ext4: limit the maximum folio order

In environments with a page size of 64KB, the maximum size of a folio
can reach up to 128MB. Consequently, during the write-back of folios,
the 'rsv_blocks' will be overestimated to 1,577, which can make
pressure on the journal space where the journal is small. This can
easily exceed the limit of a single transaction. Besides, an excessively
large folio is meaningless and will instead increase the overhead of
traversing the bhs within the folio. Therefore, limit the maximum order
of a folio to 2048 filesystem blocks.

Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Reported-by: Joseph Qi <jiangqi903@gmail.com>
Closes: https://lore.kernel.org/linux-ext4/CA+G9fYsyYQ3ZL4xaSg1-Tt5Evto7Zd+hgNWZEa9cQLbahA1+xg@mail.gmail.com/
Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Tested-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20250707140814.542883-12-yi.zhang@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Author: zhangyi089

fs/ext4/ext4.h

@@ -3020,7 +3020,7 @@ int ext4_walk_page_buffers(handle_t *handle,
 				     struct buffer_head *bh));
 int do_journal_get_write_access(handle_t *handle, struct inode *inode,
 				struct buffer_head *bh);
-bool ext4_should_enable_large_folio(struct inode *inode);
+void ext4_set_inode_mapping_order(struct inode *inode);
 #define FALL_BACK_TO_NONDELALLOC 1
 #define CONVERT_INLINE_DATA	 2
 

fs/ext4/ialloc.c

@@ -1335,8 +1335,7 @@ struct inode *__ext4_new_inode(struct mnt_idmap *idmap,
 		}
 	}
 
-	if (ext4_should_enable_large_folio(inode))
-		mapping_set_large_folios(inode->i_mapping);
+	ext4_set_inode_mapping_order(inode);
 
 	ext4_update_inode_fsync_trans(handle, inode, 1);
 

fs/ext4/inode.c

@@ -5179,7 +5179,7 @@ static int check_igot_inode(struct inode *inode, ext4_iget_flags flags,
 	return -EFSCORRUPTED;
 }
 
-bool ext4_should_enable_large_folio(struct inode *inode)
+static bool ext4_should_enable_large_folio(struct inode *inode)
 {
 	struct super_block *sb = inode->i_sb;
 
@@ -5196,6 +5196,22 @@ bool ext4_should_enable_large_folio(struct inode *inode)
 	return true;
 }
 
+/*
+ * Limit the maximum folio order to 2048 blocks to prevent overestimation
+ * of reserve handle credits during the folio writeback in environments
+ * where the PAGE_SIZE exceeds 4KB.
+ */
+#define EXT4_MAX_PAGECACHE_ORDER(i)		\
+		umin(MAX_PAGECACHE_ORDER, (11 + (i)->i_blkbits - PAGE_SHIFT))
+void ext4_set_inode_mapping_order(struct inode *inode)
+{
+	if (!ext4_should_enable_large_folio(inode))
+		return;
+
+	mapping_set_folio_order_range(inode->i_mapping, 0,
+				      EXT4_MAX_PAGECACHE_ORDER(inode));
+}
+
 struct inode *__ext4_iget(struct super_block *sb, unsigned long ino,
 			  ext4_iget_flags flags, const char *function,
 			  unsigned int line)
@@ -5513,8 +5529,8 @@ struct inode *__ext4_iget(struct super_block *sb, unsigned long ino,
 		ret = -EFSCORRUPTED;
 		goto bad_inode;
 	}
-	if (ext4_should_enable_large_folio(inode))
-		mapping_set_large_folios(inode->i_mapping);
+
+	ext4_set_inode_mapping_order(inode);
 
 	ret = check_igot_inode(inode, flags, function, line);
 	/*