Btrfs: add a comment for fs_info->max_inline

index 745e7ad..3e672916 100644
@@ -1288,6 +1288,12 @@ struct btrfs_fs_info {
 	atomic64_t last_trans_log_full_commit;
 	unsigned long mount_opt;
 	unsigned long compress_type:4;
+	/*
+	 * It is a suggestive number, the read side is safe even it gets a
+	 * wrong number because we will write out the data into a regular
+	 * extent. The write side(mount/remount) is under ->s_umount lock,
+	 * so it is also safe.
+	 */
 	u64 max_inline;
 	u64 alloc_start;
 	struct btrfs_transaction *running_transaction;