"Too many open files" are opened by nova-compute

1. nova-comp open too many files about 1112. (but the output of "ulimit -n" just is 1024)

2. nova-comp open too many files inode 3641 /lib/modules/2.6.32-279.el6.x86_64/kernel/net/sunrpc/auth_gss/rpcsec_gss_krb5.ko

nova-comp 20916 28u REG 0,9 0 3641 anon_inode
nova-comp 20916 29u REG 0,9 0 3641 anon_inode
...

nova-comp 20975 22u REG 0,9 0 3641 anon_inode
nova-comp 20975 23u REG 0,9 0 3641 anon_inode
...

---------------------------
[test@Openstack_Grizzly_ControlNode ~]$ ps -ef | grep nova
test 10374 10357 0 04:54 pts/1 00:00:00 grep nova
test 11292 11272 0 Dec04 pts/7 00:00:01 python /home/.../nova/bin/nova-api
test 11300 11292 0 Dec04 pts/7 00:00:01 python /home/.../nova/bin/nova-api
test 11303 11292 0 Dec04 pts/7 00:00:50 python /home/.../nova/bin/nova-api
test 11304 11292 0 Dec04 pts/7 00:00:01 python /home/.../nova/bin/nova-api
test 11479 11373 0 Dec04 pts/9 01:21:03 python /home/.../nova/bin/nova-network
test 11650 11485 0 Dec04 pts/10 00:39:28 python /home/.../nova/bin/nova-scheduler
nobody 13152 1 0 Dec04 ? 00:02:29 /usr/sbin/dnsmasq --strict-order --bind-interfaces --conf-file= --domain=novalocal --pid-file=/home/.../data/nova/networks/nova-br100.pid --listen-address=10.0.1.1 --except-interface=lo --dhcp-range=set:'private',10.0.1.2,static,120s --dhcp-lease-max=256 --dhcp-hostsfile=/home/.../data/nova/networks/nova-br100.conf --dhcp-script=/home/.../nova/bin/nova-dhcpbridge --leasefile-ro
root 13153 13152 0 Dec04 ? 00:00:00 /usr/sbin/dnsmasq --strict-order --bind-interfaces --conf-file= --domain=novalocal --pid-file=/home/.../data/nova/networks/nova-br100.pid --listen-address=10.0.1.1 --except-interface=lo --dhcp-range=set:'private',10.0.1.2,static,120s --dhcp-lease-max=256 --dhcp-hostsfile=/home/.../data/nova/networks/nova-br100.conf --dhcp-script=/home/.../nova/bin/nova-dhcpbridge --leasefile-ro
test 20916 1 0 Dec05 ? 01:25:35 /usr/bin/python /usr/bin/nova-compute
test 20975 1 0 Dec05 ? 01:24:55 /usr/bin/python /usr/bin/nova-compute --config-file=/etc/nova/nova2.conf
[test@Openstack_Grizzly_ControlNode ~]$
[test@Openstack_Grizzly_ControlNode ~]$ ulimit -n
1024
[test@Openstack_Grizzly_ControlNode ~]$ lsof -p 20916 | wc -l
1112
[test@Openstack_Grizzly_ControlNode ~]$ lsof -p 20975 | wc -l
1112
[test@Openstack_Grizzly_ControlNode ~]$ lsof -p 20975 | grep 3641 | wc -l
1009
[test@Openstack_Grizzly_ControlNode ~]$ lsof -p 20916 | grep 3641 | wc -l
1009
[test@Openstack_Grizzly_ControlNode ~]$
[test@Openstack_Grizzly_ControlNode ~]$ ulimit -a
core file size (blocks, -c) 0
data seg size (kbytes, -d) unlimited
scheduling priority (-e) 0
file size (blocks, -f) unlimited
pending signals (-i) 14874
max locked memory (kbytes, -l) 64
max memory size (kbytes, -m) unlimited
open files (-n) 1024
pipe size (512 bytes, -p) 8
POSIX message queues (bytes, -q) 819200
real-time priority (-r) 0
stack size (kbytes, -s) 10240
cpu time (seconds, -t) unlimited
max user processes (-u) 1024
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited
[test@Openstack_Grizzly_ControlNode ~]$
[test@Openstack_Grizzly_ControlNode ~]$ ls -li /lib/modules/2.6.32-279.el6.x86_64/kernel/net/sunrpc/auth_gss/rpcsec_gss_krb5.ko
3641 -rwxr--r--. 1 root root 49576 Jun 14 2012 /lib/modules/2.6.32-279.el6.x86_64/kernel/net/sunrpc/auth_gss/rpcsec_gss_krb5.ko
[test@Openstack_Grizzly_ControlNode ~]$

nova-compute.log:
2012-12-13 22:31:21 20916 ERROR nova.virt.powervm.common [-] Error while trying to connect: Error reading SSH protocol banner[Errno 24] Too many open files
2012-12-13 22:31:21 20916 TRACE nova.virt.powervm.common Traceback (most recent call last):
2012-12-13 22:31:21 20916 TRACE nova.virt.powervmt.common File "/home/.../nova/nova/virt/powervm/common.py", line 60, in ssh_connect
2012-12-13 22:31:21 20916 TRACE nova.virt.powervm.common port=port)
2012-12-13 22:31:21 20916 TRACE nova.virt.powervm.common File "/usr/lib/python2.6/site-packages/paramiko/client.py", line 295, in connect
2012-12-13 22:31:21 20916 TRACE nova.virt.powervm.common t.start_client()
2012-12-13 22:31:21 20916 TRACE nova.virt.powervm.common File "/usr/lib/python2.6/site-packages/paramiko/transport.py", line 451, in start_client
2012-12-13 22:31:21 20916 TRACE nova.virt.powervm.common raise e
2012-12-13 22:31:21 20916 TRACE nova.virt.powervm.common SSHException: Error reading SSH protocol banner[Errno 24] Too many open files
2012-12-13 22:31:21 20916 TRACE nova.virt.powervm.common