Re: [PATCH] move_pages.2: not return ENOENT if the page are already on the target nodes

On 12/18/19 2:17 AM, Michal Hocko wrote:

On Tue 17-12-19 23:36:09, John Hubbard wrote:
[...]

quoted

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.