InnoDB Buffer gets to 100% and doesn't go down (no replies)

hi,

I have thew following configuration on a 64-bits machine with 32GB of RAM and handling a database of 120GB approx. and increasing...

innodb_buffer_pool_size = 18G

Some other parameters info:

wait_timeout = 3600
innodb_lock_wait_timeout=300


key_buffer = 16M
max_allowed_packet = 16M
thread_stack = 192K
thread_cache_size = 8


query_cache_limit = 1M
query_cache_size = 32M




The thing is that after some time running the server buffer reaches 100% of usage and doesn't go down.

Any hint about this?

Thanks in advance