Virtual Memory

Virtualization and virtual memory enable multiple processes to share a single set of hardware. Without hardware support for these software mechanisms, we wouldn’t have wide-spread computing today!

Virtualization

Before diving into the hardware and software mechanisms behind virtualization, I want to give a bit of motivation for virtualization generally.

This video talks about why we want virtualization and how processors are virtualized.

Virtual memory

This video introduces virtual memory and discusses segmentation as a mechanism to implement virtual memory.

Page-based virtual memory

This video goes back and talks about more motivation for virtual memory and introduces page-based virtual memory.

This video shows an example simple page table implementation: A flat page table.

Multi-level page tables

This video talks about the downsides of a flat page table and motivates a multi-level page table design.

This video discusses how the actual RISC-V and x86 page tables are implemented.

This videos extends the two-level page table for rv32 to 3 and 4 levels for rv64 and x86.

Performance and virtual memory

This video discusses how to access memory now that we’re using virtual address translation and the main performance overhead: walking the page table.

This video discusses a cache structure for virtual address translation: the TLB.

This video covers other virtual memory optimizations such as huge pages.

Virtual virtual memory

This section is optional and will not be on any quizzes or the exam. However, I think it’s important to talk about virtual machines and hypervisors as many of you will use these systems. Understanding how they work and how the hardware handles virtualization is key to getting good performance on the cloud or on VMs on your desktop.

This video discusses virtualization and its impacts on virtual memory and performance.

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