From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vlastimil Babka Subject: Re: [v2 PATCH] move_pages.2: Returning positive value is a new error case Date: Thu, 30 Jan 2020 13:56:20 +0100 Message-ID: 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=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20200130120253.GU24244-2MMpYkNvuYDjFM9bn6wA6Q@public.gmane.org> Content-Language: en-US Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Michal Hocko Cc: Yang Shi , mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org, linux-man-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-api@vger.kernel.org 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?