[ARM] add CONFIG_HIGHMEM option

Here it is... HIGHMEM for the ARM architecture.  :-)

If you don't have enough ram for highmem pages to be allocated and still
want to test this, then the cmdline option "vmalloc=" can be used with
a value large enough to force the highmem threshold down.

Successfully tested on a Marvell DB-78x00-BP Development Board with
2 GB of RAM.

Signed-off-by: Nicolas Pitre <nico@marvell.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index dbfdf87f993f..2b28786b3879 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -915,6 +915,23 @@ config NODES_SHIFT
         default "2"
         depends on NEED_MULTIPLE_NODES
 
+config HIGHMEM
+        bool "High Memory Support (EXPERIMENTAL)"
+        depends on MMU && EXPERIMENTAL
+        help
+          The address space of ARM processors is only 4 Gigabytes large
+          and it has to accommodate user address space, kernel address
+          space as well as some memory mapped IO. That means that, if you
+          have a large amount of physical memory and/or IO, not all of the
+          memory can be "permanently mapped" by the kernel. The physical
+          memory that is not permanently mapped is called "high memory".
+
+          Depending on the selected kernel/user memory split, minimum
+          vmalloc space and actual amount of RAM, you may not need this
+          option which should result in a slightly faster kernel.
+
+          If unsure, say n.
+
 source "mm/Kconfig"
 
 config LEDS