nilfs2: convert nilfs_btnode_prepare_change_key to use a folio

Saves three calls to compound_head().

Link: https://lkml.kernel.org/r/20231114084436.2755-19-konishi.ryusuke@gmail.comSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/nilfs2/btnode.c

@@ -185,23 +185,23 @@ int nilfs_btnode_prepare_change_key(struct address_space *btnc,
 	ctxt->newbh = NULL;
 
 	if (inode->i_blkbits == PAGE_SHIFT) {
-		struct page *opage = obh->b_page;
-		lock_page(opage);
+		struct folio *ofolio = obh->b_folio;
+		folio_lock(ofolio);
 retry:
 		/* BUG_ON(oldkey != obh->b_folio->index); */
-		if (unlikely(oldkey != opage->index))
-			NILFS_PAGE_BUG(opage,
+		if (unlikely(oldkey != ofolio->index))
+			NILFS_PAGE_BUG(&ofolio->page,
 				       "invalid oldkey %lld (newkey=%lld)",
 				       (unsigned long long)oldkey,
 				       (unsigned long long)newkey);
 
 		xa_lock_irq(&btnc->i_pages);
-		err = __xa_insert(&btnc->i_pages, newkey, opage, GFP_NOFS);
+		err = __xa_insert(&btnc->i_pages, newkey, ofolio, GFP_NOFS);
 		xa_unlock_irq(&btnc->i_pages);
 		/*
-		 * Note: page->index will not change to newkey until
+		 * Note: folio->index will not change to newkey until
 		 * nilfs_btnode_commit_change_key() will be called.
-		 * To protect the page in intermediate state, the page lock
+		 * To protect the folio in intermediate state, the folio lock
 		 * is held.
 		 */
 		if (!err)
@@ -213,7 +213,7 @@ int nilfs_btnode_prepare_change_key(struct address_space *btnc,
 		if (!err)
 			goto retry;
 		/* fallback to copy mode */
-		unlock_page(opage);
+		folio_unlock(ofolio);
 	}
 
 	nbh = nilfs_btnode_create_block(btnc, newkey);
@@ -225,7 +225,7 @@ int nilfs_btnode_prepare_change_key(struct address_space *btnc,
 	return 0;
 
  failed_unlock:
-	unlock_page(obh->b_page);
+	folio_unlock(obh->b_folio);
 	return err;
 }