Nice little performance improvement

[Mike Connell]

Hi,

> Interesting.  If you're not using incremental recursion (the default in
> rsync >= 3.0.0), I can see that the "du" would help by forcing the
> destination I/O to overlap the file-list building in time.  But with
> incremental recursion, the "du" shouldn't be necessary because rsync
> actually overlaps the checking of destination files with the file-list
> building on the source.
> 
Ignoring incremental recursion for a moment. It seems to me that anything
that can warm up the file cache before it is needed would be beneficial?