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SubjectRe: x86 question: Can a process have > 3GB memory?
From
Date
On Tue, 2002-05-07 at 16:03, Clifford White wrote:

> We are working with a database that requires a large amount of memory
> allocated by a single process.
> This is on an Intel 32-bit platform.
> We'd like to go > 3GB of memory per process.
> Is this possible on a 32-bit machine? I have been reading the various
> 'highmem' discussions, but that's kernel page tables...
> Or is this a glibc issue, and not proper for a kernel-list question?
> Any pointers would be appreciated. The Intel ESMA (Extended Server Memory
> Arch) page states that it's possible, but.....how?

You can go to 3.5GB, anything more and stuff starts getting real tight
and not very nice. You can only do 3.5/0.5 on non-PAE, though - PAE
requires segments to be aligned on 1GB-boundaries.

The attached patch (for which credit goes elsewhere - Ingo or Randy, I
think?) implements the full range of 1 to 3.5GB user space partitioning,
selectable at compile-time.

Robert Love

diff -urN 2.4.18pre7/Rules.make 3g/Rules.make
--- 2.4.18pre7/Rules.make Thu Jan 24 02:05:25 2002
+++ 3g/Rules.make Mon Jan 28 05:55:28 2002
@@ -214,12 +214,29 @@
#
# 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

$(MODINCL)/%.ver: %.c
diff -urN 2.4.18pre7/arch/i386/Makefile 3g/arch/i386/Makefile
--- 2.4.18pre7/arch/i386/Makefile Tue May 1 19:35:18 2001
+++ 3g/arch/i386/Makefile Mon Jan 28 05:55:28 2002
@@ -106,6 +106,9 @@

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

FORCE: ;
@@ -142,6 +145,7 @@
@$(MAKEBOOT) clean

archmrproper:
+ rm -f arch/i386/vmlinux.lds

archdep:
@$(MAKEBOOT) dep
diff -urN 2.4.18pre7/arch/i386/config.in 3g/arch/i386/config.in
--- 2.4.18pre7/arch/i386/config.in Thu Jan 24 02:05:26 2002
+++ 3g/arch/i386/config.in Mon Jan 28 05:55:30 2002
@@ -171,12 +171,23 @@
"off CONFIG_NOHIGHMEM \
4GB CONFIG_HIGHMEM4G \
64GB CONFIG_HIGHMEM64G" off
-if [ "$CONFIG_HIGHMEM4G" = "y" ]; then
+if [ "$CONFIG_HIGHMEM4G" = "y" -o "$CONFIG_HIGHMEM64G" = "y" ]; then
define_bool CONFIG_HIGHMEM y
+else
+ define_bool CONFIG_HIGHMEM n
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
diff -urN 2.4.18pre7/arch/i386/vmlinux.lds 3g/arch/i386/vmlinux.lds
--- 2.4.18pre7/arch/i386/vmlinux.lds Thu Jan 24 02:05:26 2002
+++ 3g/arch/i386/vmlinux.lds Thu Jan 1 01:00:00 1970
@@ -1,82 +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)
-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 : { *(.initcall.init) }
- __initcall_end = .;
- . = ALIGN(4096);
- __init_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 -urN 2.4.18pre7/arch/i386/vmlinux.lds.S 3g/arch/i386/vmlinux.lds.S
--- 2.4.18pre7/arch/i386/vmlinux.lds.S Thu Jan 1 01:00:00 1970
+++ 3g/arch/i386/vmlinux.lds.S Mon Jan 28 05:55:28 2002
@@ -0,0 +1,82 @@
+/* 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)
+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 : { *(.initcall.init) }
+ __initcall_end = .;
+ . = ALIGN(4096);
+ __init_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 -urN 2.4.18pre7/include/asm-i386/page.h 3g/include/asm-i386/page.h
--- 2.4.18pre7/include/asm-i386/page.h Thu Jan 24 02:06:02 2002
+++ 3g/include/asm-i386/page.h Mon Jan 28 05:55:28 2002
@@ -78,7 +78,9 @@
* 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 -urN 2.4.18pre7/include/asm-i386/page_offset.h 3g/include/asm-i386/page_offset.h
--- 2.4.18pre7/include/asm-i386/page_offset.h Thu Jan 1 01:00:00 1970
+++ 3g/include/asm-i386/page_offset.h Mon Jan 28 05:55:28 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 -urN 2.4.18pre7/include/asm-i386/processor.h 3g/include/asm-i386/processor.h
--- 2.4.18pre7/include/asm-i386/processor.h Tue Jan 22 18:55:59 2002
+++ 3g/include/asm-i386/processor.h Mon Jan 28 05:55:28 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 -urN 2.4.18pre7/mm/memory.c 3g/mm/memory.c
--- 2.4.18pre7/mm/memory.c Tue Jan 22 18:56:30 2002
+++ 3g/mm/memory.c Mon Jan 28 05:55:28 2002
@@ -106,8 +106,7 @@

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

if (pgd_none(*dir))
return;
@@ -118,9 +117,23 @@
}
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(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(md);
}
pmd_free(pmd);
}
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