XFS hung on 2.6.33.3 kernel

[Dave Chinner]

On Thu, Aug 05, 2010 at 02:42:38AM -0400, Ilia Mirkin wrote:
> On Thu, Aug 5, 2010 at 2:25 AM, Dave Chinner <david at fromorbit.com> wrote:
> > a couple of things to see if the hang can be caused faster? Maybe
> > trying these different initial conditions:
> 
> Together or independently?

independently first - then if that does't work, maybe together?

> >        - allocate the file with worst case fragmentation by
> >          writing it backwards in synchronous 4k blocks before
> >          running the test
> 
> I created the file with
> 
> dd if=/dev/zero of=... bs=1M count=...
> 
> How would I "write backwards"? Like truncate and then seek to the end,
> write, seek back, write, etc? Is there a utility that might do it
> already?

For a 1GB file:

$ for i in `seq 256000 1 0`; do
> dd if=/dev/zero of=testfile bs=4k count=1 seek=$i conv=notrunc,sync
> done

Cheers,

Dave.
-- 
Dave Chinner
david at fromorbit.com