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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,USER_AGENT_SANE_1 autolearn=no 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 A75C5C35240 for ; Thu, 30 Jan 2020 17:27:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8002F2083E for ; Thu, 30 Jan 2020 17:27:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727487AbgA3R1T (ORCPT ); Thu, 30 Jan 2020 12:27:19 -0500 Received: from out30-54.freemail.mail.aliyun.com ([115.124.30.54]:47826 "EHLO out30-54.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726514AbgA3R1T (ORCPT ); Thu, 30 Jan 2020 12:27:19 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R651e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04407;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0TonDCBV_1580405233; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0TonDCBV_1580405233) by smtp.aliyun-inc.com(127.0.0.1); Fri, 31 Jan 2020 01:27:16 +0800 Subject: Re: [v2 PATCH] move_pages.2: Returning positive value is a new error case To: Michal Hocko , Vlastimil Babka 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: <1580334531-80354-1-git-send-email-yang.shi@linux.alibaba.com> <20200130120253.GU24244@dhcp22.suse.cz> <20200130134835.GW24244@dhcp22.suse.cz> From: Yang Shi Message-ID: <6f9642ee-5611-4eea-b904-c09cc02b0b17@linux.alibaba.com> Date: Thu, 30 Jan 2020 09:27:11 -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: <20200130134835.GW24244@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 1/30/20 5:48 AM, Michal Hocko wrote: > On Thu 30-01-20 13:56:20, Vlastimil Babka wrote: >> On 1/30/20 1:02 PM, Michal Hocko wrote: >>> On Thu 30-01-20 10:06:28, Vlastimil Babka wrote: >>>> On 1/29/20 10:48 PM, 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 >>>> The manpage says EBUSY, not EAGAIN? And should its description be >>>> updated too? >>> The idea was that we _could_ return EAGAIN from the syscall if >>> migrate_pages > 0. >>> >>>> I.e. that it's no longer returned since 4.17? >>> I am pretty sure this will require a deeper consideration. Do we return >>> EIO/EINVAL? >> I thought the manpage says we return -EBUSY, but I misread it, this part >> was not about errno, but the status array. So there's nothing to update >> there, sorry about the noise. >> >> BTW, the suggestion to "Pre-initialization of the array to -1" means >> effectively it's pre-initialized to -EPERM. That's fine now as -EPERM is >> not one of the codes listed as possible to be returned via the array, >> but perhaps it's not entirely future-proof? > Hmm, I didn't realize EPERM is refering to 1. The wording however > suggests also any other value that cannot represent a valid NUMA node. > So maybe we should just drop the node about -1. Or maybe we just say "any value which doesn't represent a valid NUMA node or valid error of status array"?