How to free data block of ext2 fs?

Hi all , I wanted to free a data block from disk. So I made a loop device for ext2 fs and inserted my module(code) through insmod command. Here are the details : I found a function named ext2_free_data() which takes block numbers to be freed as a parameter. The declaration of the function is as follows : void ext2_free_data(struct inode *inode, __le32 *p, __le32 *q); As we can see this function use structure of inode object and it make changes in this inode object. This function changes the fields in in-core inode and mark the inode dirty. But I want the changes made in in-core inode to be reflected in disk inode immediately . Is there any command to flush the buffers ? -- Regards, Kashish