4.8 ffs_dirpref problem

[Doug White]

Purge extensive cc:.

On Tue, 21 Oct 2003, Ken Marx wrote:

> We have 560GB raids that were sometimes bogging down heavily
> in our production systems. Under 4.8-RELEASE (recently upgrated from 4.4)
> we find that when:
>
> 	o the raid file system grows to over 85% capacity (with only
> 	  30% inode usage)
> 	o we create ~1500 or so 2-6kb files in a given dir
> 	o (note: soft updates NOT enabled)

Interesting problems and analysis.

If I'm reading the diffs and source right, the old allocation algorithm
exists at the end of the dirpref function, below the comment about the
backstop.  It would be interesting to wrap the rest of the function in a
tunable so you could easily short-circuit to the backstop.

I don't know if it could be done on a per-filesystem basis. You might just
have to eat the old layout semantics for the entire system if we want to
keep the cost of the tunable low.

-- 
Doug White                    |  FreeBSD: The Power to Serve
dwhite at gumbysoft.com          |  www.FreeBSD.org