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Subject[PATCH] make PAGE_OFFSET config option on x86
Whether they're a user that is doing a scientific application that 
needs more than 3GB, or a large PAE machine that needs more
ZONE_NORMAL, lots of people are applying patches to change
PAGE_OFFSET. This patch lets you do it in a config option. It is a
port from Andrea's 2.4 tree, and I believe that Ingo is the original
author.

Andrea's patch didn't have a Config.help entry for this option, so I
wrote one. I may not have all of the necessary context to explain it,
so any comments there would be appreciated.
--
Dave Hansen
haveblue@us.ibm.com
# This is a BitKeeper generated patch for the following project:
# Project Name: Linux kernel tree
# This patch format is intended for GNU patch command version 2.5 or higher.
# This patch includes the following deltas:
# ChangeSet 1.489 -> 1.491
# include/asm-i386/processor.h 1.28 -> 1.29
# arch/i386/Config.help 1.12 -> 1.13
# include/asm-i386/page.h 1.15 -> 1.16
# arch/i386/vmlinux.lds 1.9 -> (deleted)
# arch/i386/config.in 1.46 -> 1.47
# arch/i386/Makefile 1.16 -> 1.17
# Rules.make 1.68 -> 1.69
# mm/memory.c 1.83 -> 1.85
# (new) -> 1.1 arch/i386/vmlinux.lds.S
# (new) -> 1.1 include/asm-i386/page_offset.h
#
# The following is the BitKeeper ChangeSet Log
# --------------------------------------------
# 02/08/19 haveblue@elm3b96.(none) 1.490
# merge Andrea's PAGE_OFFSET configuration option
# --------------------------------------------
# 02/08/19 haveblue@elm3b96.(none) 1.491
# fix merge bug
#
# add Config.help entry
# --------------------------------------------
#
diff -Nru a/Rules.make b/Rules.make
--- a/Rules.make Mon Aug 19 13:28:19 2002
+++ b/Rules.make Mon Aug 19 13:28:19 2002
@@ -149,12 +149,29 @@
#
# Added the SMP separator to stop module accidents between uniprocessor
# and SMP Intel boxes - AC - from bits by Michael Chastain
+# Added separator for different PAGE_OFFSET memory models - Ingo.
#

ifdef CONFIG_SMP
genksyms_smp_prefix := -p smp_
else
genksyms_smp_prefix :=
+endif
+
+ifdef CONFIG_2GB
+ifdef CONFIG_SMP
+ genksyms_smp_prefix := -p smp_2gig_
+else
+ genksyms_smp_prefix := -p 2gig_
+endif
+endif
+
+ifdef CONFIG_3GB
+ifdef CONFIG_SMP
+ genksyms_smp_prefix := -p smp_3gig_
+else
+ genksyms_smp_prefix := -p 3gig_
+endif
endif

# Don't include modversions.h, we're just about to generate it here.
diff -Nru a/arch/i386/Config.help b/arch/i386/Config.help
--- a/arch/i386/Config.help Mon Aug 19 13:28:19 2002
+++ b/arch/i386/Config.help Mon Aug 19 13:28:19 2002
@@ -128,6 +128,27 @@

If unsure, say "off".

+CONFIG_1GB
+ On i386, a process can only virtually address 4GB of memory. This
+ lets you select how much of that virtual space you would like to
+ devoted to userspace, and how much to the kernel.
+
+ Some userspace programs would like to address as much as possible and
+ have few demands of the kernel other than it get out of the way. These
+ users may opt to use the 3.5GB option to give their userspace program
+ as much room as possible. Due to alignment issues imposed by PAE,
+ the "3.5GB" option is unavailable if "64GB" high memory support is
+ enabled.
+
+ Other users (especially those who use PAE) may be running out of
+ ZONE_NORMAL memory. Those users may benefit from increasing the
+ kernel's virtual address space size by taking it away from userspace,
+ which may not need all of its space. An indicator that this is
+ happening is when /proc/Meminfo's "LowFree:" is a small percentage of
+ "LowTotal:" while "HighFree:" is very large.
+
+ If unsure, say "3GB"
+
CONFIG_HIGHPTE
The VM uses one page table entry for each page of physical memory.
For systems with a lot of RAM, this can be wasteful of precious
diff -Nru a/arch/i386/Makefile b/arch/i386/Makefile
--- a/arch/i386/Makefile Mon Aug 19 13:28:19 2002
+++ b/arch/i386/Makefile Mon Aug 19 13:28:19 2002
@@ -104,6 +104,9 @@

