Revert "radix_trie: have vm_radix use pctrie code"

This reverts commit a494d30465f21e8cb014a5c788a43001397325d7.

3 files changed, 709 insertions, 109 deletions

diff --git a/sys/vm/_vm_radix.h b/sys/vm/_vm_radix.h
index 2d9b05c7b52a..01eb25a9dccf 100644
--- a/sys/vm/_vm_radix.h
+++ b/sys/vm/_vm_radix.h
@@ -31,13 +31,16 @@
 #ifndef __VM_RADIX_H_
 #define __VM_RADIX_H_
 
-#include <sys/_pctrie.h>
+/*
+ * Radix tree node.
+ */
+struct vm_radix_node;
 
 /*
- * Radix tree
+ * Radix tree root.
  */
 struct vm_radix {
-	struct pctrie	rt_trie;
+	struct vm_radix_node	*rt_root;
 };
 
 #endif /* !__VM_RADIX_H_ */
diff --git a/sys/vm/vm_radix.c b/sys/vm/vm_radix.c
index b8c693eca66f..768a56ed76f7 100644
--- a/sys/vm/vm_radix.c
+++ b/sys/vm/vm_radix.c
@@ -54,26 +54,302 @@
 #include "opt_ddb.h"
 
 #include <sys/param.h>
-#include <sys/pctrie.h>
+#include <sys/systm.h>
+#include <sys/kernel.h>
+#include <sys/libkern.h>
+#include <sys/proc.h>
+#include <sys/vmmeter.h>
+#include <sys/smr.h>
+#include <sys/smr_types.h>
 
 #include <vm/uma.h>
 #include <vm/vm.h>
+#include <vm/vm_param.h>
+#include <vm/vm_object.h>
 #include <vm/vm_page.h>
 #include <vm/vm_radix.h>
 
+#ifdef DDB
+#include <ddb/ddb.h>
+#endif
+
+/*
+ * These widths should allow the pointers to a node's children to fit within
+ * a single cache line.  The extra levels from a narrow width should not be
+ * a problem thanks to path compression.
+ */
+#ifdef __LP64__
+#define	VM_RADIX_WIDTH	4
+#else
+#define	VM_RADIX_WIDTH	3
+#endif
+
+#define	VM_RADIX_COUNT	(1 << VM_RADIX_WIDTH)
+#define	VM_RADIX_MASK	(VM_RADIX_COUNT - 1)
+#define	VM_RADIX_LIMIT							\
+	(howmany(sizeof(vm_pindex_t) * NBBY, VM_RADIX_WIDTH) - 1)
+
+#if VM_RADIX_WIDTH == 3
+typedef uint8_t rn_popmap_t;
+#elif VM_RADIX_WIDTH == 4
+typedef uint16_t rn_popmap_t;
+#elif VM_RADIX_WIDTH == 5
+typedef uint32_t rn_popmap_t;
+#else
+#error Unsupported width
+#endif
+_Static_assert(sizeof(rn_popmap_t) <= sizeof(int),
+    "rn_popmap_t too wide");
+
+/* Set of all flag bits stored in node pointers. */
+#define	VM_RADIX_FLAGS	(VM_RADIX_ISLEAF)
+#define	VM_RADIX_PAD	VM_RADIX_FLAGS
+
+enum vm_radix_access { SMR, LOCKED, UNSERIALIZED };
+
+struct vm_radix_node;
+typedef SMR_POINTER(struct vm_radix_node *) smrnode_t;
+
+struct vm_radix_node {
+	vm_pindex_t	rn_owner;			/* Owner of record. */
+	rn_popmap_t	rn_popmap;			/* Valid children. */
+	uint8_t		rn_clev;			/* Level * WIDTH. */
+	smrnode_t	rn_child[VM_RADIX_COUNT];	/* Child nodes. */
+};
+
 static uma_zone_t vm_radix_node_zone;
-smr_t vm_radix_smr;
+static smr_t vm_radix_smr;
+
+static void vm_radix_node_store(smrnode_t *p, struct vm_radix_node *v,
+    enum vm_radix_access access);
 
