Phoronix posted an article on the performance of EXT4 then & now

Over the past week there has been a lot of talk about the EXT4 file-system following the announcement that Google is migrating their EXT2 file-systems to EXT4. Their reasons for this transition to EXT4 are attributed to the easy migration process and Google engineers are pleased with this file-system's performance. However, as we mentioned in that news post last week and in many other articles over the past weeks and months, EXT4 is not as great of a contender as it was in the past, well, for some tests at least. The performance of the EXT4 file-system commonly goes down with new kernel releases and not up, as kernel developers continue to introduce new safeguards to address potential data loss problems that initially plagued some EXT4 users. For our latest EXT4 benchmarks we have numbers that show this file-system's performance using a vanilla 2.6.28 kernel (when EXT4 was marked as stable) and then every major kernel release up through the latest Linux 2.6.33 release candidate.

The Performance Of EXT4 Then & Now