[CentOS] centos + kswapd0 error

Hi all

I have a box with Centos 4 and qmail with all pathches. since Last month i
have had twice the same problem. The process kswapd0 uses all my resources
of CPU and RAM memory and the consequence is that my local queue grow up and
the box go slow too.

The first time i guess the problem was the version of the kernel, so i did
an upgrade form kernel.i686 2.6.9-5.0.3.EL to kernel.i686 2.6.9-5.0.5.EL

apparently the problem was solved but today the problem came again. The
following snapshot shows the situation:


top - 10:53:48 up 16 days, 20:05,  1 user,  load average: 119.27, 116.16,
114.33
Tasks: 528 total,  13 running, 515 sleeping,   0 stopped,   0 zombie
Cpu(s):  5.4% us, 89.4% sy,  0.0% ni,  0.3% id,  4.8% wa,  0.0% hi,  0.1% si
Mem:   2075012k total,  2073404k used,     1608k free,    71056k buffers
Swap:  4192924k total,  4192924k used,        0k free,    36380k cached

PID    USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+     COMMAND
60     root      17   0     0    0    0 D 75.4  0.0   585:22.79  kswapd0
2164   root      15   0  1736  484  432 S 31.0  0.0   31:57.07   couriertcpd
16334  vpopmail  19   0  2660  804  668 R 24.7  0.0   0:01.69    imapd
2158   root      15   0  3264  488  432 S 23.4  0.0   1:17.51    couriertcpd
32608  apache    16   0 21604 8440 3016 R 15.5  0.4   1:38.09    httpd
15284  vpopmail  18   0  4384 1032  760 R 14.9  0.0   0:08.32
vdelivermail



I really do not know what thing should i do for solve this problem

thanks in advance

Mario