MAKEBOOT = +$(MAKE) -C arch/$(ARCH)/boot

+arch/i386/vmlinux.lds: arch/i386/vmlinux.lds.S FORCE
+ $(CPP) -C -P -I$(HPATH) -imacros $(HPATH)/asm-i386/page_offset.h -Ui386 arch/i386/vmlinux.lds.S >arch/i386/vmlinux.lds
+
vmlinux: arch/i386/vmlinux.lds

.PHONY: zImage bzImage compressed zlilo bzlilo zdisk bzdisk install \
@@ -141,3 +144,4 @@
@$(MAKEBOOT) clean

archmrproper:
+ rm -f arch/i386/vmlinux.lds
diff -Nru a/arch/i386/config.in b/arch/i386/config.in
--- a/arch/i386/config.in Mon Aug 19 13:28:19 2002
+++ b/arch/i386/config.in Mon Aug 19 13:28:19 2002
@@ -186,14 +186,24 @@
4GB CONFIG_HIGHMEM4G \
64GB CONFIG_HIGHMEM64G" off

-if [ "$CONFIG_HIGHMEM4G" = "y" ]; then
+if [ "$CONFIG_HIGHMEM4G" = "y" -o "$CONFIG_HIGHMEM64G" = "y" ]; then
define_bool CONFIG_HIGHMEM y
fi

if [ "$CONFIG_HIGHMEM64G" = "y" ]; then
- define_bool CONFIG_HIGHMEM y
define_bool CONFIG_X86_PAE y
+ choice 'User address space size' \
+ "3GB CONFIG_1GB \
+ 2GB CONFIG_2GB \
+ 1GB CONFIG_3GB" 3GB
+else
+ choice 'User address space size' \
+ "3GB CONFIG_1GB \
+ 2GB CONFIG_2GB \
+ 1GB CONFIG_3GB \
+ 3.5GB CONFIG_05GB" 3GB
fi
+

