kern: allocate kernel stacks using the slab allocator

* kern/slab.c (kmem_cache_init): Relax alignment restriction.
* kern/thread.c (stack_cache): New variable.
(stack_alloc): Use the slab allocator.
(stack_collect): Adjust accordingly.
(thread_init): Initialize `stack_cache'.

1 files changed, 19 insertions, 10 deletions

diff --git a/kern/thread.c b/kern/thread.c
index b996559..3586e34 100644
--- a/kern/thread.c
+++ b/kern/thread.c
@@ -165,6 +165,11 @@ boolean_t stack_alloc_try(
 }
 
 /*
+ * We allocate kernel stacks using the slab allocator.
+ */
+static struct kmem_cache stack_cache;
+
+/*
  *	stack_alloc:
  *
  *	Allocate a kernel stack for a thread.
@@ -195,15 +200,10 @@ kern_return_t stack_alloc(
 	(void) splx(s);
 
 	if (stack == 0) {
-		kern_return_t kr;
-		/*
-		 *	Kernel stacks should be naturally aligned,
-		 *	so that it is easy to find the starting/ending
-		 *	addresses of a stack given an address in the middle.
-		 */
-		kr = kmem_alloc_aligned(kmem_map, &stack, KERNEL_STACK_SIZE);
-		if (kr != KERN_SUCCESS)
-			return kr;
+		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);
@@ -265,7 +265,7 @@ void stack_collect(void)
 #if	MACH_DEBUG
 		stack_finalize(stack);
 #endif	/* MACH_DEBUG */
-		kmem_free(kmem_map, stack, KERNEL_STACK_SIZE);
+		kmem_cache_free(&stack_cache, stack);
 
 		s = splsched();
 		stack_lock();
@@ -301,6 +301,15 @@ void thread_init(void)
 			NULL, NULL, NULL, 0);
 
 	/*
+	 *	Kernel stacks should be naturally aligned, so that it
+	 *	is easy to find the starting/ending addresses of a
+	 *	stack given an address in the middle.
+	 */
+	kmem_cache_init(&stack_cache, "stack",
+			KERNEL_STACK_SIZE, KERNEL_STACK_SIZE,
+			NULL, NULL, NULL, 0);
+
+	/*
 	 *	Fill in a template thread for fast initialization.
 	 *	[Fields that must be (or are typically) reset at
 	 *	time of creation are so noted.]