-void *
-vm_radix_node_alloc(struct pctrie *ptree)
+/*
+ * Map index to an array position for the children of rnode,
+ */
+static __inline int
+vm_radix_slot(struct vm_radix_node *rnode, vm_pindex_t index)
 {
-	return (uma_zalloc_smr(vm_radix_node_zone, M_NOWAIT));
+	return ((index >> rnode->rn_clev) & VM_RADIX_MASK);
 }
 
-void
-vm_radix_node_free(struct pctrie *ptree, void *node)
+/*
+ * Returns true if index does not belong to the specified rnode.  Otherwise,
+ * sets slot value, and returns false.
+ */
+static __inline bool
+vm_radix_keybarr(struct vm_radix_node *rnode, vm_pindex_t index, int *slot)
+{
+	index = (index - rnode->rn_owner) >> rnode->rn_clev;
+	if (index >= VM_RADIX_COUNT)
+		return (true);
+	*slot = index;
+	return (false);
+}
+
+/*
+ * Allocate a radix node.
+ */
+static struct vm_radix_node *
+vm_radix_node_get(vm_pindex_t index, vm_pindex_t newind)
+{
+	struct vm_radix_node *rnode;
+
+	rnode = uma_zalloc_smr(vm_radix_node_zone, M_NOWAIT);
+	if (rnode == NULL)
+		return (NULL);
+
+	/*
+	 * We want to clear the last child pointer after the final section
+	 * has exited so lookup can not return false negatives.  It is done
+	 * here because it will be cache-cold in the dtor callback.
+	 */
+	if (rnode->rn_popmap != 0) {
+		vm_radix_node_store(&rnode->rn_child[ffs(rnode->rn_popmap) - 1],
+		    VM_RADIX_NULL, UNSERIALIZED);
+		rnode->rn_popmap = 0;
+	}
+
+	/*
+	 * From the highest-order bit where the indexes differ,
+	 * compute the highest level in the trie where they differ.  Then,
+	 * compute the least index of this subtrie.
+	 */
+	KASSERT(index != newind, ("%s: passing the same key value %jx",
+	    __func__, (uintmax_t)index));
+	_Static_assert(sizeof(long long) >= sizeof(vm_pindex_t),
+	    "vm_pindex_t too wide");
+	_Static_assert(sizeof(vm_pindex_t) * NBBY <=
+	    (1 << (sizeof(rnode->rn_clev) * NBBY)), "rn_clev too narrow");
+	rnode->rn_clev = rounddown(flsll(index ^ newind) - 1, VM_RADIX_WIDTH);
+	rnode->rn_owner = VM_RADIX_COUNT;
+	rnode->rn_owner = index & -(rnode->rn_owner << rnode->rn_clev);
+	return (rnode);
+}
+
+/*
+ * Free radix node.
+ */
+static __inline void
+vm_radix_node_put(struct vm_radix_node *rnode)
+{
+#ifdef INVARIANTS
+	int slot;
+
+	KASSERT(powerof2(rnode->rn_popmap),
+	    ("vm_radix_node_put: rnode %p has too many children %04x", rnode,
+	    rnode->rn_popmap));
+	for (slot = 0; slot < VM_RADIX_COUNT; slot++) {
+		if ((rnode->rn_popmap & (1 << slot)) != 0)
+			continue;
+		KASSERT(smr_unserialized_load(&rnode->rn_child[slot], true) ==
+		    VM_RADIX_NULL,
+		    ("vm_radix_node_put: rnode %p has a child", rnode));
+	}
+#endif
+	uma_zfree_smr(vm_radix_node_zone, rnode);
+}
+
+/*
+ * Fetch a node pointer from a slot in another node.
+ */
+static __inline struct vm_radix_node *
+vm_radix_node_load(smrnode_t *p, enum vm_radix_access access)
+{
+
+	switch (access) {
+	case UNSERIALIZED:
+		return (smr_unserialized_load(p, true));
+	case LOCKED:
+		return (smr_serialized_load(p, true));
+	case SMR:
+		return (smr_entered_load(p, vm_radix_smr));
+	}
