求助：mysql狂吃内存，怎么办？

我的论坛系统，centos5+mysql4.0.26+php4.4,数据库大小2G，60分钟在线人数2400。我的服务器内存是2G，现在一开MYSQL，内存占用就到了1.9G,我很担心它会当掉，请问这个占用正常吗？？

我的MY.CNF配置：
[client]
#password = your_password
port = 3306
socket = /tmp/mysql.sock
#socket = /var/lib/mysql/mysql.sock
# Here follows entries for some specific programs

# The MySQL server
[mysqld]
port = 3306
socket = /tmp/mysql.sock
#socket = /var/lib/mysql/mysql.sock
skip-locking
key_buffer = 128M
max_allowed_packet = 1M
table_cache = 256
sort_buffer_size = 1M
net_buffer_length = 16K
myisam_sort_buffer_size = 1M
max_connections=120
#addnew config
wait_timeout =120
back_log=100
read_buffer_size = 1M
thread_cache=32

我也出现了这样的情况,一开mysql内存就猛涨200M,比去年的股票涨得还快