From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Hildenbrand Subject: Re: [PATCH] move_pages.2: Returning positive value is a new error case Date: Fri, 31 Jan 2020 11:49:19 +0100 Message-ID: <9aac5bff-3a18-ec5f-5aa0-82c38d367590@redhat.com> References: <1580322632-93332-1-git-send-email-yang.shi@linux.alibaba.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1580322632-93332-1-git-send-email-yang.shi@linux.alibaba.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Yang Shi , mhocko@suse.com, mtk.manpages@gmail.com, akpm@linux-foundation.org Cc: 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 29.01.20 19:30, 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 > 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. "If a positive value is returned, it's 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. s/result/the result/ ? s/a reasons/reasons/ ? s/since version 4.17/(since 4.17)/ ? > .B E2BIG > Too many pages to move. > Since Linux 2.6.29, > -- Thanks, David / dhildenb