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=-9.7 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_GIT autolearn=ham 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 9A651C33CB7 for ; Wed, 29 Jan 2020 18:30:47 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id CFAC820732 for ; Wed, 29 Jan 2020 18:30:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CFAC820732 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 4B1506B027B; Wed, 29 Jan 2020 13:30:46 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 461696B027C; Wed, 29 Jan 2020 13:30:46 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 34FCC6B027D; Wed, 29 Jan 2020 13:30:46 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0078.hostedemail.com [216.40.44.78]) by kanga.kvack.org (Postfix) with ESMTP id 1CAA16B027B for ; Wed, 29 Jan 2020 13:30:46 -0500 (EST) Received: from smtpin16.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id D167D499605 for ; Wed, 29 Jan 2020 18:30:45 +0000 (UTC) X-FDA: 76431512850.16.shade19_5dd49d9c3fc23 X-HE-Tag: shade19_5dd49d9c3fc23 X-Filterd-Recvd-Size: 3123 Received: from out30-44.freemail.mail.aliyun.com (out30-44.freemail.mail.aliyun.com [115.124.30.44]) by imf21.hostedemail.com (Postfix) with ESMTP for ; Wed, 29 Jan 2020 18:30:44 +0000 (UTC) X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R301e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01f04455;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0TojljaH_1580322632; Received: from localhost(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0TojljaH_1580322632) by smtp.aliyun-inc.com(127.0.0.1); Thu, 30 Jan 2020 02:30:40 +0800 From: Yang Shi To: mhocko@suse.com, mtk.manpages@gmail.com, akpm@linux-foundation.org Cc: yang.shi@linux.alibaba.com, linux-man@vger.kernel.org, linux-api@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH] move_pages.2: Returning positive value is a new error case Date: Thu, 30 Jan 2020 02:30:32 +0800 Message-Id: <1580322632-93332-1-git-send-email-yang.shi@linux.alibaba.com> X-Mailer: git-send-email 1.8.3.1 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: 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 --- 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