Turn off write barriers on ext4 whiche FS is mounted

I am doing some IO intensive DB imports that run for several days now and the IO performance has dropped tremendously over times. The DB data files (log files) are on an ext4 formatted logical volume which is mounted with default options (did not specify something special in fstab). Since I just learned that ext4 enables write barriers by default: Q: Is there some way to disable write barriers online (i.e. while the file system is in use), because I cannot interrupt the import and don't want to restart it again. I am aware that

• write barriers might not be the only thing impeding performance
• it is a bad idea to have write barriers disabled on journalling file systems if data safty is important (e.g. on a production system)