[deliverable/linux.git] / Documentation / x86_64 / mm.txt


<previous description obsolete, deleted>

Virtual memory map with 4 level page tables:

0000000000000000 - 00007fffffffffff (=47 bits) user space, different per mm
hole caused by [48:63] sign extension
ffff800000000000 - ffff80ffffffffff (=40 bits) guard hole
ffff810000000000 - ffffc0ffffffffff (=46 bits) direct mapping of all phys. memory
ffffc10000000000 - ffffc1ffffffffff (=40 bits) hole
ffffc20000000000 - ffffe1ffffffffff (=45 bits) vmalloc/ioremap space
ffffe20000000000 - ffffe2ffffffffff (=40 bits) virtual memory map (1TB)
... unused hole ...
ffffffff80000000 - ffffffff82800000 (=40 MB)   kernel text mapping, from phys 0
... unused hole ...
ffffffff88000000 - fffffffffff00000 (=1919 MB) module mapping space

The direct mapping covers all memory in the system up to the highest
memory address (this means in some cases it can also include PCI memory
holes).

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 bits of address space,
but we support up to 46 bits. This expands into MBZ space in the page tables.

-Andi Kleen, Jul 2004
Commit	Line	Data
1da177e4 LT	1
	2	<previous description obsolete, deleted>
	3
	4	Virtual memory map with 4 level page tables:
	5
57d30772	6	0000000000000000 - 00007fffffffffff (=47 bits) user space, different per mm
1da177e4	7	hole caused by [48:63] sign extension
57d30772 RD	8	ffff800000000000 - ffff80ffffffffff (=40 bits) guard hole
	9	ffff810000000000 - ffffc0ffffffffff (=46 bits) direct mapping of all phys. memory
	10	ffffc10000000000 - ffffc1ffffffffff (=40 bits) hole
	11	ffffc20000000000 - ffffe1ffffffffff (=45 bits) vmalloc/ioremap space
0889eba5	12	ffffe20000000000 - ffffe2ffffffffff (=40 bits) virtual memory map (1TB)
1da177e4	13	... unused hole ...
57d30772	14	ffffffff80000000 - ffffffff82800000 (=40 MB) kernel text mapping, from phys 0
1da177e4	15	... unused hole ...
57d30772	16	ffffffff88000000 - fffffffffff00000 (=1919 MB) module mapping space
1da177e4	17
57d30772	18	The direct mapping covers all memory in the system up to the highest
8315eca2	19	memory address (this means in some cases it can also include PCI memory
57d30772	20	holes).
8315eca2	21
1da177e4 LT	22	vmalloc space is lazily synchronized into the different PML4 pages of
	23	the processes using the page fault handler, with init_level4_pgt as
	24	reference.
	25
57d30772 RD	26	Current X86-64 implementations only support 40 bits of address space,
57d30772 RD	27	but we support up to 46 bits. This expands into MBZ space in the page tables.
1da177e4 LT	28
1da177e4 LT	29	-Andi Kleen, Jul 2004