mm: add private field of first tail to struct page and struct folio

Allow struct folio to store hugetlb metadata that is contained in the
private field of the first tail page.  On 32-bit, _private_1 aligns with
page[1].private.

Link: https://lkml.kernel.org/r/20220922154207.1575343-3-sidhartha.kumar@oracle.comSigned-off-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Acked-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Colin Cross <ccross@google.com>
Cc: David Howells <dhowells@redhat.com>
Cc: "Eric W . Biederman" <ebiederm@xmission.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: kernel test robot <lkp@intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: William Kucharski <william.kucharski@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/mm_types.h

@@ -144,6 +144,7 @@ struct page {
 			atomic_t compound_pincount;
 #ifdef CONFIG_64BIT
 			unsigned int compound_nr; /* 1 << compound_order */
+			unsigned long _private_1;
 #endif
 		};
 		struct {	/* Second tail page of compound page */
@@ -264,6 +265,7 @@ struct page {
  * @_total_mapcount: Do not use directly, call folio_entire_mapcount().
  * @_pincount: Do not use directly, call folio_maybe_dma_pinned().
  * @_folio_nr_pages: Do not use directly, call folio_nr_pages().
+ * @_private_1: Do not use directly, call folio_get_private_1().
  *
  * A folio is a physically, virtually and logically contiguous set
  * of bytes.  It is a power-of-two in size, and it is aligned to that
@@ -311,6 +313,7 @@ struct folio {
 #ifdef CONFIG_64BIT
 	unsigned int _folio_nr_pages;
 #endif
+	unsigned long _private_1;
 };
 
 #define FOLIO_MATCH(pg, fl)						\
@@ -338,6 +341,7 @@ FOLIO_MATCH(compound_mapcount, _total_mapcount);
 FOLIO_MATCH(compound_pincount, _pincount);
 #ifdef CONFIG_64BIT
 FOLIO_MATCH(compound_nr, _folio_nr_pages);
+FOLIO_MATCH(_private_1, _private_1);
 #endif
 #undef FOLIO_MATCH
 
@@ -383,6 +387,16 @@ static inline void *folio_get_private(struct folio *folio)
 	return folio->private;
 }
 
+static inline void folio_set_private_1(struct folio *folio, unsigned long private)
+{
+	folio->_private_1 = private;
+}
+
+static inline unsigned long folio_get_private_1(struct folio *folio)
+{
+	return folio->_private_1;
+}
+
 struct page_frag_cache {
 	void * va;
 #if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE)