mm: Add folio_nid()

This is the folio equivalent of page_to_nid().
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Mike Rapoport <rppt@linux.ibm.com>
Reviewed-by: David Howells <dhowells@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>

include/linux/mm.h

@@ -1429,6 +1429,11 @@ static inline int page_to_nid(const struct page *page)
 }
 #endif
 
+static inline int folio_nid(const struct folio *folio)
+{
+	return page_to_nid(&folio->page);
+}
+
 #ifdef CONFIG_NUMA_BALANCING
 static inline int cpu_pid_to_cpupid(int cpu, int pid)
 {