linux-mm.kvack.org archive mirror
 help / color / mirror / Atom feed
From: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
To: Yang Shi <yang.shi@linux.alibaba.com>,
	mhocko@suse.com, david@redhat.com, akpm@linux-foundation.org
Cc: mtk.manpages@gmail.com, linux-man@vger.kernel.org,
	linux-api@vger.kernel.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org
Subject: Re: [v3 PATCH] move_pages.2: Returning positive value is a new error case
Date: Thu, 16 Apr 2020 13:35:51 +0200	[thread overview]
Message-ID: <033ce46c-74c6-7e9f-d89c-cd184a891e1c@gmail.com> (raw)
In-Reply-To: <1580757507-120233-1-git-send-email-yang.shi@linux.alibaba.com>

Hello Yang Shi,

On 2/3/20 8:18 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
> 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.

Thanks for the patch. I've applied it.

@Michal: thanks for the Ack.

Cheers,

Michael

> 
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Michael Kerrisk <mtk.manpages@gmail.com>
> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.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,
> 


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/


      parent reply	other threads:[~2020-04-16 11:35 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-03 19:18 [v3 PATCH] move_pages.2: Returning positive value is a new error case Yang Shi
2020-02-10  9:36 ` Michal Hocko
2020-02-20 17:06   ` Yang Shi
2020-03-10 18:24     ` Yang Shi
2020-04-16 11:35 ` Michael Kerrisk (man-pages) [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=033ce46c-74c6-7e9f-d89c-cd184a891e1c@gmail.com \
    --to=mtk.manpages@gmail.com \
    --cc=akpm@linux-foundation.org \
    --cc=david@redhat.com \
    --cc=linux-api@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-man@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=mhocko@suse.com \
    --cc=yang.shi@linux.alibaba.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).