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,URIBL_BLOCKED,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 08929C33CB7 for ; Wed, 29 Jan 2020 19:05:23 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id BC8A420716 for ; Wed, 29 Jan 2020 19:05:22 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BC8A420716 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 6BAB16B0287; Wed, 29 Jan 2020 14:05:22 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 669746B0288; Wed, 29 Jan 2020 14:05:22 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5A7646B0289; Wed, 29 Jan 2020 14:05:22 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0073.hostedemail.com [216.40.44.73]) by kanga.kvack.org (Postfix) with ESMTP id 424216B0287 for ; Wed, 29 Jan 2020 14:05:22 -0500 (EST) Received: from smtpin30.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id F06072C68 for ; Wed, 29 Jan 2020 19:05:21 +0000 (UTC) X-FDA: 76431600042.30.coach07_68ed8e6fbdb3a X-HE-Tag: coach07_68ed8e6fbdb3a X-Filterd-Recvd-Size: 4360 Received: from out30-132.freemail.mail.aliyun.com (out30-132.freemail.mail.aliyun.com [115.124.30.132]) by imf24.hostedemail.com (Postfix) with ESMTP for ; Wed, 29 Jan 2020 19:05:20 +0000 (UTC) X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R981e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01f04396;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0TojqI9z_1580324714; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0TojqI9z_1580324714) by smtp.aliyun-inc.com(127.0.0.1); Thu, 30 Jan 2020 03:05:17 +0800 Subject: Re: [PATCH] move_pages.2: Returning positive value is a new error case To: Michal Hocko Cc: mtk.manpages@gmail.com, akpm@linux-foundation.org, linux-man@vger.kernel.org, linux-api@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1580322632-93332-1-git-send-email-yang.shi@linux.alibaba.com> <20200129185842.GP24244@dhcp22.suse.cz> From: Yang Shi Message-ID: <0db6a002-d067-8acd-65ee-8c87a32ff769@linux.alibaba.com> Date: Wed, 29 Jan 2020 11:05:11 -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: <20200129185842.GP24244@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 1/29/20 10:58 AM, Michal Hocko wrote: > On Thu 30-01-20 02:30:32, Yang Shi wrote: >> Since commit a49bd4d71637 ("mm, numa: rework do_pages_move"), >> the semantic of move_pages() has changed to return the number of >> non-migrated pages if they were result of a non-fatal reasons (usually a >> busy page). This was an unintentional change that hasn't been noticed >> except for LTP tests which checked for the documented behavior. >> >> There are two ways to go around this change. We can even get back to the >> original behavior and return -EAGAIN whenever migrate_pages is not able >> to migrate pages due to non-fatal reasons. Another option would be to >> simply continue with the changed semantic and extend move_pages >> documentation to clarify that -errno is returned on an invalid input or >> when migration simply cannot succeed (e.g. -ENOMEM, -EBUSY) or the >> number of pages that couldn't have been migrated due to ephemeral >> reasons (e.g. page is pinned or locked for other reasons). >> >> We decided to keep the second option in kernel because this behavior is in >> place for some time without anybody complaining and possibly new users >> depending on it. Also it allows to have a slightly easier error handling >> as the caller knows that it is worth to retry when err > 0. >> >> Update man pages to reflect the new semantic. > Thanks a lot! Looks good to me. I would just add a note that it is > generally recommended to pre-initialize status array by -1 to have a > reliable way to check which pages have been migrated. The man page says > "The array contains valid values only if move_pages() did not return an > error." > > I would just add. "Pre initialization of the array to -1 or similar > value which cannot represent a real numa node could help to identify > pages that have been migrated". Sure. Adding this note right after the explanation of positive value error seems fine? > >> Cc: Michal Hocko >> Cc: Michael Kerrisk >> Signed-off-by: Yang Shi > Acked-by: Michal Hocko > >> --- >> man2/move_pages.2 | 6 +++++- >> 1 file changed, 5 insertions(+), 1 deletion(-) >> >> diff --git a/man2/move_pages.2 b/man2/move_pages.2 >> index 1bf1053..c6cf3f8 100644 >> --- a/man2/move_pages.2 >> +++ b/man2/move_pages.2 >> @@ -164,9 +164,13 @@ returns zero. >> .\" do the right thing? >> On error, it returns \-1, and sets >> .I errno >> -to indicate the error. >> +to indicate the error. Or positive value to report the number of >> +non-migrated pages. >> .SH ERRORS >> .TP >> +.B Positive value >> +The number of non-migrated pages if they were result of a non-fatal >> +reasons since version 4.17. >> .B E2BIG >> Too many pages to move. >> Since Linux 2.6.29, >> -- >> 1.8.3.1