In preparation for reducing stack size, add a machanism to see how
much of a kernel stack is used. This fills a new stack with 0x6b on
allocation and sees where the lowest non-0x6b byte is on process
exit. It keeps track of the lowest value and logs values as they get
lower.
The lowest values I've seen so far are ~1250 bytes remaining on i386
(with order 0 stacks) and ~2650 on x86_64 (order 1).
Signed-off-by: Jeff Dike <[email protected]>
--
arch/um/Kconfig.debug | 8 ++++++++
arch/um/defconfig | 1 +
arch/um/kernel/process.c | 35 +++++++++++++++++++++++++++++++++++
include/asm-um/thread_info.h | 16 ++++++++++++++++
4 files changed, 60 insertions(+)
Index: linux-2.6.21-mm/arch/um/Kconfig.debug
===================================================================
--- linux-2.6.21-mm.orig/arch/um/Kconfig.debug 2007-05-09 14:34:39.000000000 -0400
+++ linux-2.6.21-mm/arch/um/Kconfig.debug 2007-05-09 14:36:10.000000000 -0400
@@ -47,4 +47,12 @@ config GCOV
If you're involved in UML kernel development and want to use gcov,
say Y. If you're unsure, say N.
+config STACK_USAGE
+ bool "Track kernel stack usage"
+ default N
+ help
+ Track the maximum kernel stack usage - this will look at each
+ kernel stack at process exit and log it if it's the deepest
+ stack seen so far.
+
endmenu
Index: linux-2.6.21-mm/arch/um/kernel/process.c
===================================================================
--- linux-2.6.21-mm.orig/arch/um/kernel/process.c 2007-05-09 14:34:39.000000000 -0400
+++ linux-2.6.21-mm/arch/um/kernel/process.c 2007-05-09 14:36:10.000000000 -0400
@@ -427,3 +427,38 @@ unsigned long arch_align_stack(unsigned
return sp & ~0xf;
}
#endif
+
+#ifdef CONFIG_STACK_USAGE
+
+static int lowest_to_date = THREAD_SIZE;
+
+void mark_stack(struct thread_info *stack)
+{
+ if(stack == NULL)
+ return;
+
+ memset(stack, 0x6b, THREAD_SIZE);
+}
+
+void check_stack_usage(struct thread_info *s)
+{
+ unsigned int *stack;
+ unsigned int *p, *end;
+ int left;
+
+ stack = (unsigned int *) (s + 1);
+ end = (unsigned int *) ((unsigned long) stack + THREAD_SIZE);
+ for(p = stack; p < end; p++){
+ if(*p != 0x6b6b6b6b){
+ left = (p - stack);
+ if(left < lowest_to_date){
+ printk("Greatest stack depth - %d bytes left\n",
+ left * sizeof(*p));
+ lowest_to_date = left;
+ }
+ return;
+ }
+ }
+}
+
+#endif
Index: linux-2.6.21-mm/include/asm-um/thread_info.h
===================================================================
--- linux-2.6.21-mm.orig/include/asm-um/thread_info.h 2007-05-09 14:34:39.000000000 -0400
+++ linux-2.6.21-mm/include/asm-um/thread_info.h 2007-05-09 14:36:10.000000000 -0400
@@ -52,6 +52,20 @@ static inline struct thread_info *curren
return ti;
}
+#ifdef CONFIG_STACK_USAGE
+
+extern void mark_stack(struct thread_info *stack);
+extern void check_stack_usage(struct thread_info *stack);
+
+#define alloc_thread_info(tsk) \
+ ({ struct thread_info *stack = kmalloc(THREAD_SIZE, GFP_KERNEL); \
+ mark_stack(stack); \
+ stack; \
+ })
+#define free_thread_info(ti) ({ check_stack_usage(ti) ; kfree(ti); })
+
+#else
+
/* thread information allocation */
#define alloc_thread_info(tsk) \
((struct thread_info *) kmalloc(THREAD_SIZE, GFP_KERNEL))
@@ -59,6 +73,8 @@ static inline struct thread_info *curren
#endif
+#endif
+
#define PREEMPT_ACTIVE 0x10000000
#define TIF_SYSCALL_TRACE 0 /* syscall trace active */
Index: linux-2.6.21-mm/arch/um/defconfig
===================================================================
--- linux-2.6.21-mm.orig/arch/um/defconfig 2007-05-09 14:42:04.000000000 -0400
+++ linux-2.6.21-mm/arch/um/defconfig 2007-05-09 14:42:59.000000000 -0400
@@ -527,3 +527,4 @@ CONFIG_FORCED_INLINING=y
# CONFIG_RCU_TORTURE_TEST is not set
# CONFIG_GPROF is not set
# CONFIG_GCOV is not set
+# CONFIG_STACK_USAGE is not set
-
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