Why is the page size of Linux (x86) 4 KB, how is that calculated?

Question

The default memory page size of the Linux kernel on x86 architecture was 4 KB, I wonder how was that calculated, and why ?

Answer 1

The default page size is fixed by what the MMU (memory management unit) of the CPU supports. In 32-bit protected mode x86 supports two kinds of pages:

• normal ones, 4 KiB
• huge ones, 4 MiB

Not all x86 processors support large pages. One needs to have a CPU with Page Size Extension (PSE) capabilities. This excludes pre-Pentium processors. Virtually all current-generation x86 CPUs implements it.

4 KiB is widely popuplar page granularity in other architectures too. One could argue that this size comes from the division of a 32-bit virutal address into two 10-bit indexes in page directories/tables and the remaining 12 bits give the 4 KiB page size.