doc: correct struct folio kernel-doc

Insert appropriate public: and private: markers to make the generated
kernel-doc look right.

Link: https://lkml.kernel.org/r/20230111142915.1001531-24-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/mm_types.h

@@ -292,16 +292,12 @@ static inline struct page *encoded_page_ptr(struct encoded_page *page)
  * @_refcount: Do not access this member directly.  Use folio_ref_count()
  *    to find how many references there are to this folio.
  * @memcg_data: Memory Control Group data.
- * @_flags_1: For large folios, additional page flags.
- * @_head_1: Points to the folio.  Do not use.
  * @_folio_dtor: Which destructor to use for this folio.
  * @_folio_order: Do not use directly, call folio_order().
  * @_entire_mapcount: Do not use directly, call folio_entire_mapcount().
  * @_nr_pages_mapped: Do not use directly, call folio_mapcount().
  * @_pincount: Do not use directly, call folio_maybe_dma_pinned().
  * @_folio_nr_pages: Do not use directly, call folio_nr_pages().
- * @_flags_2: For alignment.  Do not use.
- * @_head_2: Points to the folio.  Do not use.
  * @_hugetlb_subpool: Do not use directly, use accessor in hugetlb.h.
  * @_hugetlb_cgroup: Do not use directly, use accessor in hugetlb_cgroup.h.
  * @_hugetlb_cgroup_rsvd: Do not use directly, use accessor in hugetlb_cgroup.h.
@@ -348,6 +344,7 @@ struct folio {
 		struct {
 			unsigned long _flags_1;
 			unsigned long _head_1;
+	/* public: */
 			unsigned char _folio_dtor;
 			unsigned char _folio_order;
 			atomic_t _entire_mapcount;
@@ -356,6 +353,7 @@ struct folio {
 #ifdef CONFIG_64BIT
 			unsigned int _folio_nr_pages;
 #endif
+	/* private: the union with struct page is transitional */
 		};
 		struct page __page_1;
 	};
@@ -363,10 +361,12 @@ struct folio {
 		struct {
 			unsigned long _flags_2;
 			unsigned long _head_2;
+	/* public: */
 			void *_hugetlb_subpool;
 			void *_hugetlb_cgroup;
 			void *_hugetlb_cgroup_rsvd;
 			void *_hugetlb_hwpoison;
+	/* private: the union with struct page is transitional */
 		};
 		struct page __page_2;
 	};