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SubjectRe: [PATCH] 1-2-3 GB
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On Sat, Jan 12, 2002 at 07:22:23PM +0000, Hugh Dickins wrote:
> This patch is not actually what we've used. Paranoia (what other
> such bugs might there be?) drove me to set physical pages 0x3ffff
> and 0x40000 as Reserved in arch/i386/setup.c. I don't think it's
> appropriate to force that level of paranoia on others; but anyone
> configuring 3GBK should remember that it's a less-travelled path.
> Hugh

Thanks for the patch! I'm running on it on a 1024MB machine with
the 2GB option, and it passes LTP runalltests.sh.

The 3 patches in this thread combined into one, with a default
config option of 2GB, and help saying, if unsure, say "1GB":


diff -nur linux-2.4.18pre2aa2/Documentation/Configure.help
linux/Documentation/Configure.help
--- linux-2.4.18pre2aa2/Documentation/Configure.help Tue Jan 15 00:01:38
2002
+++ linux/Documentation/Configure.help Mon Jan 14 23:59:35 2002
@@ -376,6 +376,59 @@
Select this if you have a 32-bit processor and more than 4
gigabytes of physical RAM.

+# Choice: maxvm
+Maximum Virtual Memory
+CONFIG_1GB
+ If you have 4 Gigabytes of physical memory or less, you can change
+ where the where the kernel maps high memory. If you have less
+ than 1 gigabyte of physical memory, you should disable
+ CONFIG_HIGHMEM4G because you don't need the choices below.
+
+ If you have a large amount of physical memory, all of it may not
+ be "permanently mapped" by the kernel. The physical memory that
+ is not permanently mapped is called "high memory".
+
+ The numbers in the configuration options are not precise because
+ of the kernel's vmalloc() area, and the PCI space on motherboards
+ may vary as well. Typically there will 128 megabytes less
+ "user memory" mapped than the number in the configuration option.
+ Saying that another way, "high memory" will usually start 128
+ megabytes lower than the configuration option.
+
+ Selecting "05GB" results in a "3.5GB/0.5GB" kernel/user split:
+ 3.5 gigabytes are kernel mapped so each process sees a 3.5
+ gigabyte virtual memory space and the remaining part of the 4
+ gigabyte virtual memory space is used by the kernel to permanently
+ map as much physical memory as possible. On a system with 1 gigabyte
+ of physical memory, you may get 384 megabytes of "user memory" and
+ 640 megabytes of "high memory" with this selection.
+
+ Selecting "1GB" results in a "3GB/1GB" kernel/user split:
+ 3 gigabytes are mapped so each process sees a 3 gigabyte virtual
+ memory space and the remaining part of the 4 gigabyte virtual memory
+ space is used by the kernel to permanently map as much physical
+ memory as possible. On a system with 1 gigabyte of memory, you may
+ get 896 MB of "user memory" and 128 megabytes of "high memory"
+
+ Selecting "2GB" results in a "2GB/2GB" kernel/user split:
+ 2 gigabytes are mapped so each process sees a 2 gigabyte virtual
+ memory space and the remaining part of the 4 gigabyte virtual memory
+ space is used by the kernel to permanently map as much physical
+ memory as possible. On a system with 1 to 1.75 gigabytes of
+ physical memory, this option have all make it so no memory is
+ mapped as "high memory".
+
+ Selecting "3GB" results in a "1GB/3GB" kernel/user split:
+ 1 gigabyte is mapped so each process sees a 1 gigabyte virtual
+ memory space and the remaining part of the 4 gigabytes of virtual
+ memory space is used by the kernel to permanently map as much
+ physical memory as possible.
+
+ Options "2GB" and "3GB" may expose bugs that were dormant in
+ certain hardware, compilers, and possibly even the kernel.
+
+ If unsure, say "1GB".
+
HIGHMEM I/O support
CONFIG_HIGHIO
If you want to be able to do I/O to high memory pages, say Y.
diff -nur linux-2.4.18pre2aa2/Rules.make linux/Rules.make
--- linux-2.4.18pre2aa2/Rules.make Tue Mar 6 22:31:01 2001
+++ linux/Rules.make Mon Jan 14 23:58:55 2002
@@ -212,6 +212,7 @@
#
# 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
@@ -220,6 +221,22 @@
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
@if [ ! -r $(MODINCL)/$*.stamp -o $(MODINCL)/$*.stamp -ot $< ]; then
\
echo '$(CC) $(CFLAGS) $(EXTRA_CFLAGS) -E -D__GENKSYMS__ $<';
\
diff -nur linux-2.4.18pre2aa2/arch/i386/config.in linux/arch/i386/config.in
--- linux-2.4.18pre2aa2/arch/i386/config.in Tue Jan 15 00:01:38 2002
+++ linux/arch/i386/config.in Mon Jan 14 23:58:55 2002
@@ -169,7 +169,11 @@
if [ "$CONFIG_HIGHMEM64G" = "y" ]; then
define_bool CONFIG_X86_PAE y
else
- bool '3.5GB user address space' CONFIG_05GB
+ choice 'Maximum Virtual Memory' \
+ "3GB CONFIG_1GB \
+ 2GB CONFIG_2GB \
+ 1GB CONFIG_3GB \
+ 05GB CONFIG_05GB" 2GB
fi
if [ "$CONFIG_NOHIGHMEM" = "y" ]; then
define_bool CONFIG_NO_PAGE_VIRTUAL y
@@ -179,6 +183,7 @@
bool 'HIGHMEM I/O support (EXPERIMENTAL)' CONFIG_HIGHIO
fi

+
bool 'Math emulation' CONFIG_MATH_EMULATION
bool 'MTRR (Memory Type Range Register) support' CONFIG_MTRR
bool 'Symmetric multi-processing support' CONFIG_SMP
diff -nur linux-2.4.18pre2aa2/include/asm-i386/page_offset.h
linux/include/asm-i386/page_offset.h
--- linux-2.4.18pre2aa2/include/asm-i386/page_offset.h Tue Jan 15 00:01:38
2002
+++ linux/include/asm-i386/page_offset.h Mon Jan 14 23:58:55 2002
@@ -1,6 +1,10 @@
#include <linux/config.h>
-#ifndef CONFIG_05GB
-#define PAGE_OFFSET_RAW 0xC0000000
-#else
+#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 -nur linux-2.4.18pre2aa2/mm/memory.c linux/mm/memory.c
--- linux-2.4.18pre2aa2/mm/memory.c Tue Jan 15 00:01:38 2002
+++ linux/mm/memory.c Mon Jan 14 23:59:18 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);
}
--
Randy Hron
-
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