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 95B68C2D0DB for ; Mon, 20 Jan 2020 13:00:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 72E8A24125 for ; Mon, 20 Jan 2020 13:00:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727289AbgATNAG (ORCPT ); Mon, 20 Jan 2020 08:00:06 -0500 Received: from out30-56.freemail.mail.aliyun.com ([115.124.30.56]:48280 "EHLO out30-56.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726619AbgATNAF (ORCPT ); Mon, 20 Jan 2020 08:00:05 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R171e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e07417;MF=alex.shi@linux.alibaba.com;NM=1;PH=DS;RN=38;SR=0;TI=SMTPD_---0ToETcqo_1579525195; Received: from IT-FVFX43SYHV2H.local(mailfrom:alex.shi@linux.alibaba.com fp:SMTPD_---0ToETcqo_1579525195) by smtp.aliyun-inc.com(127.0.0.1); Mon, 20 Jan 2020 20:59:57 +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: <9ee80b68-a78f-714a-c727-1f6d2b4f87ea@linux.alibaba.com> Date: Mon, 20 Jan 2020 20:58:09 +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: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ÔÚ 2020/1/17 ÉÏÎç5:52, Johannes Weiner дµÀ: > You simply cannot serialize on page->mem_cgroup->lruvec when > page->mem_cgroup isn't stable. You need to serialize on the page > itself, one way or another, to make this work. > > > 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? > Hi Johannes, I am trying to figure out the solution of atomic PageLRU, but is blocked by the following sitations, when PageLRU and lru list was protected together under lru_lock, the PageLRU could be a indicator if page on lru list But now seems it can't be the indicator anymore. Could you give more clues of stabilization usage of PageLRU? __page_cache_release/release_pages/compaction __pagevec_lru_add if (TestClearPageLRU(page)) if (!PageLRU()) lruvec_lock(); list_add(); lruvec_unlock(); SetPageLRU() //position 1 lock_page_lruvec_irqsave(page, &flags); del_page_from_lru_list(page, lruvec, ..); unlock_page_lruvec_irqrestore(lruvec, flags); SetPageLRU() //position 2 Thanks a lot! 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? >