+	__assert_unreachable();
+}
+
+static __inline void
+vm_radix_node_store(smrnode_t *p, struct vm_radix_node *v,
+    enum vm_radix_access access)
+{
+
+	switch (access) {
+	case UNSERIALIZED:
+		smr_unserialized_store(p, v, true);
+		break;
+	case LOCKED:
+		smr_serialized_store(p, v, true);
+		break;
+	case SMR:
+		panic("vm_radix_node_store: Not supported in smr section.");
+	}
+}
+
+/*
+ * Get the root node for a radix tree.
+ */
+static __inline struct vm_radix_node *
+vm_radix_root_load(struct vm_radix *rtree, enum vm_radix_access access)
+{
+
+	return (vm_radix_node_load((smrnode_t *)&rtree->rt_root, access));
+}
+
+/*
+ * Set the root node for a radix tree.
+ */
+static __inline void
+vm_radix_root_store(struct vm_radix *rtree, struct vm_radix_node *rnode,
+    enum vm_radix_access access)
+{
+
+	vm_radix_node_store((smrnode_t *)&rtree->rt_root, rnode, access);
+}
+
+/*
+ * Returns TRUE if the specified radix node is a leaf and FALSE otherwise.
+ */
+static __inline bool
+vm_radix_isleaf(struct vm_radix_node *rnode)
+{
+
+	return (((uintptr_t)rnode & VM_RADIX_ISLEAF) != 0);
+}
+
+/*
+ * Returns page cast to radix node with leaf bit set.
+ */
+static __inline struct vm_radix_node *
+vm_radix_toleaf(vm_page_t page)
+{
+	return ((struct vm_radix_node *)((uintptr_t)page | VM_RADIX_ISLEAF));
+}
+
+/*
+ * Returns the associated page extracted from rnode.
+ */
+static __inline vm_page_t
+vm_radix_topage(struct vm_radix_node *rnode)
+{
+
+	return ((vm_page_t)((uintptr_t)rnode & ~VM_RADIX_FLAGS));
+}
+
+/*
+ * Make 'child' a child of 'rnode'.
+ */
+static __inline void
+vm_radix_addnode(struct vm_radix_node *rnode, vm_pindex_t index,
+    struct vm_radix_node *child, enum vm_radix_access access)
+{
+	int slot;
+
+	slot = vm_radix_slot(rnode, index);
+	vm_radix_node_store(&rnode->rn_child[slot], child, access);
+	rnode->rn_popmap ^= 1 << slot;
+	KASSERT((rnode->rn_popmap & (1 << slot)) != 0,
+	    ("%s: bad popmap slot %d in rnode %p", __func__, slot, rnode));
+}
+
+/*
+ * Internal helper for vm_radix_reclaim_allnodes().
+ * This function is recursive.
+ */
+static void
+vm_radix_reclaim_allnodes_int(struct vm_radix_node *rnode)
+{
+	struct vm_radix_node *child;
+	int slot;
+
+	while (rnode->rn_popmap != 0) {
+		slot = ffs(rnode->rn_popmap) - 1;
+		child = vm_radix_node_load(&rnode->rn_child[slot],
+		    UNSERIALIZED);
+		KASSERT(child != VM_RADIX_NULL,
+		    ("%s: bad popmap slot %d in rnode %p",
+		    __func__, slot, rnode));
+		if (!vm_radix_isleaf(child))
+			vm_radix_reclaim_allnodes_int(child);
+		rnode->rn_popmap ^= 1 << slot;
+		vm_radix_node_store(&rnode->rn_child[slot], VM_RADIX_NULL,
+		    UNSERIALIZED);
+	}
+	vm_radix_node_put(rnode);
+}
+
+/*
+ * radix node zone initializer.
+ */
+static int
+vm_radix_zone_init(void *mem, int size, int flags)
 {
-	uma_zfree_smr(vm_radix_node_zone, node);
+	struct vm_radix_node *rnode;
+
+	rnode = mem;
+	rnode->rn_popmap = 0;
+	for (int i = 0; i < nitems(rnode->rn_child); i++)
+		vm_radix_node_store(&rnode->rn_child[i], VM_RADIX_NULL,
+		    UNSERIALIZED);
+	return (0);
 }
 
