I just wanted to share some findings and see if anyone else has these problems. Recently I did a fresh install of Ubuntu 9.04 with Ext4 (to see how it goes). For my thesis I have a classification problem which requires importing quite big amounts of data from CSV file into a simple database.
When I run this program I noticed that FireFox 3 almost froze up completely up to 1 minute. Other apps got micro-freezes too but much less. I read about ext[2,3,4] file-system problems in regards to fsync() and the new scheduler in some articles.
As an experiment I did a fresh reinstall with reiserFS and the problem is gone. I can work while my importer runs in the background with minimal slowdowns.
So to sum it up it seems that the EXT family of filesystems combined with the current IO system and scheduler in the kernel has some serious locking problems. Anyone else noticed this?
From what I've heard, this is supposed to be fixed in Firefox 3.5 (or whatever they're calling it now). More fundamentally, calling fsync() from a GUI thread is literally asking for the GUI to be stalled until the data is on disk.