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=-8.3 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 45C20C11D13 for ; Thu, 20 Feb 2020 17:06:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 24D7220722 for ; Thu, 20 Feb 2020 17:06:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728555AbgBTRGN (ORCPT ); Thu, 20 Feb 2020 12:06:13 -0500 Received: from out30-57.freemail.mail.aliyun.com ([115.124.30.57]:59432 "EHLO out30-57.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727915AbgBTRGM (ORCPT ); Thu, 20 Feb 2020 12:06:12 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R101e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01f04428;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0TqSIWZ0_1582218362; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0TqSIWZ0_1582218362) by smtp.aliyun-inc.com(127.0.0.1); Fri, 21 Feb 2020 01:06:05 +0800 Subject: Re: [v3 PATCH] move_pages.2: Returning positive value is a new error case To: mtk.manpages@gmail.com Cc: Michal Hocko , david@redhat.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: <1580757507-120233-1-git-send-email-yang.shi@linux.alibaba.com> <20200210093635.GC10636@dhcp22.suse.cz> From: Yang Shi Message-ID: <92f30e24-7b77-b21a-ed3a-efc55bc500c6@linux.alibaba.com> Date: Thu, 20 Feb 2020 09:06:00 -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: <20200210093635.GC10636@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/10/20 1:36 AM, Michal Hocko wrote: > On Tue 04-02-20 03:18:27, 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. >> >> Cc: Michal Hocko >> Cc: Michael Kerrisk >> Signed-off-by: Yang Shi Hi Michael, Would you please consider take this patch? The kernel change has been upstreamed. Thanks, Yang > Acked-by: Michal Hocko > >> --- >> v3: * Fixed the comments from David Hildenbrand. >> * Fixed the inaccuracy about pre-initialized status array values. >> v2: * Added notes about status array per Michal. >> * Added Michal's Acked-by. >> >> man2/move_pages.2 | 10 ++++++++-- >> 1 file changed, 8 insertions(+), 2 deletions(-) >> >> diff --git a/man2/move_pages.2 b/man2/move_pages.2 >> index 1bf1053..50c83a4 100644 >> --- a/man2/move_pages.2 >> +++ b/man2/move_pages.2 >> @@ -104,7 +104,9 @@ pages that need to be moved. >> is an array of integers that return the status of each page. >> The array contains valid values only if >> .BR move_pages () >> -did not return an error. >> +did not return an error. Pre-initialization of the array to the value >> +which cannot represent a real numa node or valid error of status array >> +could help to identify pages that have been migrated >> .PP >> .I flags >> specify what types of pages to move. >> @@ -164,9 +166,13 @@ returns zero. >> .\" do the right thing? >> On error, it returns \-1, and sets >> .I errno >> -to indicate the error. >> +to indicate the error. If positive value is returned, it is the number of >> +non-migrated pages. >> .SH ERRORS >> .TP >> +.B Positive value >> +The number of non-migrated pages if they were the result of non-fatal >> +reasons (since version 4.17). >> .B E2BIG >> Too many pages to move. >> Since Linux 2.6.29, >> -- >> 1.8.3.1