linux/mm.txt

大师兄

<previous description obsolete, deleted>
	Virtual memory map with 4 level page tables:
	0000000000000000 - 00007fffffffffff (=47 bits) user space, different per mm
	hole caused by [47:63] sign extension
	ffff800000000000 - ffff87ffffffffff (=43 bits) guard hole, reserved for hypervisor
	ffff880000000000 - ffffc7ffffffffff (=64 TB) direct mapping of all phys. memory
	ffffc80000000000 - ffffc8ffffffffff (=40 bits) hole
	ffffc90000000000 - ffffe8ffffffffff (=45 bits) vmalloc/ioremap space
	ffffe90000000000 - ffffe9ffffffffff (=40 bits) hole
	ffffea0000000000 - ffffeaffffffffff (=40 bits) virtual memory map (1TB)
	... unused hole ...
	ffffec0000000000 - fffffbffffffffff (=44 bits) kasan shadow memory (16TB)
	... unused hole ...
	ffffff0000000000 - ffffff7fffffffff (=39 bits) %esp fixup stacks
	... unused hole ...
	ffffffef00000000 - fffffffeffffffff (=64 GB) EFI region mapping space
	... unused hole ...
	ffffffff80000000 - ffffffff9fffffff (=512 MB)  kernel text mapping, from phys 0
	ffffffffa0000000 - ffffffffff5fffff (=1526 MB) module mapping space (variable)
	ffffffffff600000 - ffffffffffdfffff (=8 MB) vsyscalls
	ffffffffffe00000 - ffffffffffffffff (=2 MB) unused hole
	Virtual memory map with 5 level page tables:
	0000000000000000 - 00ffffffffffffff (=56 bits) user space, different per mm
	hole caused by [56:63] sign extension
	ff00000000000000 - ff0fffffffffffff (=52 bits) guard hole, reserved for hypervisor
	ff10000000000000 - ff8fffffffffffff (=55 bits) direct mapping of all phys. memory
	ff90000000000000 - ff91ffffffffffff (=49 bits) hole
	ff92000000000000 - ffd1ffffffffffff (=54 bits) vmalloc/ioremap space
	ffd2000000000000 - ffd3ffffffffffff (=49 bits) hole
	ffd4000000000000 - ffd5ffffffffffff (=49 bits) virtual memory map (512TB)
	... unused hole ...
	ffdf000000000000 - fffffc0000000000 (=53 bits) kasan shadow memory (8PB)
	... unused hole ...
	ffffff0000000000 - ffffff7fffffffff (=39 bits) %esp fixup stacks
	... unused hole ...
	ffffffef00000000 - fffffffeffffffff (=64 GB) EFI region mapping space
	... unused hole ...
	ffffffff80000000 - ffffffff9fffffff (=512 MB)  kernel text mapping, from phys 0
	ffffffffa0000000 - ffffffffff5fffff (=1526 MB) module mapping space
	ffffffffff600000 - ffffffffffdfffff (=8 MB) vsyscalls
	ffffffffffe00000 - ffffffffffffffff (=2 MB) unused hole
	Architecture defines a 64-bit virtual address. Implementations can support
	less. Currently supported are 48- and 57-bit virtual addresses. Bits 63
	through to the most-significant implemented bit are set to either all ones
	or all zero. This causes hole between user space and kernel addresses.
	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/PML5 pages of
	the processes using the page fault handler, with init_top_pgt as
	reference.
	Current X86-64 implementations support up to 46 bits of address space (64 TB),
	which is our current limit. This expands into MBZ space in the page tables.
	We map EFI runtime services in the 'efi_pgd' PGD in a 64Gb large virtual
	memory window (this size is arbitrary, it can be raised later if needed).
	The mappings are not part of any other kernel PGD and are only available
	during EFI runtime calls.
	The module mapping space size changes based on the CONFIG requirements for the
	following fixmap section.
	Note that if CONFIG_RANDOMIZE_MEMORY is enabled, the direct mapping of all
	physical memory, vmalloc/ioremap space and virtual memory map are randomized.
	Their order is preserved but their base will be offset early at boot time.
	-Andi Kleen, Jul 2004

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