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, 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 E5754C433DB for ; Tue, 22 Dec 2020 08:00:28 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 7786423124 for ; Tue, 22 Dec 2020 08:00:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7786423124 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id B35956B006C; Tue, 22 Dec 2020 03:00:27 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id ABEFE6B0072; Tue, 22 Dec 2020 03:00:27 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 9607D6B0093; Tue, 22 Dec 2020 03:00:27 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0119.hostedemail.com [216.40.44.119]) by kanga.kvack.org (Postfix) with ESMTP id 7C8346B006C for ; Tue, 22 Dec 2020 03:00:27 -0500 (EST) Received: from smtpin20.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 391411DF9 for ; Tue, 22 Dec 2020 08:00:27 +0000 (UTC) X-FDA: 77620170894.20.guide08_39141d72745e Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin20.hostedemail.com (Postfix) with ESMTP id 04CFE180C0628 for ; Tue, 22 Dec 2020 08:00:26 +0000 (UTC) X-HE-Tag: guide08_39141d72745e X-Filterd-Recvd-Size: 3835 Received: from out4436.biz.mail.alibaba.com (out4436.biz.mail.alibaba.com [47.88.44.36]) by imf11.hostedemail.com (Postfix) with ESMTP for ; Tue, 22 Dec 2020 08:00:25 +0000 (UTC) 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: quoted-printable 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: Cc: Hui Su and Alexander Duyck as Hugh suggested. =D4=DA 2020/12/22 =CF=C2=CE=E71:20, Alex Shi =D0=B4=B5=C0: > 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(). >=20 > Hugh Dickin's polished the commit log, Thanks a lot! >=20 > 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(-) >=20 > 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 *pag= e) > struct lruvec *lruvec; > struct pglist_data *pgdat =3D page_pgdat(page); > =20 > - rcu_read_lock(); > lruvec =3D mem_cgroup_page_lruvec(page, pgdat); > spin_lock(&lruvec->lru_lock); > - rcu_read_unlock(); > =20 > lruvec_memcg_debug(lruvec, page); > =20 > @@ -1371,10 +1369,8 @@ struct lruvec *lock_page_lruvec_irq(struct page = *page) > struct lruvec *lruvec; > struct pglist_data *pgdat =3D page_pgdat(page); > =20 > - rcu_read_lock(); > lruvec =3D mem_cgroup_page_lruvec(page, pgdat); > spin_lock_irq(&lruvec->lru_lock); > - rcu_read_unlock(); > =20 > lruvec_memcg_debug(lruvec, page); > =20 > @@ -1386,10 +1382,8 @@ struct lruvec *lock_page_lruvec_irqsave(struct p= age *page, unsigned long *flags) > struct lruvec *lruvec; > struct pglist_data *pgdat =3D page_pgdat(page); > =20 > - rcu_read_lock(); > lruvec =3D mem_cgroup_page_lruvec(page, pgdat); > spin_lock_irqsave(&lruvec->lru_lock, *flags); > - rcu_read_unlock(); > =20 > lruvec_memcg_debug(lruvec, page); > =20 >=20