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: <51dd767a-221f-882d-c7f6-45bd0c217a67@nvidia.com>
Date:   Tue, 17 Dec 2019 23:36:09 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
        Yang Shi <yang.shi@...ux.alibaba.com>, <cl@...ux.com>,
        <mhocko@...e.com>, <cai@....pw>, <akpm@...ux-foundation.org>
CC:     <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 12/13/19 5:55 PM, Michael Kerrisk (man-pages) wrote:
...
>>> 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?
> 

I was waiting to see if Yang was going to respond...anyway, I think
we're looking at approximately this sort of change:

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.

In addition, Michal mentioned that the page states in the status array also
need updated documentation.


thanks,
-- 
John Hubbard
NVIDIA