Tracking down memory leaks

[Marc Shapiro]

Is there a way to determine what is using up my memory?  I have an 8GB 
system and every few days the memory usage rises to over 7 GB and up to 
a GB, or more of swap is used.  Granted, I have 3 X sessions running, 
along with 2 instances of Firefox and one of Chrome, not to mention up 
to 3 instances of Libre Office, but... When I first added the 8 GB (I 
used to do this on 2.25 GB!) I could run for months without having a 
memory problem.  Now it's every few days.

When this happens, I exit all programs and shut down all three X 
sessions.  I also log out the other two users.  This leaves me with only 
a single login and nothing but bash running.  When I run 'free' it 
usually shows over 2 GB in use!  When I reboot, the memory usage is back 
down at about 250 MB.  Much more reasonable.

So how do I tell what is using up the memory and not freeing it up? Is 
there a way to free that memory without having to reboot?

Marc