mm/filemap: Add folio_end_writeback()

Add an end_page_writeback() wrapper function for users that are not yet
converted to folios.

folio_end_writeback() is less than half the size of end_page_writeback()
at just 105 bytes compared to 228 bytes, due to removing all the
compound_head() calls.  The 30 byte wrapper function makes this a net
saving of 93 bytes.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Jeff Layton <jlayton@kernel.org>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Reviewed-by: David Howells <dhowells@redhat.com>
Acked-by: Mike Rapoport <rppt@linux.ibm.com>

include/linux/pagemap.h

@@ -767,7 +767,8 @@ static inline int wait_on_page_locked_killable(struct page *page)
 int put_and_wait_on_page_locked(struct page *page, int state);
 void wait_on_page_writeback(struct page *page);
 int wait_on_page_writeback_killable(struct page *page);
-extern void end_page_writeback(struct page *page);
+void end_page_writeback(struct page *page);
+void folio_end_writeback(struct folio *folio);
 void wait_for_stable_page(struct page *page);
 
 void __set_page_dirty(struct page *, struct address_space *, int warn);

mm/filemap.c

@@ -1230,11 +1230,11 @@ static void wake_up_page_bit(struct page *page, int bit_nr)
 	spin_unlock_irqrestore(&q->lock, flags);
 }
 
-static void wake_up_page(struct page *page, int bit)
+static void folio_wake(struct folio *folio, int bit)
 {
-	if (!PageWaiters(page))
+	if (!folio_test_waiters(folio))
 		return;
-	wake_up_page_bit(page, bit);
+	wake_up_page_bit(&folio->page, bit);
 }
 
 /*
@@ -1571,39 +1571,38 @@ int wait_on_page_private_2_killable(struct page *page)
 EXPORT_SYMBOL(wait_on_page_private_2_killable);
 
 /**
- * end_page_writeback - end writeback against a page
- * @page: the page
+ * folio_end_writeback - End writeback against a folio.
+ * @folio: The folio.
  */
-void end_page_writeback(struct page *page)
+void folio_end_writeback(struct folio *folio)
 {
 	/*
-	 * TestClearPageReclaim could be used here but it is an atomic
-	 * operation and overkill in this particular case. Failing to
-	 * shuffle a page marked for immediate reclaim is too mild to
-	 * justify taking an atomic operation penalty at the end of
-	 * ever page writeback.
+	 * folio_test_clear_reclaim() could be used here but it is an
+	 * atomic operation and overkill in this particular case. Failing
+	 * to shuffle a folio marked for immediate reclaim is too mild
+	 * a gain to justify taking an atomic operation penalty at the
+	 * end of every folio writeback.
 	 */
-	if (PageReclaim(page)) {
-		struct folio *folio = page_folio(page);
-		ClearPageReclaim(page);
+	if (folio_test_reclaim(folio)) {
+		folio_clear_reclaim(folio);
 		folio_rotate_reclaimable(folio);
 	}
 
 	/*
-	 * Writeback does not hold a page reference of its own, relying
+	 * Writeback does not hold a folio reference of its own, relying
 	 * on truncation to wait for the clearing of PG_writeback.
-	 * But here we must make sure that the page is not freed and
-	 * reused before the wake_up_page().
+	 * But here we must make sure that the folio is not freed and
+	 * reused before the folio_wake().
 	 */
-	get_page(page);
-	if (!test_clear_page_writeback(page))
+	folio_get(folio);
+	if (!test_clear_page_writeback(&folio->page))
 		BUG();
 
 	smp_mb__after_atomic();
-	wake_up_page(page, PG_writeback);
-	put_page(page);
+	folio_wake(folio, PG_writeback);
+	folio_put(folio);
 }
-EXPORT_SYMBOL(end_page_writeback);
+EXPORT_SYMBOL(folio_end_writeback);
 
 /*
  * After completing I/O on a page, call this routine to update the page

mm/folio-compat.c

@@ -17,3 +17,9 @@ void unlock_page(struct page *page)
 	return folio_unlock(page_folio(page));
 }
 EXPORT_SYMBOL(unlock_page);
+
+void end_page_writeback(struct page *page)
+{
+	return folio_end_writeback(page_folio(page));
+}
+EXPORT_SYMBOL(end_page_writeback);