Although we perform path compression to reduce the height of the trie and

the number of interior nodes, we have previously created a level zero
interior node at the root of every non-empty trie, even when that node is
not strictly necessary, i.e., it has only one child.  This change is the
second (and final) step in eliminating those unnecessary level zero interior
nodes.  Specifically, it updates the deletion and insertion functions so
that they do not require a level zero interior node at the root of the trie.
For a "buildworld" workload, this change results in a 16.8% reduction in the
number of interior nodes allocated and a similar reduction in the average
execution time for lookup functions.  For example, the average execution
time for a call to vm_radix_lookup_ge() is reduced by 22.9%.

Reviewed by:	attilio, jeff (an earlier version)
Sponsored by:	EMC / Isilon Storage Division

1 files changed, 32 insertions, 26 deletions

diff --git a/sys/vm/vm_radix.c b/sys/vm/vm_radix.c
index 127079b..30869de 100644
--- a/sys/vm/vm_radix.c
+++ b/sys/vm/vm_radix.c
@@ -396,7 +396,8 @@ void
 vm_radix_insert(struct vm_radix *rtree, vm_page_t page)
 {
 	vm_pindex_t index, newind;
-	struct vm_radix_node *parent, *rnode, *tmp;
+	void **parentp;
+	struct vm_radix_node *rnode, *tmp;
 	vm_page_t m;
 	int slot;
 	uint16_t clev;
@@ -409,34 +410,34 @@ vm_radix_insert(struct vm_radix *rtree, vm_page_t page)
 	 */
 	rnode = vm_radix_getroot(rtree);
 	if (rnode == NULL) {
-		rnode = vm_radix_node_get(0, 1, 0);
-		vm_radix_setroot(rtree, rnode);
-		vm_radix_addpage(rnode, index, 0, page);
+		rtree->rt_root = (uintptr_t)page | VM_RADIX_ISLEAF;
 		return;
 	}
-	do {
-		slot = vm_radix_slot(index, rnode->rn_clev);
-		if (vm_radix_isleaf(rnode->rn_child[slot])) {
-			m = vm_radix_topage(rnode->rn_child[slot]);
+	parentp = (void **)&rtree->rt_root;
+	for (;;) {
+		if (vm_radix_isleaf(rnode)) {
+			m = vm_radix_topage(rnode);
 			if (m->pindex == index)
 				panic("%s: key %jx is already present",
 				    __func__, (uintmax_t)index);
 			clev = vm_radix_keydiff(m->pindex, index);
 			tmp = vm_radix_node_get(vm_radix_trimkey(index,
 			    clev - 1), 2, clev);
-			rnode->rn_child[slot] = tmp;
+			*parentp = tmp;
 			vm_radix_addpage(tmp, index, clev, page);
 			vm_radix_addpage(tmp, m->pindex, clev, m);
 			return;
-		}
+		} else if (vm_radix_keybarr(rnode, index))
+			break;
+		slot = vm_radix_slot(index, rnode->rn_clev);
 		if (rnode->rn_child[slot] == NULL) {
 			rnode->rn_count++;
 			vm_radix_addpage(rnode, index, rnode->rn_clev, page);
 			return;
 		}
-		parent = rnode;
+		parentp = &rnode->rn_child[slot];
 		rnode = rnode->rn_child[slot];
-	} while (!vm_radix_keybarr(rnode, index));
+	}
 
 	/*
 	 * A new node is needed because the right insertion level is reached.
@@ -447,7 +448,7 @@ vm_radix_insert(struct vm_radix *rtree, vm_page_t page)
 	clev = vm_radix_keydiff(newind, index);
 	tmp = vm_radix_node_get(vm_radix_trimkey(index, clev - 1), 2,
 	    clev);
-	parent->rn_child[slot] = tmp;
+	*parentp = tmp;
 	vm_radix_addpage(tmp, index, clev, page);
 	slot = vm_radix_slot(newind, clev);
 	tmp->rn_child[slot] = rnode;
@@ -694,8 +695,15 @@ vm_radix_remove(struct vm_radix *rtree, vm_pindex_t index)
 	vm_page_t m;
 	int i, slot;
 
-	parent = NULL;
 	rnode = vm_radix_getroot(rtree);
+	if (vm_radix_isleaf(rnode)) {
+		m = vm_radix_topage(rnode);
+		if (m->pindex != index)
+			panic("%s: invalid key found", __func__);
+		vm_radix_setroot(rtree, NULL);
+		return;
+	}
+	parent = NULL;
 	for (;;) {
 		if (rnode == NULL)
 			panic("vm_radix_remove: impossible to locate the key");
@@ -708,22 +716,19 @@ vm_radix_remove(struct vm_radix *rtree, vm_pindex_t index)
 			rnode->rn_count--;
 			if (rnode->rn_count > 1)
 				break;
-			if (parent == NULL) {
-				if (rnode->rn_count == 0) {
-					vm_radix_node_put(rnode);
-					vm_radix_setroot(rtree, NULL);
-				}
-				break;
-			}
 			for (i = 0; i < VM_RADIX_COUNT; i++)
 				if (rnode->rn_child[i] != NULL)
 					break;
 			KASSERT(i != VM_RADIX_COUNT,
 			    ("%s: invalid node configuration", __func__));
-			slot = vm_radix_slot(index, parent->rn_clev);
-			KASSERT(parent->rn_child[slot] == rnode,
-			    ("%s: invalid child value", __func__));
-			parent->rn_child[slot] = rnode->rn_child[i];
+			if (parent == NULL)
+				vm_radix_setroot(rtree, rnode->rn_child[i]);
+			else {
+				slot = vm_radix_slot(index, parent->rn_clev);
+				KASSERT(parent->rn_child[slot] == rnode,
+				    ("%s: invalid child value", __func__));
+				parent->rn_child[slot] = rnode->rn_child[i];
+			}
 			rnode->rn_count--;
 			rnode->rn_child[i] = NULL;
 			vm_radix_node_put(rnode);
@@ -748,7 +753,8 @@ vm_radix_reclaim_allnodes(struct vm_radix *rtree)
 	if (root == NULL)
 		return;
 	vm_radix_setroot(rtree, NULL);
-	vm_radix_reclaim_allnodes_int(root);
+	if (!vm_radix_isleaf(root))
+		vm_radix_reclaim_allnodes_int(root);
 }
 
 #ifdef DDB