bool 'Math emulation' CONFIG_MATH_EMULATION
bool 'MTRR (Memory Type Range Register) support' CONFIG_MTRR
diff -Nru a/arch/i386/vmlinux.lds b/arch/i386/vmlinux.lds
--- a/arch/i386/vmlinux.lds Mon Aug 19 13:28:19 2002
+++ /dev/null Wed Dec 31 16:00:00 1969
@@ -1,101 +0,0 @@
-/* ld script to make i386 Linux kernel
- * Written by Martin Mares <mj@atrey.karlin.mff.cuni.cz>;
- */
-OUTPUT_FORMAT("elf32-i386", "elf32-i386", "elf32-i386")
-OUTPUT_ARCH(i386)
-ENTRY(_start)
-jiffies = jiffies_64;
-SECTIONS
-{
- . = 0xC0000000 + 0x100000;
- _text = .; /* Text and read-only data */
- .text : {
- *(.text)
- *(.fixup)
- *(.gnu.warning)
- } = 0x9090
-
- _etext = .; /* End of text section */
-
- .rodata : { *(.rodata) *(.rodata.*) }
- .kstrtab : { *(.kstrtab) }
-
- . = ALIGN(16); /* Exception table */
- __start___ex_table = .;
- __ex_table : { *(__ex_table) }
- __stop___ex_table = .;
-
- __start___ksymtab = .; /* Kernel symbol table */
- __ksymtab : { *(__ksymtab) }
- __stop___ksymtab = .;
-
- .data : { /* Data */
- *(.data)
- CONSTRUCTORS
- }
-
- _edata = .; /* End of data section */
-
- . = ALIGN(8192); /* init_task */
- .data.init_task : { *(.data.init_task) }
-
- . = ALIGN(4096); /* Init code and data */
- __init_begin = .;
- .text.init : { *(.text.init) }
- .data.init : { *(.data.init) }
- . = ALIGN(16);
- __setup_start = .;
- .setup.init : { *(.setup.init) }
- __setup_end = .;
- __initcall_start = .;
- .initcall.init : {
- *(.initcall1.init)
- *(.initcall2.init)
- *(.initcall3.init)
- *(.initcall4.init)
- *(.initcall5.init)
- *(.initcall6.init)
- *(.initcall7.init)
- }
- __initcall_end = .;
- . = ALIGN(32);
- __per_cpu_start = .;
- .data.percpu : { *(.data.percpu) }
- __per_cpu_end = .;
- . = ALIGN(4096);
- __init_end = .;
-
- . = ALIGN(4096);
- __nosave_begin = .;
- .data_nosave : { *(.data.nosave) }
- . = ALIGN(4096);
- __nosave_end = .;
-
- . = ALIGN(4096);
- .data.page_aligned : { *(.data.idt) }
-
- . = ALIGN(32);
- .data.cacheline_aligned : { *(.data.cacheline_aligned) }
-
- __bss_start = .; /* BSS */
- .bss : {
- *(.bss)
- }
- _end = . ;
-
- /* Sections to be discarded */
- /DISCARD/ : {
- *(.text.exit)
- *(.data.exit)
- *(.exitcall.exit)
- }
-
- /* Stabs debugging sections. */
- .stab 0 : { *(.stab) }
- .stabstr 0 : { *(.stabstr) }
- .stab.excl 0 : { *(.stab.excl) }
- .stab.exclstr 0 : { *(.stab.exclstr) }
- .stab.index 0 : { *(.stab.index) }
- .stab.indexstr 0 : { *(.stab.indexstr) }
- .comment 0 : { *(.comment) }
-}
diff -Nru a/arch/i386/vmlinux.lds.S b/arch/i386/vmlinux.lds.S
--- /dev/null Wed Dec 31 16:00:00 1969
+++ b/arch/i386/vmlinux.lds.S Mon Aug 19 13:28:19 2002
@@ -0,0 +1,101 @@
+/* ld script to make i386 Linux kernel
+ * Written by Martin Mares <mj@atrey.karlin.mff.cuni.cz>;
+ */
+OUTPUT_FORMAT("elf32-i386", "elf32-i386", "elf32-i386")
+OUTPUT_ARCH(i386)
+ENTRY(_start)
+jiffies = jiffies_64;
+SECTIONS
+{
+ . = PAGE_OFFSET_RAW + 0x100000;
+ _text = .; /* Text and read-only data */
+ .text : {
+ *(.text)
+ *(.fixup)
+ *(.gnu.warning)
+ } = 0x9090
+
+ _etext = .; /* End of text section */
+
+ .rodata : { *(.rodata) *(.rodata.*) }
+ .kstrtab : { *(.kstrtab) }
+
+ . = ALIGN(16); /* Exception table */
+ __start___ex_table = .;
+ __ex_table : { *(__ex_table) }
+ __stop___ex_table = .;
+
+ __start___ksymtab = .; /* Kernel symbol table */
+ __ksymtab : { *(__ksymtab) }
+ __stop___ksymtab = .;
+
+ .data : { /* Data */
+ *(.data)
+ CONSTRUCTORS
+ }
+
+ _edata = .; /* End of data section */
+
+ . = ALIGN(8192); /* init_task */
+ .data.init_task : { *(.data.init_task) }
+
+ . = ALIGN(4096); /* Init code and data */
+ __init_begin = .;
+ .text.init : { *(.text.init) }
+ .data.init : { *(.data.init) }
+ . = ALIGN(16);
+ __setup_start = .;
+ .setup.init : { *(.setup.init) }
+ __setup_end = .;
+ __initcall_start = .;
+ .initcall.init : {
+ *(.initcall1.init)
+ *(.initcall2.init)
+ *(.initcall3.init)
+ *(.initcall4.init)
+ *(.initcall5.init)
+ *(.initcall6.init)
+ *(.initcall7.init)
+ }
+ __initcall_end = .;
+ . = ALIGN(32);
+ __per_cpu_start = .;
+ .data.percpu : { *(.data.percpu) }
+ __per_cpu_end = .;
+ . = ALIGN(4096);
+ __init_end = .;
+
+ . = ALIGN(4096);
+ __nosave_begin = .;
+ .data_nosave : { *(.data.nosave) }
+ . = ALIGN(4096);
+ __nosave_end = .;
+
+ . = ALIGN(4096);
+ .data.page_aligned : { *(.data.idt) }
+
+ . = ALIGN(32);
+ .data.cacheline_aligned : { *(.data.cacheline_aligned) }
+
+ __bss_start = .; /* BSS */
+ .bss : {
+ *(.bss)
+ }
+ _end = . ;
+
+ /* Sections to be discarded */
+ /DISCARD/ : {
+ *(.text.exit)
+ *(.data.exit)
+ *(.exitcall.exit)
+ }
+
+ /* Stabs debugging sections. */
+ .stab 0 : { *(.stab) }
+ .stabstr 0 : { *(.stabstr) }
+ .stab.excl 0 : { *(.stab.excl) }
+ .stab.exclstr 0 : { *(.stab.exclstr) }
+ .stab.index 0 : { *(.stab.index) }
+ .stab.indexstr 0 : { *(.stab.indexstr) }
+ .comment 0 : { *(.comment) }
+}
diff -Nru a/include/asm-i386/page.h b/include/asm-i386/page.h
--- a/include/asm-i386/page.h Mon Aug 19 13:28:19 2002
+++ b/include/asm-i386/page.h Mon Aug 19 13:28:19 2002
@@ -81,7 +81,9 @@
* and CONFIG_HIGHMEM64G options in the kernel configuration.
*/

