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Commit 975b3d3d authored by Mark Lord's avatar Mark Lord Committed by Linus Torvalds
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[PATCH] VMSPLIT config options 



Enable selection of different user/kernel VM splits for i386, including an
optimized mode for 1GB physical RAM, which gives the kernel a direct (non
HIGHMEM) mapping to the entire 1GB rather than just the first 896MB.

There is a similarly a similarly optimized mode for machines with exactly 2GB
of physical RAM.

This can speed up the kernel by avoiding having to create/destroy temporary
HIGHMEM mappings, and by not having to include HIGHMEM support at all on such
machines.  The flip side is that there's less virtual addressing left for
userspace in these alternatives, and some binary-only kernel modules may
misbehave unless rebuilt with the same VMSPLIT option as the main kernel
image.

Original idea/patch from Jens Axboe, modified based on suggestions from Linus
et al.

Signed-off-by: default avatarMark Lord <mlord@pobox.com>
Signed-off-by: default avatarJens Axboe <axboe@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 4940fb44

arch/i386/Kconfig

+37 −0
Original line number Diff line number Diff line
@@ -448,6 +448,43 @@ config HIGHMEM64G 


endchoice



choice

	depends on EXPERIMENTAL && !X86_PAE

	prompt "Memory split"

	default VMSPLIT_3G

	help

	  Select the desired split between kernel and user memory.



	  If the address range available to the kernel is less than the

	  physical memory installed, the remaining memory will be available

	  as "high memory". Accessing high memory is a little more costly

	  than low memory, as it needs to be mapped into the kernel first.

	  Note that increasing the kernel address space limits the range

	  available to user programs, making the address space there

	  tighter.  Selecting anything other than the default 3G/1G split

	  will also likely make your kernel incompatible with binary-only

	  kernel modules.



	  If you are not absolutely sure what you are doing, leave this

	  option alone!



	config VMSPLIT_3G

		bool "3G/1G user/kernel split"

	config VMSPLIT_3G_OPT

		bool "3G/1G user/kernel split (for full 1G low memory)"

	config VMSPLIT_2G

		bool "2G/2G user/kernel split"

	config VMSPLIT_1G

		bool "1G/3G user/kernel split"

endchoice



config PAGE_OFFSET

	hex

	default 0xB0000000 if VMSPLIT_3G_OPT

	default 0x78000000 if VMSPLIT_2G

	default 0x40000000 if VMSPLIT_1G

	default 0xC0000000



config HIGHMEM

	bool

	depends on HIGHMEM64G || HIGHMEM4G

include/asm-i386/page.h

+2 −2
Original line number Diff line number Diff line
@@ -110,10 +110,10 @@ extern int page_is_ram(unsigned long pagenr); 
#endif /* __ASSEMBLY__ */



#ifdef __ASSEMBLY__

#define __PAGE_OFFSET		(0xC0000000)

#define __PAGE_OFFSET		CONFIG_PAGE_OFFSET

#define __PHYSICAL_START	CONFIG_PHYSICAL_START

#else

#define __PAGE_OFFSET		(0xC0000000UL)

#define __PAGE_OFFSET		((unsigned long)CONFIG_PAGE_OFFSET)

#define __PHYSICAL_START	((unsigned long)CONFIG_PHYSICAL_START)

#endif

#define __KERNEL_START		(__PAGE_OFFSET + __PHYSICAL_START)