On Sat, Jul 30, 2011 at 03:25:32PM +0800, Coly Li wrote: > On 2011年07月29日 21:19, Joel Becker Wrote: > > On Fri, Jul 29, 2011 at 03:48:45AM -0600, Andreas Dilger wrote: > >> On 2011-07-28, at 4:07 PM, Joel Becker wrote: > >>> We use ethernet crc32 in ocfs2. btrfs uses crc32c. Frankly, I > >>> could have used crc32c if I'd really thought about the hardware > >>> acceleration benefits. I think it's a good idea for ext4. > >> > >> The problem with crc32[c] is that if you don't have hardware acceleration > >> it is terribly slow. > > > > We find ethernet crc32 just fine in ocfs2. I use the kernel's > > implementation, which survives everyone's network traffic, and of course > > we added the triggers to jbd2 so we only have to do the calculations on > > read and write. > > > > Ext4 supports non-journal mode, and there are a few users (Google, Taobao, etc.). > A trigger of jbd2 may not work well for non-journal Ext4 ... > > And in non-journal mode, there is not copy of any meta data block in jbd2, we need to be > more careful in check summing, e.g. inode/block bitmap blocks... Sure, but you could use a trigger in journaled mode and then do the checksums directly in the __ext4_handle_journal_dirty_*() functions in non-journaled mode. Sure, it would be a little more CPU time, but the user picked "checksums + no journal" at mkfs time. Joel -- Joel's Second Law: If a code change requires additional user setup, it is wrong. http://www.jlbec.org/ jlbec@xxxxxxxxxxxx -- 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
