linux/Documentation/x86_64/mm.txt
Linus Torvalds 1da177e4c3 Linux-2.6.12-rc2
Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!
2005-04-16 15:20:36 -07:00

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<previous description obsolete, deleted>
Virtual memory map with 4 level page tables:
0000000000000000 - 00007fffffffffff (=47bits) user space, different per mm
hole caused by [48:63] sign extension
ffff800000000000 - ffff80ffffffffff (=40bits) guard hole
ffff810000000000 - ffffc0ffffffffff (=46bits) direct mapping of phys. memory
ffffc10000000000 - ffffc1ffffffffff (=40bits) hole
ffffc20000000000 - ffffe1ffffffffff (=45bits) vmalloc/ioremap space
... unused hole ...
ffffffff80000000 - ffffffff82800000 (=40MB) kernel text mapping, from phys 0
... unused hole ...
ffffffff88000000 - fffffffffff00000 (=1919MB) module mapping space
vmalloc space is lazily synchronized into the different PML4 pages of
the processes using the page fault handler, with init_level4_pgt as
reference.
Current X86-64 implementations only support 40 bit of address space,
but we support upto 46bits. This expands into MBZ space in the page tables.
-Andi Kleen, Jul 2004