-#define __PAGE_OFFSET (0xC0000000)
+#include <asm/page_offset.h>
+
+#define __PAGE_OFFSET (PAGE_OFFSET_RAW)

/*
* This much address space is reserved for vmalloc() and iomap()
diff -Nru a/include/asm-i386/page_offset.h b/include/asm-i386/page_offset.h
--- /dev/null Wed Dec 31 16:00:00 1969
+++ b/include/asm-i386/page_offset.h Mon Aug 19 13:28:19 2002
@@ -0,0 +1,10 @@
+#include <linux/config.h>
+#ifdef CONFIG_05GB
+#define PAGE_OFFSET_RAW 0xE0000000
+#elif defined(CONFIG_1GB)
+#define PAGE_OFFSET_RAW 0xC0000000
+#elif defined(CONFIG_2GB)
+#define PAGE_OFFSET_RAW 0x80000000
+#elif defined(CONFIG_3GB)
+#define PAGE_OFFSET_RAW 0x40000000
+#endif
diff -Nru a/include/asm-i386/processor.h b/include/asm-i386/processor.h
--- a/include/asm-i386/processor.h Mon Aug 19 13:28:19 2002
+++ b/include/asm-i386/processor.h Mon Aug 19 13:28:19 2002
@@ -270,7 +270,11 @@
/* This decides where the kernel will search for a free chunk of vm
* space during mmap's.
*/
+#ifndef CONFIG_05GB
#define TASK_UNMAPPED_BASE (TASK_SIZE / 3)
+#else
+#define TASK_UNMAPPED_BASE (TASK_SIZE / 16)
+#endif

/*
* Size of io_bitmap in longwords: 32 is ports 0-0x3ff.
diff -Nru a/mm/memory.c b/mm/memory.c
--- a/mm/memory.c Mon Aug 19 13:28:19 2002
+++ b/mm/memory.c Mon Aug 19 13:28:19 2002
@@ -97,8 +97,7 @@

static inline void free_one_pgd(mmu_gather_t *tlb, pgd_t * dir)
{
- int j;
- pmd_t * pmd;
+ pmd_t * pmd, * md, * emd;

if (pgd_none(*dir))
return;
@@ -109,9 +108,23 @@
}
pmd = pmd_offset(dir, 0);
pgd_clear(dir);
- for (j = 0; j < PTRS_PER_PMD ; j++) {
- prefetchw(pmd+j+(PREFETCH_STRIDE/16));
- free_one_pmd(tlb, pmd+j);
+
+ /*
+ * Beware if changing the loop below. It once used int j,
+ * for (j = 0; j < PTRS_PER_PMD; j++)
+ * free_one_pmd(pmd+j);
+ * but some older i386 compilers (e.g. egcs-2.91.66, gcc-2.95.3)
+ * terminated the loop with a _signed_ address comparison
+ * using "jle", when configured for HIGHMEM64GB (X86_PAE).
+ * If also configured for 3GB of kernel virtual address space,
+ * if page at physical 0x3ffff000 virtual 0x7ffff000 is used as
+ * a pmd, when that mm exits the loop goes on to free "entries"
+ * found at 0x80000000 onwards. The loop below compiles instead
+ * to be terminated by unsigned address comparison using "jb".
+ */
+ for (md = pmd, emd = pmd + PTRS_PER_PMD; md < emd; md++) {
+ prefetchw(md+(PREFETCH_STRIDE/16));
+ free_one_pmd(tlb,md);
}
pmd_free_tlb(tlb, pmd);
}
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