Who is leaking memory in my Linux Jessie/KDE4 installation?

[Omer Zak]

I have a 8GB PC which runs Linux Debian Jessie with KDE 4.4.
My problem is to find out who is occupying almost 4GB memory some time
after rebooting, even when nothing heavy is running.

The heaviest applications that I run are:
- A VirtualBox virtual machine occupying 3GB memory
- Google Chrome browser (version 37.0.2062.94, 64-bit)
- Evolution 3.12.2.

However, even when they are closed, a lot memory is still reported to be
in use.

My question is: besides top, what tools can be used to find who is using
all this memory?
The next question, of course, is how to get rid of those memory hogs
without destabilizing the system.

--- Omer

-- 
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