Re: [PATCH] Fix do_move_pages_to_node() error handling

[Michal Hocko <mhocko@suse.com>]

On Wed 14-11-18 08:34:15, Michal Hocko wrote:
> On Tue 13-11-18 16:40:59, p.jaroszynski@gmail.com wrote:
> > From: Piotr Jaroszynski <pjaroszynski@nvidia.com>
> > 
> > migrate_pages() can return the number of pages that failed to migrate
> > instead of 0 or an error code. If that happens, the positive return is
> > treated as an error all the way up through the stack leading to the
> > move_pages() syscall returning a positive number. I believe this
> > regressed with commit a49bd4d71637 ("mm, numa: rework do_pages_move")
> > that refactored a lot of this code.
> 
> Yes this is correct.
> 
> > Fix this by treating positive returns as success in
> > do_move_pages_to_node() as that seems to most closely follow the
> > previous code. This still leaves the question whether silently
> > considering this case a success is the right thing to do as even the
> > status of the pages will be set as if they were successfully migrated,
> > but that seems to have been the case before as well.
> 
> Yes, I believe the previous semantic was just wrong and we want to fix
> it. Jan has already brought this up [1]. I believe we want to update the
> documentation rather than restore the previous hazy semantic.
> 
> Just wondering, how have you found out? Is there any real application
> failing because of the change or this is a result of some test?
> 
> [1] http://lkml.kernel.org/r/0329efa0984b9b0252ef166abb4498c0795fab36.1535113317.git.jstancek@redhat.com

Btw. this is what I was suggesting back then (along with the man page
update suggested by Jan)