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=-2.5 required=3.0 tests=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 BDA4ACA9EC5 for ; Wed, 30 Oct 2019 17:45:38 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 60A54205ED for ; Wed, 30 Oct 2019 17:45:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 60A54205ED Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 0E0666B0007; Wed, 30 Oct 2019 13:45:38 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 091416B0008; Wed, 30 Oct 2019 13:45:38 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id EE8786B000A; Wed, 30 Oct 2019 13:45:37 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0115.hostedemail.com [216.40.44.115]) by kanga.kvack.org (Postfix) with ESMTP id CC67D6B0007 for ; Wed, 30 Oct 2019 13:45:37 -0400 (EDT) Received: from smtpin09.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with SMTP id 65C07180BD9CC for ; Wed, 30 Oct 2019 17:45:37 +0000 (UTC) X-FDA: 76101178314.09.screw05_4e0f776beb233 X-HE-Tag: screw05_4e0f776beb233 X-Filterd-Recvd-Size: 3197 Received: from mx1.suse.de (mx2.suse.de [195.135.220.15]) by imf32.hostedemail.com (Postfix) with ESMTP for ; Wed, 30 Oct 2019 17:45:36 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 02464ACD9; Wed, 30 Oct 2019 17:45:34 +0000 (UTC) Date: Wed, 30 Oct 2019 18:45:33 +0100 From: Michal Hocko To: Minchan Kim Cc: zhong jiang , akpm@linux-foundation.org, hannes@cmpxchg.org, ktkhai@virtuozzo.com, linux-mm@kvack.org Subject: Re: [PATCH] mm: fix unevictable page reclaim when calling madvise_pageout Message-ID: <20191030174533.GL31513@dhcp22.suse.cz> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191030165239.GA167773@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) 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 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? -- Michal Hocko SUSE Labs