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Subject: Re: [PATCH] move_pages.2: not return ENOENT if the page are already
 on the target nodes
To:     Michal Hocko <mhocko@kernel.org>,
        John Hubbard <jhubbard@nvidia.com>
Cc:     "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>,
        cl@linux.com, cai@lca.pw, akpm@linux-foundation.org,
        linux-man@vger.kernel.org, linux-api@vger.kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
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 <51dd767a-221f-882d-c7f6-45bd0c217a67@nvidia.com>
 <20191218101711.GB21485@dhcp22.suse.cz>
From:   Yang Shi <yang.shi@linux.alibaba.com>
Message-ID: <0059a598-5726-2488-cd37-b4b7f9b3353e@linux.alibaba.com>
Date:   Mon, 30 Dec 2019 19:00:43 -0800
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On 12/18/19 2:17 AM, Michal Hocko wrote:
> 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@suse.com>
>
> ideally with a kernel commit which removed the ENOENT.

A quick audit doesn't show kernel code or comment notes about ENOENT 
wrongly. The status could be set as ENOENT if the page is not present 
(follow_page() returns NULL), and man page does match what kernel does.