On Thu, Aug 05, 2021 at 11:05:56PM +0800, Baolin Wang wrote:
> We've got the expected count for anonymous page or file page by
> expected_page_refs() at the beginning of migrate_page_move_mapping(),
> thus we should move the page count validation a little forward to
> reduce duplicated code.
Please add an explanation to the changelog for why it's safe to pull
this out from under the i_pages lock.
> Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> ---
> mm/migrate.c | 10 ++++------
> 1 file changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 239b238..5559571 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -386,11 +386,10 @@ int folio_migrate_mapping(struct address_space *mapping,
> int expected_count = expected_page_refs(mapping, &folio->page) + extra_count;
> long nr = folio_nr_pages(folio);
>
> - if (!mapping) {
> - /* Anonymous page without mapping */
> - if (folio_ref_count(folio) != expected_count)
> - return -EAGAIN;
> + if (folio_ref_count(folio) != expected_count)
> + return -EAGAIN;
>
> + if (!mapping) {
> /* No turning back from here */
> newfolio->index = folio->index;
> newfolio->mapping = folio->mapping;
> @@ -404,8 +403,7 @@ int folio_migrate_mapping(struct address_space *mapping,
> newzone = folio_zone(newfolio);
>
> xas_lock_irq(&xas);
> - if (folio_ref_count(folio) != expected_count ||
> - xas_load(&xas) != folio) {
> + if (xas_load(&xas) != folio) {
> xas_unlock_irq(&xas);
> return -EAGAIN;
> }
> --
> 1.8.3.1
>
>
