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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 90DD8CA9EC3 for ; Thu, 31 Oct 2019 09:46:55 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 59A5E2086D for ; Thu, 31 Oct 2019 09:46:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 59A5E2086D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=huawei.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id E10136B000A; Thu, 31 Oct 2019 05:46:54 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id DC0C16B000D; Thu, 31 Oct 2019 05:46:54 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CD67A6B026B; Thu, 31 Oct 2019 05:46:54 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0228.hostedemail.com [216.40.44.228]) by kanga.kvack.org (Postfix) with ESMTP id A7FC66B000A for ; Thu, 31 Oct 2019 05:46:54 -0400 (EDT) Received: from smtpin02.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with SMTP id 147BE8249980 for ; Thu, 31 Oct 2019 09:46:54 +0000 (UTC) X-FDA: 76103600748.02.form05_1ed62e4d23a0d X-HE-Tag: form05_1ed62e4d23a0d X-Filterd-Recvd-Size: 4641 Received: from huawei.com (szxga06-in.huawei.com [45.249.212.32]) by imf18.hostedemail.com (Postfix) with ESMTP for ; Thu, 31 Oct 2019 09:46:51 +0000 (UTC) Received: from DGGEMS401-HUB.china.huawei.com (unknown [172.30.72.60]) by Forcepoint Email with ESMTP id CA9E1504FE535DF675D5; Thu, 31 Oct 2019 17:46:46 +0800 (CST) Received: from [127.0.0.1] (10.133.219.218) by DGGEMS401-HUB.china.huawei.com (10.3.19.201) with Microsoft SMTP Server id 14.3.439.0; Thu, 31 Oct 2019 17:46:44 +0800 Message-ID: <5DBAAD83.8050800@huawei.com> Date: Thu, 31 Oct 2019 17:46:43 +0800 From: zhong jiang User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:12.0) Gecko/20120428 Thunderbird/12.0.1 MIME-Version: 1.0 To: Johannes Weiner CC: Michal Hocko , Minchan Kim , , , Subject: Re: [PATCH] mm: fix unevictable page reclaim when calling madvise_pageout References: <1572275317-63910-1-git-send-email-zhongjiang@huawei.com> <20191029081102.GB31513@dhcp22.suse.cz> <5DB806D1.8020503@huawei.com> <20191029094039.GH31513@dhcp22.suse.cz> <5DB81838.6020208@huawei.com> <20191030165239.GA167773@google.com> <20191030174533.GL31513@dhcp22.suse.cz> <20191030193307.GA48128@cmpxchg.org> In-Reply-To: <20191030193307.GA48128@cmpxchg.org> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.133.219.218] X-CFilter-Loop: Reflected 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: On 2019/10/31 3:33, Johannes Weiner wrote: > On Wed, Oct 30, 2019 at 06:45:33PM +0100, Michal Hocko wrote: >> On Wed 30-10-19 09:52:39, Minchan Kim wrote: >>> On Tue, Oct 29, 2019 at 06:45:12PM +0800, zhong jiang wrote: >>>> On 2019/10/29 17:40, Michal Hocko wrote: >>>>> On Tue 29-10-19 17:30:57, zhong jiang wrote: >>>>>> On 2019/10/29 16:11, Michal Hocko wrote: >>>>>>> [Cc Minchan] >>>>> [...] >>>>>>> Removing a long existing BUG_ON begs for a much better explanation. >>>>>>> shrink_page_list is not a trivial piece of code but I _suspect_ that >>>>>>> removing it should be ok for mapped pages at least (try_to_unmap) but I >>>>>>> am not so sure how unmapped unevictable pages are handled from top of my >>>>>>> head. >>>>>> As to the unmapped unevictable pages. shrink_page_list has taken that into account. >>>>>> >>>>>> shinkr_page_list >>>>>> page_evictable --> will filter the unevictable pages to putback its lru. >>>>> Ohh, it is right there at the top. Missed it. The check has been added >>>>> by Nick along with the BUG_ON. So it is sounds more like a "this >>>>> shouldn't happen" bugon. I wouldn't mind to remove it with that >>>>> justification. >>>> As you has said, Minchan fix the same kind of bug by checking PageUnevictable (I did not notice before) >>>> Wait for Minchan to see whether he has better reason. thanks, >>> madvise_pageout could work with a shared page and one of the vmas among processes >>> could do mlock so it could pass Unevictable LRU pages into shrink_page_list. >>> It's pointless to try reclaim unevictable pages from the beginning so I want to fix >>> madvise_pageout via introducing only_evictable flag into the API so that >>> madvise_pageout uses it as "true". >>> >>> If we want to remove the PageUnevictable VM_BUG_ON_PAGE in shrink_page_list, >>> I want to see more strong reason why it happens and why caller couldn't >>> filter them out from the beginning. >> Why is this preferable over removing the VM_BUG_ON condition? In other >> words why should we keep PageUnevictable check there? > The mlock LRU shuffling is a bit tricky and can race with page reclaim > or others isolating the page from the LRU list. If another isolator > wins, it has to move the page during putback on behalf of mlock. > > See the implementation and comments in __pagevec_lru_add_fn(). I see that comments in __pagevec_lru_add_fn. I have some confusion. It will result in evictable page strand in an unevictable lru without PageMlocked due to disorder If I understand it correctly. vmscan can see !page_evictable(). It should be PageMLocked is set in evictable list. Is there any race window ? Thanks, zhong jiang > That's why page reclaim can see !page_evictable(), but it must not see > pages that have the PageUnevictable lru bit already set. Because that > would mean the isolation/putback machinery messed up somewhere and the > page LRU state is corrupt. > > As that machinery is non-trivial, it's useful to have that sanity > check in page reclaim. > > . >