s390: remove small stack config option

We've seen repeatedly that 8KB stack size on 64 bit kernels
is not sufficient.
So simply remove the config option.
Signed-off-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/Kconfig

@@ -375,19 +375,6 @@ config PACK_STACK
 
 	  Say Y if you are unsure.
 
-config SMALL_STACK
-	def_bool n
-	prompt "Use 8kb for kernel stack instead of 16kb"
-	depends on PACK_STACK && 64BIT && !LOCKDEP
-	help
-	  If you say Y here and the compiler supports the -mkernel-backchain
-	  option the kernel will use a smaller kernel stack size. The reduced
-	  size is 8kb instead of 16kb. This allows to run more threads on a
-	  system and reduces the pressure on the memory management for higher
-	  order page allocations.
-
-	  Say N if you are unsure.
-
 config CHECK_STACK
 	def_bool y
 	prompt "Detect kernel stack overflow"

arch/s390/Makefile

@@ -55,22 +55,12 @@ cflags-$(CONFIG_FRAME_POINTER) += -fno-optimize-sibling-calls
 ifeq ($(call cc-option-yn,-mkernel-backchain),y)
 cflags-$(CONFIG_PACK_STACK)  += -mkernel-backchain -D__PACK_STACK
 aflags-$(CONFIG_PACK_STACK)  += -D__PACK_STACK
-cflags-$(CONFIG_SMALL_STACK) += -D__SMALL_STACK
-aflags-$(CONFIG_SMALL_STACK) += -D__SMALL_STACK
-ifdef CONFIG_SMALL_STACK
-STACK_SIZE := $(shell echo $$(($(STACK_SIZE)/2)) )
-endif
 endif
 
 # new style option for packed stacks
 ifeq ($(call cc-option-yn,-mpacked-stack),y)
 cflags-$(CONFIG_PACK_STACK)  += -mpacked-stack -D__PACK_STACK
 aflags-$(CONFIG_PACK_STACK)  += -D__PACK_STACK
-cflags-$(CONFIG_SMALL_STACK) += -D__SMALL_STACK
-aflags-$(CONFIG_SMALL_STACK) += -D__SMALL_STACK
-ifdef CONFIG_SMALL_STACK
-STACK_SIZE := $(shell echo $$(($(STACK_SIZE)/2)) )
-endif
 endif
 
 ifeq ($(call cc-option-yn,-mstack-size=8192 -mstack-guard=128),y)

arch/s390/include/asm/thread_info.h

@@ -14,13 +14,8 @@
 #define THREAD_ORDER 1
 #define ASYNC_ORDER  1
 #else /* CONFIG_64BIT */
-#ifndef __SMALL_STACK
 #define THREAD_ORDER 2
 #define ASYNC_ORDER  2
-#else
-#define THREAD_ORDER 1
-#define ASYNC_ORDER  1
-#endif
 #endif /* CONFIG_64BIT */
 
 #define THREAD_SIZE (PAGE_SIZE << THREAD_ORDER)