https://bugzilla.kernel.org/show_bug.cgi?id=42895 --- Comment #15 from Theodore Tso <tytso@xxxxxxx> 2012-05-16 20:24:41 --- Eugene, one thing which may not be obvious is that it's not the number of disk blocks that are written; it's how often the disk drive seeks, and more importantly, wakes up. Once you wake up the hard drive, and the hard drive has positioned the hard drive heads to the right place on disk, whether you write 8k or 32k or 128k doesn't make that much difference in terms of time and power requirements. So for example, if gedit writes a single file, it might cause multiple jbd2 writes: for the block allocation bitmap, for the inode allocation bitmap, the inode table, the block group summary block, and then the data block itself. But the jbd2 writes are contiguous, and happen all at once, during a journal commit (which is caused either by an explicit fsync or by the 5 second commit timer which starts a journal commit 5 seconds after metadata changes have been applied to the file system). So you might see "lots of jbd2 writes", but it's misleading in terms of the power requirements or disk time fraction consumed by the journalling. Of course, if you don't care about consistency after a crash, you can always disable journalling. But then you might lose data files after a system crash. The bottom line is that if you want to keep the disk sleeping for longer, you have to be absolutely firm about not having programs write to the file system. For things like gedit, it's caused by user activity, and that's fine and good. But if NetworkManager is dirtying the disk every few seconds or minutes, especially if it's something useless like some kind of timestamp file, it's a bug that should be filed with extreme prejudice against NetworkManager, since it's guaranteed to be constantly waking up the disk. -- Configure bugmail: https://bugzilla.kernel.org/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- You are watching the assignee of the bug. -- 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
