COMP 3430 – Operating Systems
Virtual Memory 1
March 28th, 2022
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By the end of today’s lecture, you should be able to:
▶ Describe the concept of virtual memory. ▶ Describe how memory is or can be organized, physically and virtually.
The Woggle-Bug Book (Public Domain)
Poor me. (Pixabay License)
With your new team:
1. Introduce yourself !
2. Nominate someone to create a shared
space for taking notes .
3. Choose a team name (share in chat on
your return).
4. Answer the question: How much physical
memory is in your system?
Address spaces
A running program’s memory is (apparently) laid out in a certain way.
▶ Can we observe this?
▶ Let’s look at addresses.c.
▶ Let’s look at /proc/$PID/maps.
An address space (©RH & AC Arpaci-Dusseau)
Responsibilities
Based on what you do know about address spaces (and what you’ve learned in other courses like COMP 2280), who or what has the responsibility of managing the contents of:
1. The code segment? 2. The stack?
3. The heap?
Pixabay License
Managing the heap
Let’s try to experimentally determine if the OS manages the heap.
▶ Check out allocate.c.
▶ Use strace to see what system calls are
A heap. (Pixabay License)
▶ Memory has a certain layout from the perspective of a process.
▶ The OS enables this layout.
▶ … but maybe manages less than we originally thought.
▶ … or manages different parts than we originally thought.
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