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 AF627C33CAA for ; Thu, 23 Jan 2020 03:57:01 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 7E86321835 for ; Thu, 23 Jan 2020 03:57:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7E86321835 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 F2AA66B0003; Wed, 22 Jan 2020 22:57:00 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id EB48F6B0005; Wed, 22 Jan 2020 22:57:00 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DC9666B0006; Wed, 22 Jan 2020 22:57:00 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0065.hostedemail.com [216.40.44.65]) by kanga.kvack.org (Postfix) with ESMTP id C40696B0003 for ; Wed, 22 Jan 2020 22:57:00 -0500 (EST) Received: from smtpin16.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with SMTP id 58369181AEF15 for ; Thu, 23 Jan 2020 03:57:00 +0000 (UTC) X-FDA: 76407538200.16.grip16_7732d92d32e44 X-HE-Tag: grip16_7732d92d32e44 X-Filterd-Recvd-Size: 5559 Received: from out30-132.freemail.mail.aliyun.com (out30-132.freemail.mail.aliyun.com [115.124.30.132]) by imf19.hostedemail.com (Postfix) with ESMTP for ; Thu, 23 Jan 2020 03:56:58 +0000 (UTC) X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R121e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04394;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0ToNc5uW_1579751811; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0ToNc5uW_1579751811) by smtp.aliyun-inc.com(127.0.0.1); Thu, 23 Jan 2020 11:56:54 +0800 Subject: Re: [v2 PATCH] mm: move_pages: report the number of non-attempted pages To: Wei Yang Cc: mhocko@suse.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <1579736331-85494-1-git-send-email-yang.shi@linux.alibaba.com> <20200123032736.GA22196@richard> From: Yang Shi Message-ID: <01fc1c6b-1cab-7f7e-7879-4fc7b0e4a231@linux.alibaba.com> Date: Wed, 22 Jan 2020 19:56:50 -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: <20200123032736.GA22196@richard> 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 1/22/20 7:27 PM, Wei Yang wrote: > On Thu, Jan 23, 2020 at 07:38:51AM +0800, Yang Shi wrote: >> Since commit a49bd4d71637 ("mm, numa: rework do_pages_move"), >> the semantic of move_pages() was changed to return the number of >> non-migrated pages (failed to migration) and the call would be aborted >> immediately if migrate_pages() returns positive value. But it didn't >> report the number of pages that we even haven't attempted to migrate. >> So, fix it by including non-attempted pages in the return value. >> > First, we want to change the semantic of move_pages(2). The return value > indicates the number of pages we didn't managed to migrate? This is my understanding. > > Second, the return value from migrate_pages() doesn't mean the number of pages > we failed to migrate. For example, one -ENOMEM is returned on the first page, > migrate_pages() would return 1. But actually, no page successfully migrated. This would not happen at all since migrate_pages() would just return -ENOMEM instead of a positive value, right? > > Third, even the migrate_pages() return the exact non-migrate page, we are not > sure those non-migrated pages are at the tail of the list. Because in the last > case in migrate_pages(), it just remove the page from list. It could be a page > in the middle of the list. Then, in userspace, how the return value be > leveraged to determine the valid status? Any page in the list could be the > victim. I think this problem has been discussed in another thread. Yes, the status may have non-valid value, but it is supposed to have valid value iff move_pages() return 0. Positive value is an error case, so the validity of status is not guaranteed. > > Sounds we need to think about this carefully. > >> Fixes: a49bd4d71637 ("mm, numa: rework do_pages_move") >> Suggested-by: Michal Hocko >> Cc: Wei Yang >> Cc: [4.17+] >> Signed-off-by: Yang Shi >> --- >> v2: Rebased on top of the latest mainline kernel per Andrew >> >> mm/migrate.c | 24 ++++++++++++++++++++++-- >> 1 file changed, 22 insertions(+), 2 deletions(-) >> >> diff --git a/mm/migrate.c b/mm/migrate.c >> index 86873b6..9b8eb5d 100644 >> --- a/mm/migrate.c >> +++ b/mm/migrate.c >> @@ -1627,8 +1627,18 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes, >> start = i; >> } else if (node != current_node) { >> err = do_move_pages_to_node(mm, &pagelist, current_node); >> - if (err) >> + if (err) { >> + /* >> + * Positive err means the number of failed >> + * pages to migrate. Since we are going to >> + * abort and return the number of non-migrated >> + * pages, so need incude the rest of the >> + * nr_pages that have not attempted as well. >> + */ >> + if (err > 0) >> + err += nr_pages - i - 1; >> goto out; >> + } >> err = store_status(status, start, current_node, i - start); >> if (err) >> goto out; >> @@ -1659,8 +1669,11 @@ 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) { >> + if (err > 0) >> + err += nr_pages - i - 1; >> goto out; >> + } >> if (i > start) { >> err = store_status(status, start, current_node, i - start); >> if (err) >> @@ -1674,6 +1687,13 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes, >> >> /* Make sure we do not overwrite the existing error */ >> err1 = do_move_pages_to_node(mm, &pagelist, current_node); >> + /* >> + * Don't have to report non-attempted pages here since: >> + * - If the above loop is done gracefully there is not non-attempted >> + * page. >> + * - If the above loop is aborted to it means more fatal error >> + * happened, should return err. >> + */ >> if (!err1) >> err1 = store_status(status, start, current_node, i - start); >> if (!err) >> -- >> 1.8.3.1