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From:   ebiederm@xmission.com (Eric W. Biederman)
To:     Yang Shi <yang.shi@linux.alibaba.com>
Cc:     Michal Hocko <mhocko@kernel.org>,
        John Hubbard <jhubbard@nvidia.com>,
        "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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        <95170ea5-5b62-9168-fcd9-93b43330a1b4@linux.alibaba.com>
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        <51dd767a-221f-882d-c7f6-45bd0c217a67@nvidia.com>
        <20191218101711.GB21485@dhcp22.suse.cz>
        <0059a598-5726-2488-cd37-b4b7f9b3353e@linux.alibaba.com>
Date:   Mon, 30 Dec 2019 21:49:03 -0600
In-Reply-To: <0059a598-5726-2488-cd37-b4b7f9b3353e@linux.alibaba.com> (Yang
        Shi's message of "Mon, 30 Dec 2019 19:00:43 -0800")
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Subject: Re: [PATCH] move_pages.2: not return ENOENT if the page are already on the target nodes
Sender: linux-kernel-owner@vger.kernel.org
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Yang Shi <yang.shi@linux.alibaba.com> writes:

> 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.

Doesn't the function one layer up then consume the ENOENT?

Eric