parisc,metag: Do not hardcode maximum userspace stack size

This patch affects only architectures where the stack grows upwards
(currently parisc and metag only). On those do not hardcode the maximum
initial stack size to 1GB for 32-bit processes, but make it configurable
via a config option.

The main problem with the hardcoded stack size is, that we have two
memory regions which grow upwards: stack and heap. To keep most of the
memory available for heap in a flexmap memory layout, it makes no sense
to hard allocate up to 1GB of the memory for stack which can't be used
as heap then.

This patch makes the stack size for 32-bit processes configurable and
uses 80MB as default value which has been in use during the last few
years on parisc and which hasn't showed any problems yet.

Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: "James E.J. Bottomley" <jejb@parisc-linux.org>
Cc: linux-parisc@vger.kernel.org
Cc: linux-metag@vger.kernel.org
Cc: John David Anglin <dave.anglin@bell.net>

1 files changed, 15 insertions, 0 deletions

diff --git a/mm/Kconfig b/mm/Kconfig
index ebe5880c29d6..1b5a95f0fa01 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -581,3 +581,18 @@ config PGTABLE_MAPPING
 
 config GENERIC_EARLY_IOREMAP
         bool
+
+config MAX_STACK_SIZE_MB
+        int "Maximum user stack size for 32-bit processes (MB)"
+        default 80
+        range 8 256 if METAG
+        range 8 2048
+        depends on STACK_GROWSUP && (!64BIT || COMPAT)
+        help
+          This is the maximum stack size in Megabytes in the VM layout of 32-bit
+          user processes when the stack grows upwards (currently only on parisc
+          and metag arch). The stack will be located at the highest memory
+          address minus the given value, unless the RLIMIT_STACK hard limit is
+          changed to a smaller value in which case that is used.
+
+          A sane initial value is 80 MB.