From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yang Shi Subject: Re: [v2 PATCH] move_pages.2: Returning positive value is a new error case Date: Thu, 30 Jan 2020 09:27:11 -0800 Message-ID: <6f9642ee-5611-4eea-b904-c09cc02b0b17@linux.alibaba.com> References: <1580334531-80354-1-git-send-email-yang.shi@linux.alibaba.com> <20200130120253.GU24244@dhcp22.suse.cz> <20200130134835.GW24244@dhcp22.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20200130134835.GW24244-2MMpYkNvuYDjFM9bn6wA6Q@public.gmane.org> Content-Language: en-US Sender: linux-man-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Michal Hocko , Vlastimil Babka Cc: 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 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"?