On Fri, Dec 06, 2013 at 01:37:26PM -0500, Naoya Horiguchi wrote:
> On Fri, Dec 06, 2013 at 03:42:16PM +0100, Vlastimil Babka wrote:
> > On 12/06/2013 09:41 AM, Joonsoo Kim wrote:
> > >migrate_pages() should return number of pages not migrated or error code.
> > >When unmap_and_move return -EAGAIN, outer loop is re-execution without
> > >initialising nr_failed. This makes nr_failed over-counted.
> > >
> > >So this patch correct it by initialising nr_failed in outer loop.
> > >
> > >Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> > >
> > >diff --git a/mm/migrate.c b/mm/migrate.c
> > >index 3747fcd..1f59ccc 100644
> > >--- a/mm/migrate.c
> > >+++ b/mm/migrate.c
> > >@@ -1102,6 +1102,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
> > >
> > > for(pass = 0; pass < 10 && retry; pass++) {
> > > retry = 0;
> > >+ nr_failed = 0;
> > >
> > > list_for_each_entry_safe(page, page2, from, lru) {
> > > cond_resched();
> > >
> >
> > If I'm reading the code correctly, unmap_and_move() (and
> > unmap_and_move_huge_page() as well) deletes all pages from the
> > 'from' list, unless it fails with -EAGAIN. So the only pages you see
> > in subsequent passes are those that failed with -EAGAIN and those
> > are not counted as nr_failed. So there shouldn't be over-count, but
> > your patch could result in under-count.
> >
> > Perhaps a comment somewhere would clarify this.
>
> I agree and suggest the one below.
> Joonsoo, feel free to append it to your series:)
>
> Thanks,
> Naoya Horiguchi
> ---
> From: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> Date: Fri, 6 Dec 2013 13:08:15 -0500
> Subject: [PATCH] migrate: add comment about permanent failure path
>
> Let's add a comment about where the failed page goes to, which makes
> code more readable.
>
> Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> ---
> mm/migrate.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 661ff5f66591..c01caafa0a6f 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1118,7 +1118,12 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
> nr_succeeded++;
> break;
> default:
> - /* Permanent failure */
> + /*
> + * Permanent failure (-EBUSY, -ENOSYS, etc.):
> + * unlike -EAGAIN case, the failed page is
> + * removed from migration page list and not
> + * retried in the next outer loop.
> + */
> nr_failed++;
> break;
> }
> --
> 1.8.3.1
Hello, Naoya.
When I saw this new comment, I found that unmap_and_move_huge_page()
has a bug. It would not remove the page from the list if
hugepage_migration_support() is false.
I will include your patch into my series and send an additional patch to fix
this problem.
Thanks.
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