On Fri, Aug 24, 2012 at 12:43:28PM -0600, Josef Bacik wrote:

                Original        Patched
SATA drive      82KB/s          140KB/s
Fusion drive    431KB/s         2532KB/s

So around 2-6 times faster depending on your hardware.  There are a few
corner cases, for example if you truncate at all we have to do it the old
way since there is no way to be sure what is in the log is ok.  This
probably could be done smarter, but if you write-fsync-truncate-write-fsync
you deserve what you get.  All this work is in RAM of course so if your
inode gets evicted from cache and you read it in and fsync it we'll do it
the slow way if we are still in the same transaction that we last modified
the inode in.

I think I sent Liubo down the wrong path on this one, and Josef and I
banged out some ideas for a different (hopefully less complex) way to
solve the problem.  Josef, these results look fantastic.

-chris