Re: [RESEND PATCH 4/4 v3] mm: fix possible incorrect return valueof move_pages() syscall

[Christoph Lameter]

On Sat, 28 Jul 2012, JoonSoo Kim wrote:

> 2012/7/28 Christoph Lameter <cl@xxxxxxxxx>:
> > On Sat, 28 Jul 2012, Joonsoo Kim wrote:
> >
> >> move_pages() syscall may return success in case that
> >> do_move_page_to_node_array return positive value which means migration failed.
> >
> > Nope. It only means that the migration for some pages has failed. This may
> > still be considered successful for the app if it moves 10000 pages and one
> > failed.
> >
> > This patch would break the move_pages() syscall because an error code
> > return from do_move_pages_to_node_array() will cause the status byte for
> > each page move to not be updated anymore. Application will not be able to
> > tell anymore which pages were successfully moved and which are not.
>
> In case of returning non-zero, valid status is not required according
> to man page.

Cannot find a statement like that in the man page. The return code
description is incorrect. It should that that is returns the number of
pages not moved otherwise an error code (Michael please fix the manpage).

> So, this patch would not break the move_pages() syscall.

It changes the way the system call is behaving right now.

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