Our powerfail testing turned up an odd regression when using fsync() in no-journal mode to force data to the device. We saw loss rates (both file and data) that were much higher than the same test using ext2 (60+% loss versus <10%). We've done some investigation and one thing that stood out was that in the no-journal case, ext4_sync_file() was just calling sync_inode() (and nothing else), while ext2_sync_file(), for comparison, was also calling sync_mapping_buffers() to actually push the data out. I therefore hacked ext4_sync_file() to call sync_mapping_buffers() in the no-journal case; when we reran the test we saw that the loss rate dropped from 60+% to around 50%. While it's clear that we have more work to do in this area, this is a significant improvement. It appears that this was just missed when we did the no-journal work. Do you guys concur? The other interesting bit of this is that ext4 no-journal without using fsync() has, apparently, basically the same loss rate as ext2 with fsync(). -- Frank Mayhar <fmayhar@xxxxxxxxxx> Google, Inc. -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
