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 99A17C33CB1 for ; Sun, 19 Jan 2020 11:33:57 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 38CA520679 for ; Sun, 19 Jan 2020 11:33:57 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 38CA520679 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 9A2B86B0574; Sun, 19 Jan 2020 06:33:56 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 953B56B0575; Sun, 19 Jan 2020 06:33:56 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 868D16B0576; Sun, 19 Jan 2020 06:33:56 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0042.hostedemail.com [216.40.44.42]) by kanga.kvack.org (Postfix) with ESMTP id 6D4576B0574 for ; Sun, 19 Jan 2020 06:33:56 -0500 (EST) Received: from smtpin05.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with SMTP id 0F347180AD811 for ; Sun, 19 Jan 2020 11:33:56 +0000 (UTC) X-FDA: 76394174472.05.top95_5c5e191dc7f47 X-HE-Tag: top95_5c5e191dc7f47 X-Filterd-Recvd-Size: 5428 Received: from out30-133.freemail.mail.aliyun.com (out30-133.freemail.mail.aliyun.com [115.124.30.133]) by imf32.hostedemail.com (Postfix) with ESMTP for ; Sun, 19 Jan 2020 11:33:54 +0000 (UTC) X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R271e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01f04452;MF=alex.shi@linux.alibaba.com;NM=1;PH=DS;RN=38;SR=0;TI=SMTPD_---0To5Mgrg_1579433626; Received: from IT-FVFX43SYHV2H.local(mailfrom:alex.shi@linux.alibaba.com fp:SMTPD_---0To5Mgrg_1579433626) by smtp.aliyun-inc.com(127.0.0.1); Sun, 19 Jan 2020 19:33:48 +0800 Subject: Re: [PATCH v8 03/10] 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: <1579143909-156105-1-git-send-email-alex.shi@linux.alibaba.com> <1579143909-156105-4-git-send-email-alex.shi@linux.alibaba.com> <20200116215222.GA64230@cmpxchg.org> From: Alex Shi Message-ID: <36a55567-a701-ad6c-e4ea-79fd2021a648@linux.alibaba.com> Date: Sun, 19 Jan 2020 19:32:02 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.3.1 MIME-Version: 1.0 In-Reply-To: <20200116215222.GA64230@cmpxchg.org> Content-Type: text/plain; charset=gbk Content-Transfer-Encoding: 7bit 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: > In a previous review, I pointed out the following race condition > between page charging and compaction: > > compaction: generic_file_buffered_read: > > page_cache_alloc() > > !PageBuddy() > > lock_page_lruvec(page) > lruvec = mem_cgroup_page_lruvec() > spin_lock(&lruvec->lru_lock) > if lruvec != mem_cgroup_page_lruvec() > goto again > > add_to_page_cache_lru() > mem_cgroup_commit_charge() > page->mem_cgroup = foo > lru_cache_add() > __pagevec_lru_add() > SetPageLRU() > > if PageLRU(page): > __isolate_lru_page() > > As far as I can see, you have not addressed this. You have added > lock_page_memcg(), but that prevents charged pages from moving between > cgroups, it does not prevent newly allocated pages from being charged. > yes, it's my fault to oversee this problem. ... > > So here is a crazy idea that may be worth exploring: > > Right now, pgdat->lru_lock protects both PageLRU *and* the lruvec's > linked list. > > Can we make PageLRU atomic and use it to stabilize the lru_lock > instead, and then use the lru_lock only serialize list operations? > Sounds a good idea. I will try this. Thanks Alex > I.e. in compaction, you'd do > > if (!TestClearPageLRU(page)) > goto isolate_fail; > /* > * We isolated the page's LRU state and thereby locked out all > * other isolators, including cgroup page moving, page reclaim, > * page freeing etc. That means page->mem_cgroup is now stable > * and we can safely look up the correct lruvec and take the > * page off its physical LRU list. > */ > lruvec = mem_cgroup_page_lruvec(page); > spin_lock_irq(&lruvec->lru_lock); > del_page_from_lru_list(page, lruvec, page_lru(page)); > > Putback would mostly remain the same (although you could take the > PageLRU setting out of the list update locked section, as long as it's > set after the page is physically linked): > > /* LRU isolation pins page->mem_cgroup */ > lruvec = mem_cgroup_page_lruvec(page) > spin_lock_irq(&lruvec->lru_lock); > add_page_to_lru_list(...); > spin_unlock_irq(&lruvec->lru_lock); > > SetPageLRU(page); > > And you'd have to carefully review and rework other sites that rely on > PageLRU: reclaim, __page_cache_release(), __activate_page() etc. > > Especially things like activate_page(), which used to only check > PageLRU to shuffle the page on the LRU list would now have to briefly > clear PageLRU and then set it again afterwards. > > However, aside from a bit more churn in those cases, and the > unfortunate additional atomic operations, I currently can't think of a > fundamental reason why this wouldn't work. > > Hugh, what do you think? >