 #ifndef UMA_MD_SMALL_ALLOC
@@ -107,14 +383,412 @@ void
 vm_radix_zinit(void)
 {
 
-	vm_radix_node_zone = uma_zcreate("RADIX NODE", pctrie_node_size(),
-	    NULL, NULL, pctrie_zone_init, NULL,
-	    PCTRIE_PAD, UMA_ZONE_VM | UMA_ZONE_SMR);
+	vm_radix_node_zone = uma_zcreate("RADIX NODE",
+	    sizeof(struct vm_radix_node), NULL, NULL, vm_radix_zone_init, NULL,
+	    VM_RADIX_PAD, UMA_ZONE_VM | UMA_ZONE_SMR);
 	vm_radix_smr = uma_zone_get_smr(vm_radix_node_zone);
 }
 
+/*
+ * Inserts the key-value pair into the trie.
+ * Panics if the key already exists.
+ */
+int
+vm_radix_insert(struct vm_radix *rtree, vm_page_t page)
+{
+	vm_pindex_t index, newind;
+	struct vm_radix_node *leaf, *parent, *rnode;
+	smrnode_t *parentp;
+	int slot;
+
+	index = page->pindex;
+	leaf = vm_radix_toleaf(page);
+
+	/*
+	 * The owner of record for root is not really important because it
+	 * will never be used.
+	 */
+	rnode = vm_radix_root_load(rtree, LOCKED);
+	parent = NULL;
+	for (;;) {
+		if (vm_radix_isleaf(rnode)) {
+			if (rnode == VM_RADIX_NULL) {
+				if (parent == NULL)
+					rtree->rt_root = leaf;
+				else
+					vm_radix_addnode(parent, index, leaf,
+					    LOCKED);
+				return (0);
+			}
+			newind = vm_radix_topage(rnode)->pindex;
+			if (newind == index)
+				panic("%s: key %jx is already present",
+				    __func__, (uintmax_t)index);
+			break;
+		}
+		if (vm_radix_keybarr(rnode, index, &slot)) {
+			newind = rnode->rn_owner;
+			break;
+		}
+		parent = rnode;
+		rnode = vm_radix_node_load(&rnode->rn_child[slot], LOCKED);
+	}
+
+	/*
+	 * A new node is needed because the right insertion level is reached.
+	 * Setup the new intermediate node and add the 2 children: the
+	 * new object and the older edge or object.
+	 */
+	parentp = (parent != NULL) ? &parent->rn_child[slot]:
+	    (smrnode_t *)&rtree->rt_root;
+	parent = vm_radix_node_get(index, newind);
+	if (parent == NULL)
+		return (ENOMEM);
+	/* These writes are not yet visible due to ordering. */
+	vm_radix_addnode(parent, index, leaf, UNSERIALIZED);
+	vm_radix_addnode(parent, newind, rnode, UNSERIALIZED);
+	/* Serializing write to make the above visible. */
+	vm_radix_node_store(parentp, parent, LOCKED);
+	return (0);
+}
+
+/*
+ * Returns the value stored at the index.  If the index is not present,
+ * NULL is returned.
+ */
+static __always_inline vm_page_t
+_vm_radix_lookup(struct vm_radix *rtree, vm_pindex_t index,
+    enum vm_radix_access access)
+{
+	struct vm_radix_node *rnode;
+	vm_page_t m;
+	int slot;
+
+	rnode = vm_radix_root_load(rtree, access);
+	for (;;) {
+		if (vm_radix_isleaf(rnode)) {
+			if ((m = vm_radix_topage(rnode)) != NULL &&
+			    m->pindex == index)
+				return (m);
+			break;
+		}
+		if (vm_radix_keybarr(rnode, index, &slot))
+			break;
+		rnode = vm_radix_node_load(&rnode->rn_child[slot], access);
+	}
+	return (NULL);
+}
+
+/*
+ * Returns the value stored at the index assuming there is an external lock.
+ *
+ * If the index is not present, NULL is returned.
+ */
+vm_page_t
+vm_radix_lookup(struct vm_radix *rtree, vm_pindex_t index)
+{
+
+	return _vm_radix_lookup(rtree, index, LOCKED);
+}
+
+/*
+ * Returns the value stored at the index without requiring an external lock.
+ *
+ * If the index is not present, NULL is returned.
+ */
+vm_page_t
+vm_radix_lookup_unlocked(struct vm_radix *rtree, vm_pindex_t index)
+{
+	vm_page_t m;
+
+	smr_enter(vm_radix_smr);
+	m = _vm_radix_lookup(rtree, index, SMR);
+	smr_exit(vm_radix_smr);
+
+	return (m);
+}
+
+/*
+ * Returns the page with the least pindex that is greater than or equal to the
+ * specified pindex, or NULL if there are no such pages.
+ *
+ * Requires that access be externally synchronized by a lock.
+ */
+vm_page_t
+vm_radix_lookup_ge(struct vm_radix *rtree, vm_pindex_t index)
+{
+	struct vm_radix_node *rnode, *succ;
+	vm_page_t m;
+	int slot;
+
+	/*
+	 * Descend the trie as if performing an ordinary lookup for the page
+	 * with the specified pindex.  However, unlike an ordinary lookup, as we
+	 * descend the trie, we use "succ" to remember the last branching-off
+	 * point, that is, the interior node under which the page with the least
