Question : How to sumarize RAM (memory) used by process?

My server is Centos, running apache, php, mysql ....

When running, it increase memory much
Server has 8G RAM, and memory increase 1500MB, 1600MB .... to 8000MB

How can I check what process use much memory? What caused my problem?

Thank you!

Answer : How to sumarize RAM (memory) used by process?

Use the following command lines:
top
ps -eo pmem,pcpu,rss,vsize,args | sort -k 1 -r | more