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=-17.8 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, URIBL_BLOCKED,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 BE205C433DB for ; Tue, 22 Dec 2020 08:01:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8990A22D57 for ; Tue, 22 Dec 2020 08:01:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725912AbgLVIBF (ORCPT ); Tue, 22 Dec 2020 03:01:05 -0500 Received: from out30-54.freemail.mail.aliyun.com ([115.124.30.54]:40078 "EHLO out30-54.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725300AbgLVIBF (ORCPT ); Tue, 22 Dec 2020 03:01:05 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R781e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e01424;MF=alex.shi@linux.alibaba.com;NM=1;PH=DS;RN=10;SR=0;TI=SMTPD_---0UJQTnsf_1608624020; Received: from IT-FVFX43SYHV2H.local(mailfrom:alex.shi@linux.alibaba.com fp:SMTPD_---0UJQTnsf_1608624020) by smtp.aliyun-inc.com(127.0.0.1); Tue, 22 Dec 2020 16:00:20 +0800 Subject: Re: [PATCH v2 2/3] mm/memcg: remove rcu locking for lock_page_lruvec function series From: Alex Shi To: hughd@google.com Cc: Johannes Weiner , Michal Hocko , Vladimir Davydov , Andrew Morton , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hui Su , Alexander Duyck References: <1608614453-10739-1-git-send-email-alex.shi@linux.alibaba.com> <1608614453-10739-2-git-send-email-alex.shi@linux.alibaba.com> Message-ID: <398f089d-250b-39f7-691a-9ce495b30700@linux.alibaba.com> Date: Tue, 22 Dec 2020 16:00:20 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.0; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <1608614453-10739-2-git-send-email-alex.shi@linux.alibaba.com> Content-Type: text/plain; charset=gbk Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Cc: Hui Su and Alexander Duyck as Hugh suggested. ÔÚ 2020/12/22 ÏÂÎç1:20, Alex Shi дµÀ: > lock_page_lruvec() and its variants used rcu_read_lock() with the > intention of safeguarding against the mem_cgroup being destroyed > concurrently; but so long as they are called under the specified > conditions (as they are), there is no way for the page's mem_cgroup > to be destroyed. Delete the unnecessary rcu_read_lock() and _unlock(). > > Hugh Dickin's polished the commit log, Thanks a lot! > > Signed-off-by: Alex Shi > Acked-by: Hugh Dickins > Cc: Hugh Dickins > Cc: Johannes Weiner > Cc: Michal Hocko > Cc: Vladimir Davydov > Cc: Andrew Morton > Cc: cgroups@vger.kernel.org > Cc: linux-mm@kvack.org > Cc: linux-kernel@vger.kernel.org > --- > mm/memcontrol.c | 6 ------ > 1 file changed, 6 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 8d400efc81b9..0af13c4fe4b3 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -1356,10 +1356,8 @@ struct lruvec *lock_page_lruvec(struct page *page) > struct lruvec *lruvec; > struct pglist_data *pgdat = page_pgdat(page); > > - rcu_read_lock(); > lruvec = mem_cgroup_page_lruvec(page, pgdat); > spin_lock(&lruvec->lru_lock); > - rcu_read_unlock(); > > lruvec_memcg_debug(lruvec, page); > > @@ -1371,10 +1369,8 @@ struct lruvec *lock_page_lruvec_irq(struct page *page) > struct lruvec *lruvec; > struct pglist_data *pgdat = page_pgdat(page); > > - rcu_read_lock(); > lruvec = mem_cgroup_page_lruvec(page, pgdat); > spin_lock_irq(&lruvec->lru_lock); > - rcu_read_unlock(); > > lruvec_memcg_debug(lruvec, page); > > @@ -1386,10 +1382,8 @@ struct lruvec *lock_page_lruvec_irqsave(struct page *page, unsigned long *flags) > struct lruvec *lruvec; > struct pglist_data *pgdat = page_pgdat(page); > > - rcu_read_lock(); > lruvec = mem_cgroup_page_lruvec(page, pgdat); > spin_lock_irqsave(&lruvec->lru_lock, *flags); > - rcu_read_unlock(); > > lruvec_memcg_debug(lruvec, page); > >