From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: [v2 PATCH] move_pages.2: Returning positive value is a new error case Date: Thu, 30 Jan 2020 14:48:35 +0100 Message-ID: <20200130134835.GW24244@dhcp22.suse.cz> References: <1580334531-80354-1-git-send-email-yang.shi@linux.alibaba.com> <20200130120253.GU24244@dhcp22.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Vlastimil Babka Cc: Yang Shi , 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 List-Id: linux-api@vger.kernel.org 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. -- Michal Hocko SUSE Labs