[PATCH] uml: allow finer tuning for host VMSPLIT setting

Now that various memory splits are enabled, add a config option allowing the
user to compile UML for its need - HOST_2G_2G allowed to choose either 3G/1G
or 2G/2G, and enabling it reduced the usable virtual memory.

Detecting this at run time should be implemented in the future, but we must
make the stop-gap measure work well enough (this is valid in _many_ cases).

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Cc: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/arch/um/Kconfig.i386 b/arch/um/Kconfig.i386
index f6eb72d..f191a55 100644 (file)
--- a/arch/um/Kconfig.i386
+++ b/arch/um/Kconfig.i386
@@ -16,23 +16,42 @@ config SEMAPHORE_SLEEPERS
        bool
        default y
 
-config HOST_2G_2G
-       bool "2G/2G host address space split"
-       default n
-       help
-       This is needed when the host on which you run has a 2G/2G memory
-       split, instead of the customary 3G/1G.
-
-       Note that to enable such a host
-       configuration, which makes sense only in some cases, you need special
-       host patches.
-
-       So, if you do not know what to do here, say 'N'.
+choice
+       prompt "Host memory split"
+       default HOST_VMSPLIT_3G
+       ---help---
+          This is needed when the host kernel on which you run has a non-default
+          (like 2G/2G) memory split, instead of the customary 3G/1G. If you did
+          not recompile your own kernel but use the default distro's one, you can
+          safely accept the "Default split" option.
+
+          It can be enabled on recent (>=2.6.16-rc2) vanilla kernels via
+          CONFIG_VM_SPLIT_*, or on previous kernels with special patches (-ck
+          patchset by Con Kolivas, or other ones) - option names match closely the
+          host CONFIG_VM_SPLIT_* ones.
+
+          A lower setting (where 1G/3G is lowest and 3G/1G is higher) will
+          tolerate even more "normal" host kernels, but an higher setting will be
+          stricter.
+
+          So, if you do not know what to do here, say 'Default split'.
+
+       config HOST_VMSPLIT_3G
+               bool "Default split (3G/1G user/kernel host split)"
+       config HOST_VMSPLIT_3G_OPT
+               bool "3G/1G user/kernel host split (for full 1G low memory)"
+       config HOST_VMSPLIT_2G
+               bool "2G/2G user/kernel host split"
+       config HOST_VMSPLIT_1G
+               bool "1G/3G user/kernel host split"
+endchoice
 
 config TOP_ADDR
-       hex
-       default 0xc0000000 if !HOST_2G_2G
-       default 0x80000000 if HOST_2G_2G
+       hex
+       default 0xB0000000 if HOST_VMSPLIT_3G_OPT
+       default 0x78000000 if HOST_VMSPLIT_2G
+       default 0x40000000 if HOST_VMSPLIT_1G
+       default 0xC0000000
 
 config 3_LEVEL_PGTABLES
        bool "Three-level pagetables (EXPERIMENTAL)"