+	 * pindex that is both outside our current path down the trie and more
+	 * than the specified pindex resides.  (The node's popmap makes it fast
+	 * and easy to recognize a branching-off point.)  If our ordinary lookup
+	 * fails to yield a page with a pindex that is greater than or equal to
+	 * the specified pindex, then we will exit this loop and perform a
+	 * lookup starting from "succ".  If "succ" is not NULL, then that lookup
+	 * is guaranteed to succeed.
+	 */
+	rnode = vm_radix_root_load(rtree, LOCKED);
+	succ = NULL;
+	for (;;) {
+		if (vm_radix_isleaf(rnode)) {
+			if ((m = vm_radix_topage(rnode)) != NULL &&
+			    m->pindex >= index)
+				return (m);
+			break;
+		}
+		if (vm_radix_keybarr(rnode, index, &slot)) {
+			/*
+			 * If all pages in this subtree have pindex > index,
+			 * then the page in this subtree with the least pindex
+			 * is the answer.
+			 */
+			if (rnode->rn_owner > index)
+				succ = rnode;
+			break;
+		}
+
+		/*
+		 * Just in case the next search step leads to a subtree of all
+		 * pages with pindex < index, check popmap to see if a next
+		 * bigger step, to a subtree of all pages with pindex > index,
+		 * is available.  If so, remember to restart the search here.
+		 */
+		if ((rnode->rn_popmap >> slot) > 1)
+			succ = rnode;
+		rnode = vm_radix_node_load(&rnode->rn_child[slot], LOCKED);
+	}
+
+	/*
+	 * Restart the search from the last place visited in the subtree that
+	 * included some pages with pindex > index, if there was such a place.
+	 */
+	if (succ == NULL)
+		return (NULL);
+	if (succ != rnode) {
+		/*
+		 * Take a step to the next bigger sibling of the node chosen
+		 * last time.  In that subtree, all pages have pindex > index.
+		 */
+		slot = vm_radix_slot(succ, index) + 1;
+		KASSERT((succ->rn_popmap >> slot) != 0,
+		    ("%s: no popmap siblings past slot %d in node %p",
+		    __func__, slot, succ));
+		slot += ffs(succ->rn_popmap >> slot) - 1;
+		succ = vm_radix_node_load(&succ->rn_child[slot], LOCKED);
+	}
+
+	/*
+	 * Find the page in the subtree rooted at "succ" with the least pindex.
+	 */
+	while (!vm_radix_isleaf(succ)) {
+		KASSERT(succ->rn_popmap != 0,
+		    ("%s: no popmap children in node %p",  __func__, succ));
+		slot = ffs(succ->rn_popmap) - 1;
+		succ = vm_radix_node_load(&succ->rn_child[slot], LOCKED);
+	}
+	return (vm_radix_topage(succ));
+}
+
+/*
+ * Returns the page with the greatest pindex that is less than or equal to the
+ * specified pindex, or NULL if there are no such pages.
+ *
+ * Requires that access be externally synchronized by a lock.
+ */
+vm_page_t
+vm_radix_lookup_le(struct vm_radix *rtree, vm_pindex_t index)
+{
+	struct vm_radix_node *pred, *rnode;
+	vm_page_t m;
+	int slot;
+
+	/*
+	 * Mirror the implementation of vm_radix_lookup_ge, described above.
+	 */
+	rnode = vm_radix_root_load(rtree, LOCKED);
+	pred = NULL;
+	for (;;) {
+		if (vm_radix_isleaf(rnode)) {
+			if ((m = vm_radix_topage(rnode)) != NULL &&
+			    m->pindex <= index)
+				return (m);
+			break;
+		}
+		if (vm_radix_keybarr(rnode, index, &slot)) {
+			if (rnode->rn_owner < index)
+				pred = rnode;
+			break;
+		}
+		if ((rnode->rn_popmap & ((1 << slot) - 1)) != 0)
+			pred = rnode;
+		rnode = vm_radix_node_load(&rnode->rn_child[slot], LOCKED);
+	}
+	if (pred == NULL)
+		return (NULL);
+	if (pred != rnode) {
+		slot = vm_radix_slot(pred, index);
+		KASSERT((pred->rn_popmap & ((1 << slot) - 1)) != 0,
+		    ("%s: no popmap siblings before slot %d in node %p",
+		    __func__, slot, pred));
+		slot = fls(pred->rn_popmap & ((1 << slot) - 1)) - 1;
+		pred = vm_radix_node_load(&pred->rn_child[slot], LOCKED);
+	}
+	while (!vm_radix_isleaf(pred)) {
+		KASSERT(pred->rn_popmap != 0,
+		    ("%s: no popmap children in node %p",  __func__, pred));
+		slot = fls(pred->rn_popmap) - 1;
+		pred = vm_radix_node_load(&pred->rn_child[slot], LOCKED);
+	}
+	return (vm_radix_topage(pred));
+}
+
+/*
+ * Remove the specified index from the trie, and return the value stored at
+ * that index.  If the index is not present, return NULL.
+ */
+vm_page_t
