The memcg_data is only set on the head page, so enforce that by
typing it as a folio.
Signed-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Acked-by: NMichal Hocko <mhocko@suse.com>
Reviewed-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NVlastimil Babka <vbabka@suse.cz>