Managing Virtual Memory

<aside> 💡 Consider that we are creating a software that basically manages the shell for us, in this case, when the shell runs a process, we want to fork so that the process can run in a separate address space and then execute, without terminating the shell parent process

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The Downfalls of Physical Memory

• the benefits is that it is simple for hardware
• these tactics are used in embedded microcontrollers but is genuinely not used largely due to the following reasons
  • fragmentation → a lot of different programs use different amounts of memory and it is hard to allocate all of the memory equally when these numbers are constantly changing
  • no solution when we are out of memory
  • lots of burden to figure out what the memory limitations are

Strategy of Using Virtual Memory

• the cpu passes the virtual memory address through the memory management unit which then converts into the physical address within the memory
• It makes distinguishing addresses from different processes easier
• paging logically divides the memory into chunks that are called pages
• any virtual page can be mapped to any physical page → that is fully associated
• translating VA to PA before accessing cache is done bc it makes distinguishing addresses from different processes easier
• WHENEVER YOU PRINT ADDRESS, IT IS VIRTUAL
  • this occurs because all of the translations are for the virtual address and each process does not “own” a physical memory location

Benefits of Virtual Memory

• allows for isolating address spaces for different process
• it allows the address space to be larger than the physical address space
• Multi-level allows for less bits to the block offset due to using another thing for indexing into the level
• uses both spatial and prime locality

Pages

• Page size is 0x1000 bytes = 2^12