Fedora :: Jbd2_log_wait_commit Showing Huge Latency In LatencyTOP?

My large ext4 / filesystem seems to cause huge latency problems when writing a large file. For example, if I use split to break up a 40GB file into DVD-sized chunks, my browser becomes unresponsive, and it can take several seconds for Gnome terminal to respond to a mouse click.

I installed LatencyTOP, and it shows jbd2_log_wait_commit as the big offender, with Chrome waiting on that function for over 31000ms (or 31 seconds). I tried remounting / with barrier=0, but that didn't help. My hard drive is a WD20EARS-00MVWB0 2TB SATA disk. I recently switched my BIOS from IDE emulation to AHCI mode, but that didn't help. I tried running split with ionice, and that does help, but the system still isn't responsive as it should be, and I'd hate to have to remember to ionice every large write. Here is some relevant stuff from dmesg:

Code:

[ 1.294068] ata3: SATA link up 3.0 Gbps (SStatus 123 SControl 300)
[ 1.294096] ata2: SATA link up 3.0 Gbps (SStatus 123 SControl 300)
[ 1.294119] ata1: SATA link up 3.0 Gbps (SStatus 123 SControl 300)

[code]....

I'm running kernel version 2.6.38.8-35.fc15.x86_64.