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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,USER_AGENT_SANE_1 autolearn=no 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 78269C432C3 for ; Wed, 20 Nov 2019 11:41:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5879221906 for ; Wed, 20 Nov 2019 11:41:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729351AbfKTLlz (ORCPT ); Wed, 20 Nov 2019 06:41:55 -0500 Received: from out30-131.freemail.mail.aliyun.com ([115.124.30.131]:41038 "EHLO out30-131.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728495AbfKTLlz (ORCPT ); Wed, 20 Nov 2019 06:41:55 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R861e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04394;MF=alex.shi@linux.alibaba.com;NM=1;PH=DS;RN=38;SR=0;TI=SMTPD_---0TidwO.r_1574250104; Received: from IT-FVFX43SYHV2H.local(mailfrom:alex.shi@linux.alibaba.com fp:SMTPD_---0TidwO.r_1574250104) by smtp.aliyun-inc.com(127.0.0.1); Wed, 20 Nov 2019 19:41:45 +0800 Subject: Re: [PATCH v4 3/9] 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, shakeelb@google.com, Michal Hocko , Vladimir Davydov , Roman Gushchin , 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: <1574166203-151975-1-git-send-email-alex.shi@linux.alibaba.com> <1574166203-151975-4-git-send-email-alex.shi@linux.alibaba.com> <20191119160456.GD382712@cmpxchg.org> From: Alex Shi Message-ID: Date: Wed, 20 Nov 2019 19:41:44 +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: <20191119160456.GD382712@cmpxchg.org> Content-Type: text/plain; charset=gbk Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ÔÚ 2019/11/20 ÉÏÎç12:04, Johannes Weiner дµÀ: >> + >> + return lruvec; > While this works in practice, it looks wrong because it doesn't follow > the mem_cgroup_page_lruvec() rules. > > Please open-code spin_lock_irq(&pgdat->__lruvec->lru_lock) instead. > That's right. Thanks for suggestion! >> @@ -1246,6 +1245,46 @@ struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct pglist_data *pgd >> return lruvec; >> } >> >> +struct lruvec *lock_page_lruvec_irq(struct page *page, >> + struct pglist_data *pgdat) >> +{ >> + struct lruvec *lruvec; >> + >> +again: >> + rcu_read_lock(); >> + lruvec = mem_cgroup_page_lruvec(page, pgdat); >> + spin_lock_irq(&lruvec->lru_lock); >> + rcu_read_unlock(); > The spinlock doesn't prevent the lruvec from being freed > > You deleted the rules from the mem_cgroup_page_lruvec() documentation, > but they still apply: if the page is already !PageLRU() by the time > you get here, it could get reclaimed or migrated to another cgroup, > and that can free the memcg/lruvec. Merely having the lru_lock held > does not prevent this. Forgive my idiot, I still don't know the details of unsafe lruvec here. >From my shortsight, the spin_lock_irq(embedded a preempt_disable) could block all rcu syncing thus, keep all memcg alive until the preempt_enabled in unspinlock, is this right? If so even the page->mem_cgroup is migrated to others cgroups, the new and old cgroup should still be alive here. > > Either the page needs to be locked, or the page needs to be PageLRU > with the lru_lock held to prevent somebody else from isolating > it. Otherwise, the lruvec is not safe to use. Do you mean that we may get the wrong lruvec->lru_lock if !PageLRU, so, the page may got freed by others? Sorry I got last there. Thanks Alex