kern: remove the list of free stacks

* kern/counters.c: Remove relevant counters.
* kern/counters.h: Likewise.
* kern/thread.c (stack_free_{list,count,limit}): Drop variables.
(stack_next): Remove macro.
(stack_alloc_try): Allocate stack using the slab allocator.
(stack_alloc): Merely call `stack_alloc_try'.
(stack_free): Adopt accordingly.

3 files changed, 14 insertions, 137 deletions

diff --git a/kern/counters.c b/kern/counters.c
index 0a0665b..74fd42d 100644
--- a/kern/counters.c
+++ b/kern/counters.c
@@ -46,9 +46,6 @@ mach_counter_t c_stacks_current = 0;
 mach_counter_t c_stacks_max = 0;
 mach_counter_t c_stacks_min = 0;
 mach_counter_t c_stacks_total = 0;
-mach_counter_t c_stack_alloc_hits = 0;
-mach_counter_t c_stack_alloc_misses = 0;
-mach_counter_t c_stack_alloc_max = 0;
 mach_counter_t c_clock_ticks = 0;
 mach_counter_t c_ipc_mqueue_send_block = 0;
 mach_counter_t c_ipc_mqueue_receive_block_user = 0;
diff --git a/kern/counters.h b/kern/counters.h
index aa1e739..bfa9b44 100644
--- a/kern/counters.h
+++ b/kern/counters.h
@@ -69,9 +69,6 @@ extern mach_counter_t c_stacks_current;
 extern mach_counter_t c_stacks_max;
 extern mach_counter_t c_stacks_min;
 extern mach_counter_t c_stacks_total;
-extern mach_counter_t c_stack_alloc_hits;
-extern mach_counter_t c_stack_alloc_misses;
-extern mach_counter_t c_stack_alloc_max;
 extern mach_counter_t c_clock_ticks;
 extern mach_counter_t c_ipc_mqueue_send_block;
 extern mach_counter_t c_ipc_mqueue_receive_block_user;
diff --git a/kern/thread.c b/kern/thread.c
index 886d20d..5b51ec1 100644
--- a/kern/thread.c
+++ b/kern/thread.c
@@ -101,8 +101,6 @@ vm_size_t		stack_max_usage = 0;
  *		stack_free
  *		stack_handoff
  *		stack_collect
- *	and if MACH_DEBUG:
- *		stack_statistics
  */
 #else	/* MACHINE_STACK */
 /*
@@ -120,16 +118,10 @@ decl_simple_lock_data(, stack_lock_data)/* splsched only */
 #define stack_lock()	simple_lock(&stack_lock_data)
 #define stack_unlock()	simple_unlock(&stack_lock_data)
 
-vm_offset_t stack_free_list;		/* splsched only */
-unsigned int stack_free_count = 0;	/* splsched only */
-unsigned int stack_free_limit = 1;	/* patchable */
-
 /*
- *	The next field is at the base of the stack,
- *	so the low end is left unsullied.
+ * We allocate kernel stacks using the slab allocator.
  */
-
-#define stack_next(stack) (*((vm_offset_t *)((stack) + KERNEL_STACK_SIZE) - 1))
+static struct kmem_cache stack_cache;
 
 /*
  *	stack_alloc_try:
@@ -144,73 +136,37 @@ boolean_t stack_alloc_try(
 {
 	vm_offset_t stack;
 
-	stack_lock();
-	stack = stack_free_list;
-	if (stack != 0) {
-		stack_free_list = stack_next(stack);
-		stack_free_count--;
-	} else {
+	stack = kmem_cache_alloc(&stack_cache);
+	assert ((stack & (KERNEL_STACK_SIZE-1)) == 0);
+
+#if	MACH_DEBUG
+	if (stack)
+		stack_init(stack);
+#endif	/* MACH_DEBUG */
+	if (! stack)
 		stack = thread->stack_privilege;
-	}
-	stack_unlock();
 
 	if (stack != 0) {
 		stack_attach(thread, stack, resume);
-		counter(c_stack_alloc_hits++);
 		return TRUE;
 	} else {
-		counter(c_stack_alloc_misses++);
 		return FALSE;
 	}
 }
 
