mm: simplify folio_expected_ref_count()

Now that PAGE_MAPPING_MOVABLE is gone, we can simplify and rely on the
folio_test_anon() test only.

... but staring at the users, this function should never even have been
called on movable_ops pages. E.g.,
* __buffer_migrate_folio() does not make sense for them
* folio_migrate_mapping() does not make sense for them
* migrate_huge_page_move_mapping() does not make sense for them
* __migrate_folio() does not make sense for them
* ... and khugepaged should never stumble over them

Let's simply refuse typed pages (which includes slab) except hugetlb, and
WARN.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: David Hildenbrand <[email protected]>
Reviewed-by: Zi Yan <[email protected]>
Reviewed-by: Lorenzo Stoakes <[email protected]>
Reviewed-by: Harry Yoo <[email protected]>
Cc: Alistair Popple <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Brendan Jackman <[email protected]>
Cc: Byungchul Park <[email protected]>
Cc: Chengming Zhou <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Christophe Leroy <[email protected]>
Cc: Eugenio Pé rez <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Gregory Price <[email protected]>
Cc: "Huang, Ying" <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: Jason Wang <[email protected]>
Cc: Jerrin Shaji George <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: John Hubbard <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Joshua Hahn <[email protected]>
Cc: Liam Howlett <[email protected]>
Cc: Madhavan Srinivasan <[email protected]>
Cc: Mathew Brost <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: Miaohe Lin <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: "Michael S. Tsirkin" <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Cc: Nicholas Piggin <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: Qi Zheng <[email protected]>
Cc: Rakie Kim <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Sergey Senozhatsky <[email protected]>
Cc: Shakeel Butt <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Xuan Zhuo <[email protected]>
Cc: xu xin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

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