PAE is useful for more than supporting more than 4GB RAM. It supports
expanded swapspace and NX executable protections. Some users may want
NX or expanded swapspace support without the overhead or instability
of highmem. For these reasons, the following patch divorces
CONFIG_X86_PAE from CONFIG_HIGHMEM64G.
vs. 2.6.22-rc4-mm2
Cc: Mark Lord <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Andrew Morton <[email protected]>
Signed-off-by: William Irwin <[email protected]>
Index: mm-2.6.22-rc4-2/arch/i386/Kconfig
===================================================================
--- mm-2.6.22-rc4-2.orig/arch/i386/Kconfig 2007-06-07 00:05:53.609599701 -0700
+++ mm-2.6.22-rc4-2/arch/i386/Kconfig 2007-06-07 17:02:24.333262965 -0700
@@ -544,6 +544,7 @@
config HIGHMEM64G
bool "64GB"
depends on X86_CMPXCHG64
+ select X86_PAE
help
Select this if you have a 32-bit processor and more than 4
gigabytes of physical RAM.
@@ -573,12 +574,12 @@
config VMSPLIT_3G
bool "3G/1G user/kernel split"
config VMSPLIT_3G_OPT
- depends on !HIGHMEM
+ depends on !X86_PAE
bool "3G/1G user/kernel split (for full 1G low memory)"
config VMSPLIT_2G
bool "2G/2G user/kernel split"
config VMSPLIT_2G_OPT
- depends on !HIGHMEM
+ depends on !X86_PAE
bool "2G/2G user/kernel split (for full 2G low memory)"
config VMSPLIT_1G
bool "1G/3G user/kernel split"
@@ -598,10 +599,15 @@
default y
config X86_PAE
- bool
- depends on HIGHMEM64G
- default y
+ bool "PAE (Physical Address Extension) Support"
+ default n
+ depends on !HIGHMEM4G
select RESOURCES_64BIT
+ help
+ PAE is required for NX support, and furthermore enables
+ larger swapspace support for non-overcommit purposes. It
+ has the cost of more pagetable lookup overhead, and also
+ consumes more pagetable space per process.
# Common NUMA Features
config NUMA
Index: mm-2.6.22-rc4-2/arch/i386/kernel/setup.c
===================================================================
--- mm-2.6.22-rc4-2.orig/arch/i386/kernel/setup.c 2007-06-06 23:52:18.839168580 -0700
+++ mm-2.6.22-rc4-2/arch/i386/kernel/setup.c 2007-06-07 17:02:24.349263876 -0700
@@ -273,18 +273,18 @@
printk(KERN_WARNING "Warning only %ldMB will be used.\n",
MAXMEM>>20);
if (max_pfn > MAX_NONPAE_PFN)
- printk(KERN_WARNING "Use a PAE enabled kernel.\n");
+ printk(KERN_WARNING "Use a HIGHMEM64G enabled kernel.\n");
else
printk(KERN_WARNING "Use a HIGHMEM enabled kernel.\n");
max_pfn = MAXMEM_PFN;
#else /* !CONFIG_HIGHMEM */
-#ifndef CONFIG_X86_PAE
+#ifndef CONFIG_HIGHMEM64G
if (max_pfn > MAX_NONPAE_PFN) {
max_pfn = MAX_NONPAE_PFN;
printk(KERN_WARNING "Warning only 4GB will be used.\n");
- printk(KERN_WARNING "Use a PAE enabled kernel.\n");
+ printk(KERN_WARNING "Use a HIGHMEM64G enabled kernel.\n");
}
-#endif /* !CONFIG_X86_PAE */
+#endif /* !CONFIG_HIGHMEM64G */
#endif /* !CONFIG_HIGHMEM */
} else {
if (highmem_pages == -1)
-
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