linux-kernel - Re: [v3 PATCH] move_pages.2: Returning positive value is a new error case

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Date:   Tue, 10 Mar 2020 11:24:21 -0700
From:   Yang Shi <shy828301@...il.com>
To:     mtk.manpages@...il.com
Cc:     Yang Shi <yang.shi@...ux.alibaba.com>,
        Michal Hocko <mhocko@...nel.org>, david@...hat.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-man@...r.kernel.org, linux-api@...r.kernel.org,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [v3 PATCH] move_pages.2: Returning positive value is a new error case

On Thu, Feb 20, 2020 at 9:07 AM Yang Shi <yang.shi@...ux.alibaba.com> wrote:
>
>
>
> On 2/10/20 1:36 AM, Michal Hocko wrote:
> > On Tue 04-02-20 03:18:27, 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 <mhocko@...e.com>
> >> Cc: Michael Kerrisk <mtk.manpages@...il.com>
> >> Signed-off-by: Yang Shi <yang.shi@...ux.alibaba.com>
>

Hi Michale,

Maybe my work email went to your spam folder. So, ping with my
personal email. Would you please consider take this patch?

Thanks,
Yang

> Hi Michael,
>
> Would you please consider take this patch? The kernel change has been
> upstreamed.
>
> Thanks,
> Yang
>
> > Acked-by: Michal Hocko <mhocko@...e.com>
> >
> >> ---
> >> v3: * Fixed the comments from David Hildenbrand.
> >>      * Fixed the inaccuracy about pre-initialized status array values.
> >> v2: * Added notes about status array per Michal.
> >>      * Added Michal's Acked-by.
> >>
> >>   man2/move_pages.2 | 10 ++++++++--
> >>   1 file changed, 8 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/man2/move_pages.2 b/man2/move_pages.2
> >> index 1bf1053..50c83a4 100644
> >> --- a/man2/move_pages.2
> >> +++ b/man2/move_pages.2
> >> @@ -104,7 +104,9 @@ pages that need to be moved.
> >>   is an array of integers that return the status of each page.
> >>   The array contains valid values only if
> >>   .BR move_pages ()
> >> -did not return an error.
> >> +did not return an error.  Pre-initialization of the array to the value
> >> +which cannot represent a real numa node or valid error of status array
> >> +could help to identify pages that have been migrated
> >>   .PP
> >>   .I flags
> >>   specify what types of pages to move.
> >> @@ -164,9 +166,13 @@ returns zero.
> >>   .\" do the right thing?
> >>   On error, it returns \-1, and sets
> >>   .I errno
> >> -to indicate the error.
> >> +to indicate the error. If positive value is returned, it is the number of
> >> +non-migrated pages.
> >>   .SH ERRORS
> >>   .TP
> >> +.B Positive value
> >> +The number of non-migrated pages if they were the result of non-fatal
> >> +reasons (since version 4.17).
> >>   .B E2BIG
> >>   Too many pages to move.
> >>   Since Linux 2.6.29,
> >> --
> >> 1.8.3.1
>