+vm_radix_remove(struct vm_radix *rtree, vm_pindex_t index)
+{
+	struct vm_radix_node *child, *parent, *rnode;
+	vm_page_t m;
+	int slot;
+
+	rnode = NULL;
+	child = vm_radix_root_load(rtree, LOCKED);
+	for (;;) {
+		if (vm_radix_isleaf(child))
+			break;
+		parent = rnode;
+		rnode = child;
+		slot = vm_radix_slot(rnode, index);
+		child = vm_radix_node_load(&rnode->rn_child[slot], LOCKED);
+	}
+	if ((m = vm_radix_topage(child)) == NULL || m->pindex != index)
+		return (NULL);
+	if (rnode == NULL) {
+		vm_radix_root_store(rtree, VM_RADIX_NULL, LOCKED);
+		return (m);
+	}
+	KASSERT((rnode->rn_popmap & (1 << slot)) != 0,
+	    ("%s: bad popmap slot %d in rnode %p", __func__, slot, rnode));
+	rnode->rn_popmap ^= 1 << slot;
+	vm_radix_node_store(&rnode->rn_child[slot], VM_RADIX_NULL, LOCKED);
+	if (!powerof2(rnode->rn_popmap))
+		return (m);
+	KASSERT(rnode->rn_popmap != 0, ("%s: bad popmap all zeroes", __func__));
+	slot = ffs(rnode->rn_popmap) - 1;
+	child = vm_radix_node_load(&rnode->rn_child[slot], LOCKED);
+	KASSERT(child != VM_RADIX_NULL,
+	    ("%s: bad popmap slot %d in rnode %p", __func__, slot, rnode));
+	if (parent == NULL)
+		vm_radix_root_store(rtree, child, LOCKED);
+	else {
+		slot = vm_radix_slot(parent, index);
+		KASSERT(rnode ==
+		    vm_radix_node_load(&parent->rn_child[slot], LOCKED),
+		    ("%s: invalid child value", __func__));
+		vm_radix_node_store(&parent->rn_child[slot], child, LOCKED);
+	}
+	/*
+	 * The child is still valid and we can not zero the
+	 * pointer until all smr references are gone.
+	 */
+	vm_radix_node_put(rnode);
+	return (m);
+}
+
+/*
+ * Remove and free all the nodes from the radix tree.
+ * This function is recursive but there is a tight control on it as the
+ * maximum depth of the tree is fixed.
+ */
+void
+vm_radix_reclaim_allnodes(struct vm_radix *rtree)
+{
+	struct vm_radix_node *root;
+
+	root = vm_radix_root_load(rtree, LOCKED);
+	if (root == VM_RADIX_NULL)
+		return;
+	vm_radix_root_store(rtree, VM_RADIX_NULL, UNSERIALIZED);
+	if (!vm_radix_isleaf(root))
+		vm_radix_reclaim_allnodes_int(root);
+}
+
+/*
+ * Replace an existing page in the trie with another one.
+ * Panics if there is not an old page in the trie at the new page's index.
+ */
+vm_page_t
+vm_radix_replace(struct vm_radix *rtree, vm_page_t newpage)
+{
+	struct vm_radix_node *leaf, *parent, *rnode;
+	vm_page_t m;
+	vm_pindex_t index;
+	int slot;
+
+	leaf = vm_radix_toleaf(newpage);
+	index = newpage->pindex;
+	rnode = vm_radix_root_load(rtree, LOCKED);
+	parent = NULL;
+	for (;;) {
+		if (vm_radix_isleaf(rnode)) {
+			if ((m = vm_radix_topage(rnode)) != NULL &&
+			    m->pindex == index) {
+				if (parent == NULL)
+					rtree->rt_root = leaf;
+				else
+					vm_radix_node_store(
+					    &parent->rn_child[slot], leaf,
+					    LOCKED);
+				return (m);
+			}
+			break;
+		}
+		if (vm_radix_keybarr(rnode, index, &slot))
+			break;
+		parent = rnode;
+		rnode = vm_radix_node_load(&rnode->rn_child[slot], LOCKED);
+	}
+	panic("%s: original replacing page not found", __func__);
+}
+
 void
 vm_radix_wait(void)
 {
 	uma_zwait(vm_radix_node_zone);
 }
+
+#ifdef DDB
+/*
+ * Show details about the given radix node.
+ */
+DB_SHOW_COMMAND(radixnode, db_show_radixnode)
+{
+	struct vm_radix_node *rnode, *tmp;
+	int slot;
+	rn_popmap_t popmap;
+
+        if (!have_addr)
+                return;
+	rnode = (struct vm_radix_node *)addr;
+	db_printf("radixnode %p, owner %jx, children popmap %04x, level %u:\n",
+	    (void *)rnode, (uintmax_t)rnode->rn_owner, rnode->rn_popmap,
+	    rnode->rn_clev / VM_RADIX_WIDTH);
+	for (popmap = rnode->rn_popmap; popmap != 0; popmap ^= 1 << slot) {
+		slot = ffs(popmap) - 1;
+		tmp = vm_radix_node_load(&rnode->rn_child[slot], UNSERIALIZED);
+		db_printf("slot: %d, val: %p, page: %p, clev: %d\n",
+		    slot, (void *)tmp,
+		    vm_radix_isleaf(tmp) ?  vm_radix_topage(tmp) : NULL,
+		    rnode->rn_clev / VM_RADIX_WIDTH);
+	}
+}
+#endif /* DDB */
diff --git a/sys/vm/vm_radix.h b/sys/vm/vm_radix.h
index a332618fc0e6..231edda65102 100644
--- a/sys/vm/vm_radix.h
+++ b/sys/vm/vm_radix.h
@@ -34,113 +34,36 @@
 #include <vm/_vm_radix.h>
 
