter. > >> 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; > } > Right. remove 'goto' is better for understander. So, is the following patch ok? >From 225f29e03b40a7cbaeb4e3bb76f8efbcd7d648a2 Mon Sep 17 00:00:00 2001 From: Alex Shi Date: Wed, 25 Nov 2020 14:06:33 +0800 Subject: [PATCH v2] mm/memcg: bail out early when !memcg in mem_cgroup_lruvec Sometime, we use NULL memcg in mem_cgroup_lruvec(memcg, pgdat) so we could get out early in the situation to avoid useless checking. Polished as Andrew Morton's suggestion. Signed-off-by: Alex Shi Cc: Andrew Morton Cc: Johannes Weiner Cc: Shakeel Butt Cc: Roman Gushchin Cc: Lorenzo Stoakes Cc: Stephen Rothwell Cc: Alexander Duyck Cc: Yafang Shao Cc: Wei Yang Cc: linux-kernel@vger.kernel.org --- include/linux/memcontrol.h | 15 ++++++--------- 1 file changed, 6 insertions(+), 9 deletions(-) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 3e6a1df3bdb9..4ff2ffe2b73d 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -610,20 +610,17 @@ mem_cgroup_nodeinfo(struct mem_cgroup *memcg, int nid) static inline struct lruvec *mem_cgroup_lruvec(struct mem_cgroup *memcg, struct pglist_data *pgdat) { - struct mem_cgroup_per_node *mz; struct lruvec *lruvec; - if (mem_cgroup_disabled()) { + if (mem_cgroup_disabled() || !memcg) { lruvec = &pgdat->__lruvec; - goto out; - } + } else { + struct mem_cgroup_per_node *mz; - if (!memcg) - memcg = root_mem_cgroup; + mz = mem_cgroup_nodeinfo(memcg, pgdat->node_id); + lruvec = &mz->lruvec; + } - mz = mem_cgroup_nodeinfo(memcg, pgdat->node_id); - lruvec = &mz->lruvec; -out: /* * Since a node can be onlined after the mem_cgroup was created, * we have to be prepared to initialize lruvec->pgdat here; -- 2.29.GIT