Re: [PATCH] Btrfs: turbo charge fsync

[Chris Mason <chris.mason@fusionio.com>]

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