Videos: Virtual Memory

Virtual memory allows a process-specific view of memory, using physical memory as a cache for disk, enforcing write and execution constraints, and efficiently forking processes.

• Virtual Memory 1: Virtual and physical addresses   2:44
  How virtual memory allows a parent and child process to have different views of the same addresses—by having a configurable mapping from virtual addresses to physical addresses.

• Virtual Memory 2: Linux process layout   2:16
  The organization of (virtual) memory that a Linux process uses.

• Virtual Memory 3: Memory as a cache for disk   2:59
  Virtual memory allows a process to use more virtual memory than is available in phsyical form. In that mode, physical memory acts as a kind of cache for data stored on disk.

• Virtual memory 4: Address translation   4:06
  How a virtual memory table supports the translation of a virtual address to a phsyical address.

• Virtual memory 5: Page hits, page faults, and the TLB   3:56
  A view of address translation at the level of CPU, memory, and disk interactions, and how a TLB acts as a specialized cache for translation.

• Virtual memory 6: Mapped, writable, and executable pages   4:05
  A virtual-memory system can also check write and execute permissions to help detect and prevent errors.

• Virtual memory 7: Demonstrating page permissions   2:35
  An example program that demonstrates write and execute permissions for different kinds of memory, especially as specified in an ELF executable.

• Virtual memory 8: mmap   4:28
  The mmap syscall allows a program to manipulate the virtual-memory mapping.

• Virtual memory 8b: munmap   1:43
  The munmap system call removes page mappings previously created with map.

• Virtual memory 9: mprotect and SIGSEGV   3.23
  The mprotect system supports modifying the execute and write permissions of a mapped page. Permission violations can be handled through the SIGSEGV signal—for example by changing page permissions via mprotect.

• Virtual memory 10: Shared libraries   2:12
  How virtual memory enables in-memory sharing of position-independent code for a shared library.

• Virtual memory 11: fork, copy-on-write, and MAP_SHARED   3:28
  The fork syscall efficiently implements as process “copy” by sharing pages and copying shared pages when they’re written to. A program can enable sharing between a parent process and a child by creating a page with the MAP_SHARED option.