CPU load too small but RAM overload

21221mysql288324 kB/usr/sbin/mysqld --basedir=/ --datadir=/var/lib/mysql --user=mysql --pid-file=/v ... 21222mysql288324 kB/usr/sbin/mysqld --basedir=/ --datadir=/var/lib/mysql --user=mysql --pid-file=/v ... 21223mysql288324 kB/usr/sbin/mysqld --basedir=/ --datadir=/var/lib/mysql --user=mysql --pid-file=/v ... 21373mysql288324 kB/usr/sbin/mysqld --basedir=/ --datadir=/var/lib/mysql --user=mysql --pid-file=/v ... 21398mysql288324 kB/usr/sbin/mysqld --basedir=/ --datadir=/var/lib/mysql --user=mysql --pid-file=/v ... 21403mysql288324 kB/usr/sbin/mysqld --basedir=/ --datadir=/var/lib/mysql --user=mysql --pid-file=/v ... 21450mysql288324 kB/usr/sbin/mysqld --basedir=/ --datadir=/var/lib/mysql --user=mysql --pid-file=/v ... 21451mysql288324 kB/usr/sbin/mysqld --basedir=/ --datadir=/var/lib/mysql --user=mysql --pid-file=/v ... 21482mysql288324 kB/usr/sbin/mysqld --basedir=/ --datadir=/var/lib/mysql --user=mysql --pid-file=/v ... 21541mysql288324 kB/usr/sbin/mysqld --basedir=/ --datadir=/var/lib/mysql --user=mysql --pid-file=/v ... 21546mysql288324 kB/usr/sbin/mysqld --basedir=/ --datadir=/var/lib/mysql --user=mysql --pid-file=/v ... 21549mysql288324 kB/usr/sbin/mysqld --basedir=/ --datadir=/var/lib/mysql --user=mysql --pid-file=/v ... 22193mysql288324 kB/usr/sbin/mysqld --basedir=/ --datadir=/var/lib/mysql --user=mysql --pid-file=/v ... 22543mysql288324 kB/usr/sbin/mysqld --basedir=/ --datadir=/var/lib/mysql --user=mysql --pid-file=/v ... 22963mysql288324 kB/usr/sbin/mysqld --basedir=/ --datadir=/var/lib/mysql --user=mysql --pid-file=/v ... 23122mysql288324 kB/usr/sbin/mysqld --basedir=/ --datadir=/var/lib/mysql --user=mysql --pid-file=/v ...

[mysqld]
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
skip-locking
skip-innodb
query_cache_limit=8M
query_cache_size=256M
query_cache_type=1
max_connections=500
max_user_connections=10
interactive_timeout=20
wait_timeout=20
connect_timeout=6
thread_cache_size=128
key_buffer=16M
join_buffer=1M
max_allowed_packet=16M
table_cache=1024
record_buffer=1M
sort_buffer_size=2M
read_buffer_size=2M
max_connect_errors=10
# Try number of CPU's*2 for thread_concurrency
thread_concurrency=4
myisam_sort_buffer_size=64M
#log-bin
server-id=1
[mysql.server]
user=mysql
basedir=/var/lib
[safe_mysqld]
err-log=/var/log/mysqld.log
pid-file=/var/lib/mysql/mysql.pid
open_files_limit=8192
[mysqldump]
quick
max_allowed_packet=16M
[mysql]
no-auto-rehash
#safe-updates
[isamchk]
key_buffer=32M
sort_buffer=32M
read_buffer=16M
write_buffer=16M
[myisamchk]
key_buffer=32M
sort_buffer=32M
read_buffer=16M
write_buffer=16M