 #ifdef _KERNEL
-#include <sys/pctrie.h>
-#include <vm/vm.h>
 
+int		vm_radix_insert(struct vm_radix *rtree, vm_page_t page);
 void		vm_radix_wait(void);
+vm_page_t	vm_radix_lookup(struct vm_radix *rtree, vm_pindex_t index);
+vm_page_t	vm_radix_lookup_ge(struct vm_radix *rtree, vm_pindex_t index);
+vm_page_t	vm_radix_lookup_le(struct vm_radix *rtree, vm_pindex_t index);
+vm_page_t	vm_radix_lookup_unlocked(struct vm_radix *rtree, vm_pindex_t index);
+void		vm_radix_reclaim_allnodes(struct vm_radix *rtree);
+vm_page_t	vm_radix_remove(struct vm_radix *rtree, vm_pindex_t index);
+vm_page_t	vm_radix_replace(struct vm_radix *rtree, vm_page_t newpage);
 void		vm_radix_zinit(void);
-void		*vm_radix_node_alloc(struct pctrie *ptree);
-void		vm_radix_node_free(struct pctrie *ptree, void *node);
-extern smr_t	vm_radix_smr;
-
-static __inline void
-vm_radix_init(struct vm_radix *rtree)
-{
-	pctrie_init(&rtree->rt_trie);
-}
-
-static __inline bool
-vm_radix_is_empty(struct vm_radix *rtree)
-{
-	return (pctrie_is_empty(&rtree->rt_trie));
-}
-
-PCTRIE_DEFINE_SMR(VM_RADIX, vm_page, pindex, vm_radix_node_alloc, vm_radix_node_free,
-    vm_radix_smr);
 
