mm/filemap: Add folio private_2 functions

end_page_private_2() becomes folio_end_private_2(),
wait_on_page_private_2() becomes folio_wait_private_2() and
wait_on_page_private_2_killable() becomes folio_wait_private_2_killable().

Adjust the fscache equivalents to call page_folio() before calling these
functions to avoid adding wrappers.  Ends up costing 1 byte of text
in ceph & netfs, but the core shrinks by three calls to page_folio().
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Howells <dhowells@redhat.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

include/linux/netfs.h

@@ -55,7 +55,7 @@ static inline void set_page_fscache(struct page *page)
  */
 static inline void end_page_fscache(struct page *page)
 {
-	end_page_private_2(page);
+	folio_end_private_2(page_folio(page));
 }
 
 /**
@@ -66,7 +66,7 @@ static inline void end_page_fscache(struct page *page)
  */
 static inline void wait_on_page_fscache(struct page *page)
 {
-	wait_on_page_private_2(page);
+	folio_wait_private_2(page_folio(page));
 }
 
 /**
@@ -82,7 +82,7 @@ static inline void wait_on_page_fscache(struct page *page)
  */
 static inline int wait_on_page_fscache_killable(struct page *page)
 {
-	return wait_on_page_private_2_killable(page);
+	return folio_wait_private_2_killable(page_folio(page));
 }
 
 enum netfs_read_source {

include/linux/pagemap.h

@@ -795,9 +795,9 @@ static inline void set_page_private_2(struct page *page)
 	SetPagePrivate2(page);
 }
 
-void end_page_private_2(struct page *page);
-void wait_on_page_private_2(struct page *page);
-int wait_on_page_private_2_killable(struct page *page);
+void folio_end_private_2(struct folio *folio);
+void folio_wait_private_2(struct folio *folio);
+int folio_wait_private_2_killable(struct folio *folio);
 
 /*
  * Add an arbitrary waiter to a page's wait queue

mm/filemap.c

@@ -1506,56 +1506,51 @@ void folio_unlock(struct folio *folio)
 EXPORT_SYMBOL(folio_unlock);
 
 /**
- * end_page_private_2 - Clear PG_private_2 and release any waiters
- * @page: The page
+ * folio_end_private_2 - Clear PG_private_2 and wake any waiters.
+ * @folio: The folio.
  *
- * Clear the PG_private_2 bit on a page and wake up any sleepers waiting for
- * this.  The page ref held for PG_private_2 being set is released.
+ * Clear the PG_private_2 bit on a folio and wake up any sleepers waiting for
+ * it.  The folio reference held for PG_private_2 being set is released.
  *
- * This is, for example, used when a netfs page is being written to a local
- * disk cache, thereby allowing writes to the cache for the same page to be
+ * This is, for example, used when a netfs folio is being written to a local
+ * disk cache, thereby allowing writes to the cache for the same folio to be
  * serialised.
  */
-void end_page_private_2(struct page *page)
+void folio_end_private_2(struct folio *folio)
 {
-	struct folio *folio = page_folio(page);
-
 	VM_BUG_ON_FOLIO(!folio_test_private_2(folio), folio);
 	clear_bit_unlock(PG_private_2, folio_flags(folio, 0));
 	folio_wake_bit(folio, PG_private_2);
 	folio_put(folio);
 }
-EXPORT_SYMBOL(end_page_private_2);
+EXPORT_SYMBOL(folio_end_private_2);
 
 /**
- * wait_on_page_private_2 - Wait for PG_private_2 to be cleared on a page
- * @page: The page to wait on
+ * folio_wait_private_2 - Wait for PG_private_2 to be cleared on a folio.
+ * @folio: The folio to wait on.
  *
- * Wait for PG_private_2 (aka PG_fscache) to be cleared on a page.
+ * Wait for PG_private_2 (aka PG_fscache) to be cleared on a folio.
  */
-void wait_on_page_private_2(struct page *page)
+void folio_wait_private_2(struct folio *folio)
 {
-	struct folio *folio = page_folio(page);
-
 	while (folio_test_private_2(folio))
 		folio_wait_bit(folio, PG_private_2);
 }
-EXPORT_SYMBOL(wait_on_page_private_2);
+EXPORT_SYMBOL(folio_wait_private_2);
 
 /**
- * wait_on_page_private_2_killable - Wait for PG_private_2 to be cleared on a page
- * @page: The page to wait on
+ * folio_wait_private_2_killable - Wait for PG_private_2 to be cleared on a folio.
+ * @folio: The folio to wait on.
  *
- * Wait for PG_private_2 (aka PG_fscache) to be cleared on a page or until a
+ * Wait for PG_private_2 (aka PG_fscache) to be cleared on a folio or until a
  * fatal signal is received by the calling task.
  *
  * Return:
  * - 0 if successful.
  * - -EINTR if a fatal signal was encountered.
  */
-int wait_on_page_private_2_killable(struct page *page)
+int folio_wait_private_2_killable(struct folio *folio)
 {
-	struct folio *folio = page_folio(page);
 	int ret = 0;
 
 	while (folio_test_private_2(folio)) {
@@ -1566,7 +1561,7 @@ int wait_on_page_private_2_killable(struct page *page)
 
 	return ret;
 }
-EXPORT_SYMBOL(wait_on_page_private_2_killable);
+EXPORT_SYMBOL(folio_wait_private_2_killable);
 
 /**
  * folio_end_writeback - End writeback against a folio.