 /*
- * We allocate kernel stacks using the slab allocator.
- */
-static struct kmem_cache stack_cache;
-
-/*
  *	stack_alloc:
  *
  *	Allocate a kernel stack for a thread.
- *	May block.
  */
 
 kern_return_t stack_alloc(
 	thread_t	thread,
 	void		(*resume)(thread_t))
 {
-	vm_offset_t stack;
-	spl_t s;
-
-	/*
-	 *	We first try the free list.  It is probably empty,
-	 *	or stack_alloc_try would have succeeded, but possibly
-	 *	a stack was freed before the swapin thread got to us.
-	 */
-
-	s = splsched();
-	stack_lock();
-	stack = stack_free_list;
-	if (stack != 0) {
-		stack_free_list = stack_next(stack);
-		stack_free_count--;
-	}
-	stack_unlock();
-	(void) splx(s);
-
-	if (stack == 0) {
-		stack = kmem_cache_alloc(&stack_cache);
-		assert ((stack & (KERNEL_STACK_SIZE-1)) == 0);
-		if (stack == 0)
-			return KERN_RESOURCE_SHORTAGE;
-
-#if	MACH_DEBUG
-		stack_init(stack);
-#endif	/* MACH_DEBUG */
-	}
+	if (! stack_alloc_try (thread, resume))
+		return KERN_RESOURCE_SHORTAGE;
 
-	stack_attach(thread, stack, resume);
 	return KERN_SUCCESS;
 }
 
@@ -228,17 +184,8 @@ void stack_free(
 
 	stack = stack_detach(thread);
 
-	if (stack != thread->stack_privilege) {
-		stack_lock();
-		stack_next(stack) = stack_free_list;
-		stack_free_list = stack;
-		stack_free_count += 1;
-#if	MACH_COUNTERS
-		if (stack_free_count > c_stack_alloc_max)
-			c_stack_alloc_max = stack_free_count;
-#endif	/* MACH_COUNTERS */
-		stack_unlock();
-	}
+	if (stack != thread->stack_privilege)
+		kmem_cache_free (&stack_cache, stack);
 }
 
 /*
@@ -250,28 +197,6 @@ void stack_free(
 
 void stack_collect(void)
 {
-	vm_offset_t stack;
-	spl_t s;
-
-	s = splsched();
-	stack_lock();
-	while (stack_free_count > stack_free_limit) {
-		stack = stack_free_list;
-		stack_free_list = stack_next(stack);
-		stack_free_count--;
-		stack_unlock();
-		(void) splx(s);
-
-#if	MACH_DEBUG
-		stack_finalize(stack);
-#endif	/* MACH_DEBUG */
-		kmem_cache_free(&stack_cache, stack);
-
-		s = splsched();
-		stack_lock();
-	}
-	stack_unlock();
-	(void) splx(s);
 }
 #endif	/* MACHINE_STACK */
 
@@ -2383,46 +2308,6 @@ void stack_finalize(
 	}
 }
 
-#ifndef	MACHINE_STACK
-/*
- *	stack_statistics:
- *
- *	Return statistics on cached kernel stacks.
- *	*maxusagep must be initialized by the caller.
- */
-
-void stack_statistics(
-	natural_t *totalp,
-	vm_size_t *maxusagep)
-{
-	spl_t	s;
-
-	s = splsched();
-	stack_lock();
-	if (stack_check_usage) {
-		vm_offset_t stack;
-
-		/*
-		 *	This is pretty expensive to do at splsched,
-		 *	but it only happens when someone makes
-		 *	a debugging call, so it should be OK.
-		 */
-
-		for (stack = stack_free_list; stack != 0;
-		     stack = stack_next(stack)) {
-			vm_size_t usage = stack_usage(stack);
-
-			if (usage > *maxusagep)
-				*maxusagep = usage;
-		}
-	}
-
-	*totalp = stack_free_count;
-	stack_unlock();
-	(void) splx(s);
-}
-#endif	/* MACHINE_STACK */
-
 kern_return_t host_stack_usage(
 	host_t		host,
 	vm_size_t	*reservedp,
@@ -2442,8 +2327,6 @@ kern_return_t host_stack_usage(
 	maxusage = stack_max_usage;
 	simple_unlock(&stack_usage_lock);
 
-	stack_statistics(&total, &maxusage);
-
 	*reservedp = 0;
 	*totalp = total;
 	*spacep = *residentp = total * round_page(KERNEL_STACK_SIZE);