zfs on ubuntu locks up if you overcommit arc

Hey just a quick note.. be careful what you ask for.
(this applies to the zfsonlinux kernel mode zfs, not the fuse variety)
From a couple different servers, it seems you need to leave (at a rough guess) 4GB of memory free for ubuntu or your zpool scrub can hang your system if you manually set your zfs_arc_max parameter too high.

Safe config (has been working for me anyway) for a 10GB VM:

root@ubuntuzfs03:~# ~/zfs_show.sh
config
---------------------
options zfs zfs_arc_max=6000000000 zfs_arc_meta_limit=4900000000 zfs_arc_min=5900000000



runtime values
---------------------
c_min                           4    5900000000
c_max                           4    6000000000
size                            4    43729016
hdr_size                        4    1011296
data_size                       4    41999872
other_size                      4    717848
anon_size                       4    16384
mru_size                        4    14393344
mru_ghost_size                  4    0
mfu_size                        4    27590144
mfu_ghost_size                  4    16384
l2_size                         4    0
l2_hdr_size                     4    0
duplicate_buffers_size          4    0
arc_no_grow                     4    0
arc_tempreserve                 4    0
arc_loaned_bytes                4    0
arc_prune                       4    0
arc_meta_used                   4    36782200
arc_meta_limit                  4    4900000000
arc_meta_max                    4    36782200
root@ubuntuzfs03:~#

I was running with 8GB of ARC and my zpool scrub was crashing. Anyway, just wanted to share, as its not obvious why the zpool scrub was locking up the system, but it seems to be something to do with the kernel not being able to allocate memory.