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Why are pages 4KiB anyways?
There is a trade-off between memory wasted in:
  • page tables
  • extra padding memory within pages
This can be seen with the extreme cases:
  • if the page size were 1 byte:
    • granularity would be great, and the OS would never have to allocate unneeded padding memory
    • but the page table would have 2^32 entries, and take up the entire memory!
  • if the page size were 4GiB:
    • we would need to swap 4GiB to disk every time a new process becomes active
    • the page size would be a single entry, so it would take almost no memory at all
x86 designers have found that 4KiB pages are a good middle ground.