Techniques index a file. The techniques involve: determining, based on a first mapping stored in a first inode associated with the file, whether a predetermined conversion condition is satisfied. The first mapping points to a plurality of data blocks of a file system storing the file in a first index structure. The techniques further involve, in response to determining that the predetermined conversion condition is satisfied, creating a second inode associated with the file. The techniques further involve converting the first mapping into a second mapping to be stored in the second inode. The second mapping points to the plurality of data blocks in a second index structure different from the first index structure.