Re: [PATCH 3/6] mm/page_owner: copy last_migrate_reason in copy_page_owner()

[Joonsoo Kim]

On Tue, May 10, 2016 at 05:13:12PM +0200, Vlastimil Babka wrote:
> On 05/03/2016 07:23 AM, js1304@xxxxxxxxx wrote:
> >From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> >
> >Currently, copy_page_owner() doesn't copy all the owner information.
> >It skips last_migrate_reason because copy_page_owner() is used for
> >migration and it will be properly set soon. But, following patch
> >will use copy_page_owner() and this skip will cause the problem that
> >allocated page has uninitialied last_migrate_reason. To prevent it,
> >this patch also copy last_migrate_reason in copy_page_owner().
> 
> Hmm it's a corner case, but if the "new" page was dumped e.g. due to
> a bug during the migration, is the copied migrate reason from the
> "old" page actually meaningful? I'd say it might be misleading and
> it's simpler to just make sure it's initialized to -1.

Hmm... if it is the case, other fields are also misleading. I think
that we can tolerate this corner case and keeping function semantic as
function name suggests is better practice.

Thanks.