On Wed, Aug 20, 2014 at 07:04:40PM +0400, Konstantin Khlebnikov wrote:
> Proper testing shows yet another problem in balloon migration: it works only
> once for each page. balloon_page_movable() check page flags and page_count.
> In __unmap_and_move page is locked, reference counter is elevated, so
> balloon_page_movable() _always_ fails here. As result in __unmap_and_move()
> migration goes to the normal migration path.
>
> Balloon ->migratepage() is so special, it returns MIGRATEPAGE_BALLOON_SUCCESS
> instead of MIGRATEPAGE_SUCCESS. After that in move_to_new_page() successfully
> migrated page got NULL into its mapping pointer and loses connectivity with
> balloon and ability for further migration.
>
> It's safe to use __is_movable_balloon_page here: page is isolated and pinned.
>
> Signed-off-by: Konstantin Khlebnikov <k.khlebnikov@xxxxxxxxxxx>
> Cc: stable <stable@xxxxxxxxxxxxxxx> # v3.8
> ---
> mm/migrate.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index f78ec9b..161d044 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -873,7 +873,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
> }
> }
>
> - if (unlikely(balloon_page_movable(page))) {
> + if (unlikely(__is_movable_balloon_page(page))) {
> /*
> * A ballooned page does not need any special attention from
> * physical to virtual reverse mapping procedures.
>
Acked-by: Rafael Aquini <aquini@xxxxxxxxxx>
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