- Map in all physical memory first in system space. This reduces
pmap_copy_page() and pmap_zero_page to 3 resp. 2 instructions.
- Have fized position user page tables. Makes the pv_table smaller
and all reverse references faster (and simpler).
- Remove the wiring code. Nobody doesn't even know what a DR32 is anymore.
- Simulate page reference bit by setting page invalid, as suggested by
Rich Draves in a paper for 1991 Mach Usenix Symposium.
This reduced the time spent in the pmap module to between 70-75% of
the previous; and made process startup _much_ faster.
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