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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,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 8AE5EC432C0 for ; Tue, 19 Nov 2019 10:04:44 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 516B320857 for ; Tue, 19 Nov 2019 10:04:44 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 516B320857 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 BFAD56B0271; Tue, 19 Nov 2019 05:04:43 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id BAAB16B0272; Tue, 19 Nov 2019 05:04:43 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id AE8F36B0274; Tue, 19 Nov 2019 05:04:43 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0097.hostedemail.com [216.40.44.97]) by kanga.kvack.org (Postfix) with ESMTP id 983306B0271 for ; Tue, 19 Nov 2019 05:04:43 -0500 (EST) Received: from smtpin08.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with SMTP id 6CDA12C12 for ; Tue, 19 Nov 2019 10:04:43 +0000 (UTC) X-FDA: 76172592846.08.dolls77_80716660c324b X-HE-Tag: dolls77_80716660c324b X-Filterd-Recvd-Size: 4889 Received: from out30-43.freemail.mail.aliyun.com (out30-43.freemail.mail.aliyun.com [115.124.30.43]) by imf08.hostedemail.com (Postfix) with ESMTP for ; Tue, 19 Nov 2019 10:04:42 +0000 (UTC) X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R191e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04395;MF=alex.shi@linux.alibaba.com;NM=1;PH=DS;RN=38;SR=0;TI=SMTPD_---0TiY4-eE_1574157875; Received: from IT-FVFX43SYHV2H.local(mailfrom:alex.shi@linux.alibaba.com fp:SMTPD_---0TiY4-eE_1574157875) by smtp.aliyun-inc.com(127.0.0.1); Tue, 19 Nov 2019 18:04:36 +0800 Subject: Re: [PATCH v3 3/7] mm/lru: replace pgdat lru_lock with lruvec lock To: Johannes Weiner Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, mgorman@techsingularity.net, tj@kernel.org, hughd@google.com, khlebnikov@yandex-team.ru, daniel.m.jordan@oracle.com, yang.shi@linux.alibaba.com, willy@infradead.org, Michal Hocko , Vladimir Davydov , Roman Gushchin , Shakeel Butt , Chris Down , Thomas Gleixner , Vlastimil Babka , Qian Cai , Andrey Ryabinin , "Kirill A. Shutemov" , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Andrea Arcangeli , David Rientjes , "Aneesh Kumar K.V" , swkhack , "Potyra, Stefan" , Mike Rapoport , Stephen Rothwell , Colin Ian King , Jason Gunthorpe , Mauro Carvalho Chehab , Peng Fan , Nikolay Borisov , Ira Weiny , Kirill Tkhai , Yafang Shao References: <1573874106-23802-1-git-send-email-alex.shi@linux.alibaba.com> <1573874106-23802-4-git-send-email-alex.shi@linux.alibaba.com> <20191118161126.GB365174@cmpxchg.org> From: Alex Shi Message-ID: <85702d50-daf0-ece8-9a5d-e4b860ef2f99@linux.alibaba.com> Date: Tue, 19 Nov 2019 18:04:35 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:60.0) Gecko/20100101 Thunderbird/60.9.1 MIME-Version: 1.0 In-Reply-To: <20191118161126.GB365174@cmpxchg.org> 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: =D4=DA 2019/11/19 =C9=CF=CE=E712:11, Johannes Weiner =D0=B4=B5=C0: > On Sat, Nov 16, 2019 at 11:15:02AM +0800, Alex Shi wrote: >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >> index 62470325f9bc..cf274739e619 100644 >> --- a/mm/memcontrol.c >> +++ b/mm/memcontrol.c >> @@ -1246,6 +1246,42 @@ struct lruvec *mem_cgroup_page_lruvec(struct pa= ge *page, struct pglist_data *pgd >> return lruvec; >> } >> =20 >> +struct lruvec *lock_page_lruvec_irq(struct page *page, >> + struct pglist_data *pgdat) >> +{ >> + struct lruvec *lruvec; >> + >> +again: >> + lruvec =3D mem_cgroup_page_lruvec(page, pgdat); >> + spin_lock_irq(&lruvec->lru_lock); >=20 > This isn't safe. Nothing prevents the page from being moved to a > different memcg in between these two operations, and the lruvec having > been freed by the time you try to acquire the spinlock. >=20 > You need to use the rcu lock to dereference page->mem_cgroup and its > lruvec when coming from the page like this. Hi Johannes, Yes, you are right. Thank a lot to point out this! Could we use rcu lock to guard the lruvec till lruvec->lru_lock getten? +struct lruvec *lock_page_lruvec_irq(struct page *page, + struct pglist_data *pgdat) +{ + struct lruvec *lruvec; + +again: + rcu_read_lock(); + lruvec =3D mem_cgroup_page_lruvec(page, pgdat); + spin_lock_irq(&lruvec->lru_lock); + rcu_read_unlock(); + + /* lruvec may changed in commit_charge() */ + if (lruvec !=3D mem_cgroup_page_lruvec(page, pgdat)) { + spin_unlock_irq(&lruvec->lru_lock); + goto again; + } + + return lruvec; +} >=20 > You also need to use page_memcg_rcu() to insert the appropriate > lockless access barriers, which mem_cgroup_page_lruvec() does not do > since it's designed for use with pgdat->lru_lock. >=20 Since the page_memcg_rcu can not know it under a spin_lock, guess the fol= lowing enhance is fine: @@ -1225,7 +1224,7 @@ struct lruvec *mem_cgroup_page_lruvec(struct page *= page, struct pglist_data *pgd goto out; } - memcg =3D page->mem_cgroup; + memcg =3D READ_ONCE(page->mem_cgroup); /* Millions thanks! Alex