ext4: convert ac_buddy_page to ac_buddy_folio

This just carries around the bd_buddy_folio so should also be a folio.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Link: https://lore.kernel.org/r/20240416172900.244637-6-willy@infradead.orgSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/mballoc.c

@@ -2163,8 +2163,8 @@ static void ext4_mb_use_best_found(struct ext4_allocation_context *ac,
 	 */
 	ac->ac_bitmap_folio = e4b->bd_bitmap_folio;
 	folio_get(ac->ac_bitmap_folio);
-	ac->ac_buddy_page = &e4b->bd_buddy_folio->page;
-	get_page(ac->ac_buddy_page);
+	ac->ac_buddy_folio = e4b->bd_buddy_folio;
+	folio_get(ac->ac_buddy_folio);
 	/* store last allocated for subsequent stream allocation */
 	if (ac->ac_flags & EXT4_MB_STREAM_ALLOC) {
 		spin_lock(&sbi->s_md_lock);
@@ -6004,8 +6004,8 @@ static void ext4_mb_release_context(struct ext4_allocation_context *ac)
 	}
 	if (ac->ac_bitmap_folio)
 		folio_put(ac->ac_bitmap_folio);
-	if (ac->ac_buddy_page)
-		put_page(ac->ac_buddy_page);
+	if (ac->ac_buddy_folio)
+		folio_put(ac->ac_buddy_folio);
 	if (ac->ac_flags & EXT4_MB_HINT_GROUP_ALLOC)
 		mutex_unlock(&ac->ac_lg->lg_mutex);
 	ext4_mb_collect_stats(ac);

fs/ext4/mballoc.h

@@ -205,7 +205,7 @@ struct ext4_allocation_context {
 				 * N > 0, the field stores N, otherwise 0 */
 	__u8 ac_op;		/* operation, for history only */
 	struct folio *ac_bitmap_folio;
-	struct page *ac_buddy_page;
+	struct folio *ac_buddy_folio;
 	struct ext4_prealloc_space *ac_pa;
 	struct ext4_locality_group *ac_lg;
 };