commit 0c635450a6b0aca09742d8b514562592a3b315e5
Author: Andriy Gapon <avg@icyb.net.ua>
Date:   Thu May 17 20:03:22 2012 +0300

    [experiment] device_pager: use a hash table instead of plain list for objects

diff --git a/sys/vm/device_pager.c b/sys/vm/device_pager.c
index 99f561f..f0f1bd3 100644
--- a/sys/vm/device_pager.c
+++ b/sys/vm/device_pager.c
@@ -62,8 +62,6 @@ static void dev_pager_putpages(vm_object_t, vm_page_t *, int,
 static boolean_t dev_pager_haspage(vm_object_t, vm_pindex_t, int *,
 		int *);
 
-/* list of device pager objects */
-static struct pagerlst dev_pager_object_list;
 /* protect list manipulation */
 static struct mtx dev_pager_mtx;
 
@@ -96,10 +94,68 @@ static struct cdev_pager_ops old_dev_pager_ops = {
 	.cdev_pg_fault = old_dev_pager_fault
 };
 
+/* list of device pager objects */
+#define OBJECT_HTABLE_SIZE	256
+static struct pagerlst object_htable[OBJECT_HTABLE_SIZE];
+
+static u_int
+hash6432shift(uintptr_t key)
+{
+	key = (~key) + (key << 18);
+	key = key ^ (key >> 31);
+	key = key * 21;
+	key = key ^ (key >> 11);
+	key = key + (key << 6);
+	key = key ^ (key >> 22);
+	return (key);
+}
+
+static int
+hash_index(void *handle)
+{
+	return (hash6432shift((uintptr_t)handle) % OBJECT_HTABLE_SIZE);
+}
+
+static void
+object_list_insert(vm_object_t object)
+{
+	TAILQ_INSERT_TAIL(object_htable + hash_index(object->handle), object, pager_object_list);
+}
+
+static void
+object_list_remove(vm_object_t object)
+{
+	TAILQ_REMOVE(object_htable + hash_index(object->handle), object, pager_object_list);
+}
+
+static vm_object_t
+object_list_lookup(void *handle)
+{
+	struct pagerlst *pglist;
+	vm_object_t object;
+
+	pglist = object_htable + hash_index(handle);
+	TAILQ_FOREACH(object, pglist, pager_object_list) {
+		if (object->handle == handle) {
+			VM_OBJECT_LOCK(object);
+			if ((object->flags & OBJ_DEAD) == 0) {
+				vm_object_reference_locked(object);
+				VM_OBJECT_UNLOCK(object);
+				break;
+			}
+			VM_OBJECT_UNLOCK(object);
+		}
+	}
+	return (object);
+}
+
 static void
 dev_pager_init()
 {
-	TAILQ_INIT(&dev_pager_object_list);
+	int i;
+
+	for (i = 0; i < OBJECT_HTABLE_SIZE; i++)
+		TAILQ_INIT(&object_htable[i]);
 	mtx_init(&dev_pager_mtx, "dev_pager list", NULL, MTX_DEF);
 }
 
@@ -109,7 +165,7 @@ cdev_pager_lookup(void *handle)
 	vm_object_t object;
 
 	mtx_lock(&dev_pager_mtx);
-	object = vm_pager_object_lookup(&dev_pager_object_list, handle);
+	object = object_list_lookup(handle);
 	mtx_unlock(&dev_pager_mtx);
 	return (object);
 }
@@ -142,7 +198,7 @@ cdev_pager_allocate(void *handle, enum obj_type tp, struct cdev_pager_ops *ops,
 	 * Look up pager, creating as necessary.
 	 */
 	object1 = NULL;
-	object = vm_pager_object_lookup(&dev_pager_object_list, handle);
+	object = object_list_lookup(handle);
 	if (object == NULL) {
 		/*
 		 * Allocate object and associate it with the pager.  Initialize
@@ -157,7 +213,7 @@ cdev_pager_allocate(void *handle, enum obj_type tp, struct cdev_pager_ops *ops,
 		object1->un_pager.devp.ops = ops;
 		TAILQ_INIT(&object1->un_pager.devp.devp_pglist);
 		mtx_lock(&dev_pager_mtx);
-		object = vm_pager_object_lookup(&dev_pager_object_list, handle);
+		object = object_list_lookup(handle);
 		if (object != NULL) {
 			/*
 			 * We raced with other thread while allocating object.
@@ -168,8 +224,7 @@ cdev_pager_allocate(void *handle, enum obj_type tp, struct cdev_pager_ops *ops,
 			object = object1;
 			object1 = NULL;
 			object->handle = handle;
-			TAILQ_INSERT_TAIL(&dev_pager_object_list, object,
-			    pager_object_list);
+			object_list_insert(object);
 			KASSERT(object->type == tp,
 		("Inconsistent device pager type %p %d", object, tp));
 		}
@@ -181,8 +236,7 @@ cdev_pager_allocate(void *handle, enum obj_type tp, struct cdev_pager_ops *ops,
 	if (object1 != NULL) {
 		object1->handle = object1;
 		mtx_lock(&dev_pager_mtx);
-		TAILQ_INSERT_TAIL(&dev_pager_object_list, object1,
-		    pager_object_list);
+		object_list_insert(object1);
 		mtx_unlock(&dev_pager_mtx);
 		vm_object_deallocate(object1);
 	}
@@ -217,7 +271,7 @@ dev_pager_dealloc(object)
 	object->un_pager.devp.ops->cdev_pg_dtor(object->handle);
 
 	mtx_lock(&dev_pager_mtx);
-	TAILQ_REMOVE(&dev_pager_object_list, object, pager_object_list);
+	object_list_remove(object);
 	mtx_unlock(&dev_pager_mtx);
 	VM_OBJECT_LOCK(object);
 	/*