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authorMark Lord <lkml@rtr.ca>2006-02-01 03:06:11 -0800
committerLinus Torvalds <torvalds@g5.osdl.org>2006-02-01 08:53:21 -0800
commit975b3d3d5b983eb60706d35f0d24cd19f6badabf (patch)
tree39d55db9236ef1acef4e955617296217c3a9fc02 /arch
parent4940fb441275d654cff7d0f7708f91bd8435a85a (diff)
[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: Mark Lord <mlord@pobox.com> Signed-off-by: Jens Axboe <axboe@suse.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'arch')
-rw-r--r--arch/i386/Kconfig37
1 files changed, 37 insertions, 0 deletions
diff --git a/arch/i386/Kconfig b/arch/i386/Kconfig
index 4e9e49a55ea..d86c865a7cd 100644
--- a/arch/i386/Kconfig
+++ b/arch/i386/Kconfig
@@ -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