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SubjectRe: [Lse-tech] Re: 10.31 second kernel compile
   From: Paul Mackerras <>
Date: Sat, 16 Mar 2002 22:55:40 +1100 (EST)

IMHO it would be interesting to compare the size and complexity of
using a hash table for the page tables with a 5-level tree. For a
32-bit address space I think the tree wins hands down but for a full
64-bit address space I am not convinced either way at present.

You only need a 4-level tree for a full 64-bit address space as long
as you can guarentee less than (32 + PAGE_SHIFT) bits of physical
addressing (ie. you can use 32-bit pmd_t's and pgd_t's in that case).

At least this is how I remember the numbers working out.
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