 /*
- * Inserts the key-value pair into the trie.
- * Panics if the key already exists.
+ * Each search path in the trie terminates at a leaf, which is a pointer to a
+ * page marked with a set 1-bit.  A leaf may be associated with a null pointer
+ * to indicate no page there.
  */
-static __inline int
-vm_radix_insert(struct vm_radix *rtree, vm_page_t page)
-{
-	return (VM_RADIX_PCTRIE_INSERT(&rtree->rt_trie, page));
-}
-
-/*
- * Returns the value stored at the index assuming there is an external lock.
- *
- * If the index is not present, NULL is returned.
- */
-static __inline vm_page_t
-vm_radix_lookup(struct vm_radix *rtree, vm_pindex_t index)
-{
-	return (VM_RADIX_PCTRIE_LOOKUP(&rtree->rt_trie, index));
-}
-
-/*
- * Returns the value stored at the index without requiring an external lock.
- *
- * If the index is not present, NULL is returned.
- */
-static __inline vm_page_t
-vm_radix_lookup_unlocked(struct vm_radix *rtree, vm_pindex_t index)
-{
-	return (VM_RADIX_PCTRIE_LOOKUP_UNLOCKED(&rtree->rt_trie, index));
-}
+#define	VM_RADIX_ISLEAF	0x1
+#define VM_RADIX_NULL (struct vm_radix_node *)VM_RADIX_ISLEAF
 
-/*
- * Returns the page with the least pindex that is greater than or equal to the
- * specified pindex, or NULL if there are no such pages.
- *
- * Requires that access be externally synchronized by a lock.
- */
-static __inline vm_page_t
-vm_radix_lookup_ge(struct vm_radix *rtree, vm_pindex_t index)
-{
-	return (VM_RADIX_PCTRIE_LOOKUP_GE(&rtree->rt_trie, index));
-}
-
-/*
- * Returns the page with the greatest pindex that is less than or equal to the
- * specified pindex, or NULL if there are no such pages.
- *
- * Requires that access be externally synchronized by a lock.
- */
-static __inline vm_page_t
-vm_radix_lookup_le(struct vm_radix *rtree, vm_pindex_t index)
-{
-	return (VM_RADIX_PCTRIE_LOOKUP_LE(&rtree->rt_trie, index));
-}
-
-/*
- * Remove the specified index from the trie, and return the value stored at
- * that index.  If the index is not present, return NULL.
- */
-static __inline vm_page_t
-vm_radix_remove(struct vm_radix *rtree, vm_pindex_t index)
-{
-	return (VM_RADIX_PCTRIE_REMOVE_LOOKUP(&rtree->rt_trie, index));
-}
-
-/*
- * Remove and free all the nodes from the radix tree.
- */
 static __inline void
-vm_radix_reclaim_allnodes(struct vm_radix *rtree)
+vm_radix_init(struct vm_radix *rtree)
 {
-	VM_RADIX_PCTRIE_RECLAIM(&rtree->rt_trie);
+	rtree->rt_root = VM_RADIX_NULL;
 }
 
-/*
- * Replace an existing page in the trie with another one.
- * Panics if there is not an old page in the trie at the new page's index.
- */
-static __inline vm_page_t
-vm_radix_replace(struct vm_radix *rtree, vm_page_t newpage)
+static __inline bool
+vm_radix_is_empty(struct vm_radix *rtree)
 {
-	return (VM_RADIX_PCTRIE_REPLACE(&rtree->rt_trie, newpage));
+	return (rtree->rt_root == VM_RADIX_NULL);
 }
 
 #endif /* _KERNEL */