- use a hash rather than SPLAY trees.
SPLAY tree is a wrong algorithm to use here.
will be revisited if it slows down anything other than
micro-benchmarks.
- optimize the single mapping case (it's a common case) by
embedding an entry into mdpage.
- don't keep a pmap pointer as it can be obtained from ptp.
(discussed on port-i386 some years ago.)
ideally, a single paddr_t should be enough to describe a pte.
but it needs some more thoughts as it can increase computational
costs.
- pmap_enter: simplify and fix races with pmap_sync_pv.
- don't bother to lock pm_obj[i] where i > 0, unless DIAGNOSTIC.
- kill mp_link to save space.
- add many KASSERTs.
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