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

[Yang Shi]

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@xxxxxxxx>
>
> 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.