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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, UNPARSEABLE_RELAY,USER_AGENT_SANE_1 autolearn=unavailable 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 E1108C2D0DB for ; Tue, 21 Jan 2020 19:01:45 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id B10D121734 for ; Tue, 21 Jan 2020 19:01:45 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B10D121734 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 4A0086B0273; Tue, 21 Jan 2020 14:01:45 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 450BC6B0274; Tue, 21 Jan 2020 14:01:45 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3675F6B0275; Tue, 21 Jan 2020 14:01:45 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0072.hostedemail.com [216.40.44.72]) by kanga.kvack.org (Postfix) with ESMTP id 223D36B0273 for ; Tue, 21 Jan 2020 14:01:45 -0500 (EST) Received: from smtpin07.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with SMTP id D12D8181AEF1A for ; Tue, 21 Jan 2020 19:01:44 +0000 (UTC) X-FDA: 76402560528.07.verse74_2c30192b3a136 X-HE-Tag: verse74_2c30192b3a136 X-Filterd-Recvd-Size: 5788 Received: from out30-132.freemail.mail.aliyun.com (out30-132.freemail.mail.aliyun.com [115.124.30.132]) by imf44.hostedemail.com (Postfix) with ESMTP for ; Tue, 21 Jan 2020 19:01:43 +0000 (UTC) X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R881e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01f04397;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0ToInc38_1579633297; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0ToInc38_1579633297) by smtp.aliyun-inc.com(127.0.0.1); Wed, 22 Jan 2020 03:01:40 +0800 Subject: Re: [PATCH] mm: move_pages: fix the return value if there are not-migrated pages To: Michal Hocko , Wei Yang Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <1579325203-16405-1-git-send-email-yang.shi@linux.alibaba.com> <20200120130624.GD18451@dhcp22.suse.cz> <20200120131744.GE18451@dhcp22.suse.cz> <20200121014416.GC1567@richard> <20200121084040.GC29276@dhcp22.suse.cz> From: Yang Shi Message-ID: <27b993f4-cc50-d5a9-1cda-89dd022aea16@linux.alibaba.com> Date: Tue, 21 Jan 2020 11:01:30 -0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20200121084040.GC29276@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US 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 1/21/20 12:40 AM, Michal Hocko wrote: > On Tue 21-01-20 09:44:16, Wei Yang wrote: >> On Mon, Jan 20, 2020 at 02:17:44PM +0100, Michal Hocko wrote: >>> On Mon 20-01-20 14:06:26, Michal Hocko wrote: >>>> On Sat 18-01-20 13:26:43, Yang Shi wrote: >>>>> The do_move_pages_to_node() might return > 0 value, the number of pages >>>>> that are not migrated, then the value will be returned to userspace >>>>> directly. But, move_pages() syscall would just return 0 or errno. So, >>>>> we need reset the return value to 0 for such case as what pre-v4.17 did. >>>> The patch is wrong. migrate_pages returns the number of pages it >>>> _hasn't_ migrated or -errno. Yeah that semantic sucks but... >>>> So err != 0 is always an error. Except err > 0 doesn't really provide >>>> any useful information to the userspace. I cannot really remember what >>>> was the actual behavior before my rework because there were some gotchas >>>> hidden there. >>> OK, so I've double checked. do_move_page_to_node_array would carry the >>> error code over to do_pages_move and it would store the status stored >>> in the pm array. It contains page_to_nid(page) so the resulting code >>> indeed behaves properly before my change and this is a regression. I >> Thanks, I see the change. >> >>> have a very vague recollection that this has been brought up already. >>> <...looks in notes...> >>> Found it! The report is >>> http://lkml.kernel.org/r/0329efa0984b9b0252ef166abb4498c0795fab36.1535113317.git.jstancek@redhat.com >>> and my proposed workaround was http://lkml.kernel.org/r/20180829145537.GZ10223@dhcp22.suse.cz >> Well, the above two links return 404. > You are right. They are not archived for some reason. Anyway, the patch > I was proposing back then is below: > > commit cfb88c266b645197135cde2905c2bfc82f6d82a9 > Author: Michal Hocko > Date: Wed Nov 14 12:19:09 2018 +0100 > > mm: fix do_pages_move error reporting > > a49bd4d71637 ("mm, numa: rework do_pages_move") has changed the way how > we report error to layers above. As the changelog mentioned the semantic > was quite unclear previously because the return 0 could mean both > success and failure. > > The above mentioned commit didn't get all the way down to fix this > completely because it doesn't report pages that we even haven't > attempted to migrate and therefore we cannot simply say that the > semantic is: > - err < 0 - errno > - err >= 0 number of non-migrated pages. > > Fixes: a49bd4d71637 ("mm, numa: rework do_pages_move") > Signed-off-by: Michal Hocko Thanks, Michal. But, it looks this patch still could return > 0 value (the total number of non-migrated pages, including not even attempted pages) too, but the problem we are trying to fix is to make do_pages_move() return <= 0 value only since the man page of move_pages() doesn't allow return > 0 value. And, by looking into the old code (v4.16), I spotted another problem. The migrate_pages() would store the migration failure error code into page_to_node->status. So, When do_move_page_to_node_array() returns > 0 value, the return value would be reset to 0 and the migration error codes for non-migrated pages would be stored into status to return to userspace. But, the rework removed this. I didn't dig into the intention of the rework, is it expected? > > diff --git a/mm/migrate.c b/mm/migrate.c > index f7e4bfdc13b7..aa53ebc523eb 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -1615,8 +1615,16 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes, > goto out_flush; > > err = do_move_pages_to_node(mm, &pagelist, current_node); > - if (err) > + if (err) { > + /* > + * Possitive err means the number of failed pages to > + * migrate. Make sure to report the rest of the > + * nr_pages is not migrated as well. > + */ > + if (err > 0) > + err += nr_pages - i - 1; > goto out; > + } > if (i > start) { > err = store_status(status, start, current_node, i - start); > if (err)