I had the same problem with memory resources. I have an ADM 64 Opteron with 1GB RAM. After 1 week the memory is 95% and if it reaches 99% then i can not make or receive calls. The solution i have found is:
Sorry about that, my mistake. So let's clarrify this.
To free pagecache:
echo 1 > /proc/sys/vm/drop_caches
To free dentries and inodes:
echo 2 > /proc/sys/vm/drop_caches
To free pagecache, dentries and inodes:
echo 3 > /proc/sys/vm/drop_caches
You don't have to run all of them, just the option that you want to clean. I use the echo 3.
I did it through webmin but you can add it manually in /var/spool/cron/root.
if you want to do it manually just add to the above file one of the below: