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: <092adc11-7039-9343-7067-0e0199c9dc13@gmail.com>
Date:   Sat, 14 Dec 2019 02:55:15 +0100
From:   "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:     Yang Shi <yang.shi@...ux.alibaba.com>,
        John Hubbard <jhubbard@...dia.com>, cl@...ux.com,
        mhocko@...e.com, cai@....pw, akpm@...ux-foundation.org
Cc:     mtk.manpages@...il.com, 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 12/6/19 6:26 PM, Yang Shi wrote:
> 
> 
> On 12/6/19 12:25 AM, John Hubbard wrote:
>> 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@...il.com>
>>> Cc: Christoph Lameter <cl@...ux.com>
>>> Cc: John Hubbard <jhubbard@...dia.com>
>>> Cc: Michal Hocko <mhocko@...e.com>
>>> Cc: Qian Cai <cai@....pw>
>>> Signed-off-by: Yang Shi <yang.shi@...ux.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?
> 
> Nice catch. Yes, you are right.
> 
>>
>> If so, we need to redo this part of the man page.
> 
> Yes.

So where are things at with this? Is an improved man-pages 
patch on the way, or is some other action (on the API) planned?

Thanks,

Michael


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