mm: move get_page_from_free_area() to mm/page_alloc.c

The get_page_from_free_area() helper is only used in mm/page_alloc.c so
move it there to reduce noise in include/linux/mmzone.h

Link: https://lkml.kernel.org/r/20230319114214.2133332-1-rppt@kernel.orgSigned-off-by: Mike Rapoport (IBM) <rppt@kernel.org>
Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/mmzone.h

@@ -108,13 +108,6 @@ struct free_area {
 	unsigned long		nr_free;
 };
 
-static inline struct page *get_page_from_free_area(struct free_area *area,
-					    int migratetype)
-{
-	return list_first_entry_or_null(&area->free_list[migratetype],
-					struct page, lru);
-}
-
 static inline bool free_area_empty(struct free_area *area, int migratetype)
 {
 	return list_empty(&area->free_list[migratetype]);

mm/page_alloc.c

@@ -1048,6 +1048,13 @@ static inline void del_page_from_free_list(struct page *page, struct zone *zone,
 	zone->free_area[order].nr_free--;
 }
 
+static inline struct page *get_page_from_free_area(struct free_area *area,
+					    int migratetype)
+{
+	return list_first_entry_or_null(&area->free_list[migratetype],
+					struct page, lru);
+}
+
 /*
  * If this is not the largest possible page, check if the buddy
  * of the next-highest order is free. If it is, it's possible