Thanks! Updated patch below.

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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 <axb...@suse.de> Acked-by: Ingo Molnar <min...@elte.hu>

diff --git a/arch/i386/Kconfig b/arch/i386/Kconfig index d849c68..20d1423 100644 --- a/arch/i386/Kconfig +++ b/arch/i386/Kconfig @@ -444,6 +464,35 @@ 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 increasing the kernel address space limits the range + available to user programs, making the address space there + tighter. + + If you are not absolutely sure what you are doing, leave this + option alone! + + 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/arch/i386/mm/init.c b/arch/i386/mm/init.c index 7df494b..67f1da0 100644 --- a/arch/i386/mm/init.c +++ b/arch/i386/mm/init.c @@ -597,6 +597,12 @@ void __init mem_init(void) high_memory = (void *) __va(max_low_pfn * PAGE_SIZE - 1) + 1; #endif

+#if !defined(CONFIG_DEFAULT_3G) + /* if the user has less than 960MB of RAM, he should use the default */ + if (max_low_pfn < (960 * 1024 * 1024 / PAGE_SIZE)) + printk(KERN_INFO "Memory: less than 960MiB of RAM, you should use the default
memory split setting\n"); +#endif + /* this will put all low memory onto the freelists */ totalram_pages += free_all_bootmem();

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)