On Tue, Jan 10 2006, Byron Stanoszek wrote:
> On Tue, 10 Jan 2006, Jens Axboe wrote:
>
> >>yes, i made it totally configurable in 2.4 days: 1:3, 2/2 and 3:1 splits
> >>were possible. It was a larger patch to enable all this across x86, but
> >>the Kconfig portion was removed a bit later because people _frequently_
> >>misconfigured their kernels and then complained about the results.
> >
> >How is this different than all other sorts of misconfigurations? As far
> >as I can tell, the biggest "problem" for some is if they depend on some
> >binary module that will of course break with a different page offset.
> >
> >For simplicity, I didn't add more than the 2/2 split, where we could add
> >even a 3/1 kernel/user or a 0.5/3.5 (I think sles8 had this).
>
> I prefer setting __PAGE_OFFSET to (0x78000000) on machines with 2GB of RAM.
> This seems to let the kernel use the full 2GB of memory, rather than just
> 1920-1984 MB (at least back in 2.4 days).
A newer version, trying to cater to the various comments in here.
Changes:
- Add 1G_OPT split, meant for 1GiB machines. Uses 0xB0000000
- Add 1G/3G split
- Move the 2G/2G a little, so the full 2GiB of ram can be mapped.
- Improve help text (I hope :)
- Make option depend on EXPERIMENTAL.
- Make the page.h a lot more readable.
---
Add option for configuring the page offset, to better optimize the
kernel for higher memory machines. Enables users to get rid of high
memory for eg a 1GiB machine.
Signed-off-by: Jens Axboe <[email protected]>
diff --git a/arch/i386/Kconfig b/arch/i386/Kconfig
index d849c68..fcad8f7 100644
--- a/arch/i386/Kconfig
+++ b/arch/i386/Kconfig
@@ -444,6 +464,32 @@ config HIGHMEM64G
endchoice
+choice
+ depends on NOHIGHMEM && EXPERIMENTAL
+ prompt "Memory split"
+ default DEFAULT_3G
+ help
+ Select the wanted 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 selecting anything but the default 3G/1G split will make
+ your kernel incompatible with binary only modules.
+
+ config DEFAULT_3G
+ bool "3G/1G user/kernel split"
+ config DEFAULT_3G_OPT
+ bool "3G/1G user/kernel split (for full 1G low memory)"
+ config DEFAULT_2G
+ bool "2G/2G user/kernel split"
+ config DEFAULT_1G
+ bool "1G/3G user/kernel split"
+
+endchoice
+
config HIGHMEM
bool
depends on HIGHMEM64G || HIGHMEM4G
diff --git a/include/asm-i386/page.h b/include/asm-i386/page.h
index 73296d9..7da50a1 100644
--- a/include/asm-i386/page.h
+++ b/include/asm-i386/page.h
@@ -109,11 +109,23 @@ extern int page_is_ram(unsigned long pag
#endif /* __ASSEMBLY__ */
+#if defined(CONFIG_DEFAULT_3G)
+#define __PAGE_OFFSET_RAW (0xC0000000)
+#elif defined(CONFIG_DEFAULT_3G_OPT)
+#define __PAGE_OFFSET_RAW (0xB0000000)
+#elif defined(CONFIG_DEFAULT_2G)
+#define __PAGE_OFFSET_RAW (0x78000000)
+#elif defined(CONFIG_DEFAULT_1G)
+#define __PAGE_OFFSET_RAW (0x40000000)
+#else
+#error "Bad user/kernel offset"
+#endif
+
#ifdef __ASSEMBLY__
-#define __PAGE_OFFSET (0xC0000000)
+#define __PAGE_OFFSET __PAGE_OFFSET_RAW
#define __PHYSICAL_START CONFIG_PHYSICAL_START
#else
-#define __PAGE_OFFSET (0xC0000000UL)
+#define __PAGE_OFFSET ((unsigned long)__PAGE_OFFSET_RAW)
#define __PHYSICAL_START ((unsigned long)CONFIG_PHYSICAL_START)
#endif
#define __KERNEL_START (__PAGE_OFFSET + __PHYSICAL_START)
--
Jens Axboe
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