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Subject: Re: [PATCH] move_pages.2: not return ENOENT if the page are already
 on the target nodes
To:     Yang Shi <yang.shi@linux.alibaba.com>, <mtk.manpages@gmail.com>,
        <cl@linux.com>, <mhocko@suse.com>, <cai@lca.pw>,
        <akpm@linux-foundation.org>
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        <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>
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From:   John Hubbard <jhubbard@nvidia.com>
Message-ID: <0dc96e40-5f2b-a2fe-6e5f-b6f3d5e9ebde@nvidia.com>
Date:   Fri, 6 Dec 2019 00:25:53 -0800
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On 12/5/19 5:34 PM, Yang Shi wrote:
> Since commit e78bbfa82624 ("mm: stop returning -ENOENT
> from sys_move_pages() if nothing got migrated"), move_pages doesn't
> return -ENOENT anymore if the pages are already on the target nodes, but
> this change is never reflected in manpage.
> 
> Cc: Michael Kerrisk <mtk.manpages@gmail.com>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: John Hubbard <jhubbard@nvidia.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Qian Cai <cai@lca.pw>
> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
> ---
>   man2/move_pages.2 | 5 ++---
>   1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/man2/move_pages.2 b/man2/move_pages.2
> index 2d96468..2a2f3cd 100644
> --- a/man2/move_pages.2
> +++ b/man2/move_pages.2
> @@ -192,9 +192,8 @@ was specified or an attempt was made to migrate pages of a kernel thread.
>   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
> +No pages were found.
> +All pages are either not present, had an invalid address or could not be
>   moved because they were mapped by multiple processes.
>   .TP
>   .B EPERM
> 

whoa, hold on. If I'm reading through the various error paths correctly, then this
code is *never* going to return ENOENT for the whole function. It can fill in that
value per-page, in the status array, but that's all. Did I get that right?

If so, we need to redo this part of the man page.


thanks,
-- 
John Hubbard
NVIDIA