linux-kernel - Re: [PATCH] move_pages.2: not return ENOENT if the page are already on the target nodes

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Message-ID: <20191218101711.GB21485@dhcp22.suse.cz>
Date:   Wed, 18 Dec 2019 11:17:11 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
        Yang Shi <yang.shi@...ux.alibaba.com>, cl@...ux.com,
        cai@....pw, akpm@...ux-foundation.org, linux-man@...r.kernel.org,
        linux-api@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] move_pages.2: not return ENOENT if the page are already
 on the target nodes

On Tue 17-12-19 23:36:09, John Hubbard wrote:
[...]
> diff --git a/man2/move_pages.2 b/man2/move_pages.2
> index 2d96468fa..1bf1053f2 100644
> --- a/man2/move_pages.2
> +++ b/man2/move_pages.2
> @@ -191,12 +191,6 @@ was specified or an attempt was made to migrate pages of a kernel thread.
>  .B ENODEV
>  One of the target nodes is not online.
>  .TP
> -.B ENOENT
> -No pages were found that require moving.
> -All pages are either already
> -on the target node, not present, had an invalid address or could not be
> -moved because they were mapped by multiple processes.
> -.TP
>  .B EPERM
>  The caller specified
>  .B MPOL_MF_MOVE_ALL
> 
> ...But I'm not sure if we should change the implementation, instead, so
> that it *can* return ENOENT. That's the main question to resolve before
> creating any more patches, I think.

I would start by dropping any note about ENOENT first. I am not really
sure there is a reasonable usecase for it but maybe somebody comes up
with something and only then we should consider it.

Feel free to add
Acked-by: Michal Hocko <mhocko@...e.com>

ideally with a kernel commit which removed the ENOENT.
-- 
Michal Hocko
SUSE Labs