It seems that there must be at least one node in mems and at least one CPU
in cpus in order to be able to assign tasks to a cpuset.  This makes sense.
 And I think it would also make sense to include a mems setting in the
basic usage section of the documentation.

I also wonder if something logged to dmsg, explaining why a write failed,
would be a good enhancement.  I ended up having rummage arround in cpuset.c
in order to work out why my configuration was failing.
Signed-off-by: Simon Horman <horms@verge.net.au>
Acked-by: Paul Jackson <pj@sgi.com>
Cc: Paul Menage <menage@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>