diff --git a/mm/prio_tree.c b/mm/prio_tree.c
new file mode 100644
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+++ b/mm/prio_tree.c
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+/*
+ * mm/prio_tree.c - priority search tree for mapping->i_mmap
+ *
+ * Copyright (C) 2004, Rajesh Venkatasubramanian <vrajesh@umich.edu>
+ *
+ * This file is released under the GPL v2.
+ *
+ * Based on the radix priority search tree proposed by Edward M. McCreight
+ * SIAM Journal of Computing, vol. 14, no.2, pages 257-276, May 1985
+ *
+ * 02Feb2004	Initial version
+ */
+
+#include <linux/mm.h>
+#include <linux/prio_tree.h>
+
+/*
+ * See lib/prio_tree.c for details on the general radix priority search tree
+ * code.
+ */
+
+/*
+ * The following #defines are mirrored from lib/prio_tree.c. They're only used
+ * for debugging, and should be removed (along with the debugging code using
+ * them) when switching also VMAs to the regular prio_tree code.
+ */
+
+#define RADIX_INDEX(vma)  ((vma)->vm_pgoff)
+#define VMA_SIZE(vma)	  (((vma)->vm_end - (vma)->vm_start) >> PAGE_SHIFT)
+/* avoid overflow */
+#define HEAP_INDEX(vma)   ((vma)->vm_pgoff + (VMA_SIZE(vma) - 1))
+
+/*
+ * Radix priority search tree for address_space->i_mmap
+ *
+ * For each vma that map a unique set of file pages i.e., unique [radix_index,
+ * heap_index] value, we have a corresponing priority search tree node. If
+ * multiple vmas have identical [radix_index, heap_index] value, then one of
+ * them is used as a tree node and others are stored in a vm_set list. The tree
+ * node points to the first vma (head) of the list using vm_set.head.
+ *
+ * prio_tree_root
+ *      |
+ *      A       vm_set.head
+ *     / \      /
+ *    L   R -> H-I-J-K-M-N-O-P-Q-S
+ *    ^   ^    <-- vm_set.list -->
+ *  tree nodes
+ *
+ * We need some way to identify whether a vma is a tree node, head of a vm_set
+ * list, or just a member of a vm_set list. We cannot use vm_flags to store
+ * such information. The reason is, in the above figure, it is possible that
+ * vm_flags' of R and H are covered by the different mmap_sems. When R is
+ * removed under R->mmap_sem, H replaces R as a tree node. Since we do not hold
+ * H->mmap_sem, we cannot use H->vm_flags for marking that H is a tree node now.
+ * That's why some trick involving shared.vm_set.parent is used for identifying
+ * tree nodes and list head nodes.
+ *
+ * vma radix priority search tree node rules:
+ *
+ * vma->shared.vm_set.parent != NULL    ==> a tree node
+ *      vma->shared.vm_set.head != NULL ==> list of others mapping same range
+ *      vma->shared.vm_set.head == NULL ==> no others map the same range
+ *
+ * vma->shared.vm_set.parent == NULL
+ * 	vma->shared.vm_set.head != NULL ==> list head of vmas mapping same range
+ * 	vma->shared.vm_set.head == NULL ==> a list node
+ */
+
+/*
+ * Add a new vma known to map the same set of pages as the old vma:
+ * useful for fork's dup_mmap as well as vma_prio_tree_insert below.
+ * Note that it just happens to work correctly on i_mmap_nonlinear too.
+ */
+void vma_prio_tree_add(struct vm_area_struct *vma, struct vm_area_struct *old)
+{
+	/* Leave these BUG_ONs till prio_tree patch stabilizes */
+	BUG_ON(RADIX_INDEX(vma) != RADIX_INDEX(old));
+	BUG_ON(HEAP_INDEX(vma) != HEAP_INDEX(old));
+
+	vma->shared.vm_set.head = NULL;
+	vma->shared.vm_set.parent = NULL;
+
+	if (!old->shared.vm_set.parent)
+		list_add(&vma->shared.vm_set.list,
+				&old->shared.vm_set.list);
+	else if (old->shared.vm_set.head)
+		list_add_tail(&vma->shared.vm_set.list,
+				&old->shared.vm_set.head->shared.vm_set.list);
+	else {
+		INIT_LIST_HEAD(&vma->shared.vm_set.list);
+		vma->shared.vm_set.head = old;
+		old->shared.vm_set.head = vma;
+	}
+}
+
+void vma_prio_tree_insert(struct vm_area_struct *vma,
+			  struct prio_tree_root *root)
+{
+	struct prio_tree_node *ptr;
+	struct vm_area_struct *old;
+
+	vma->shared.vm_set.head = NULL;
+
+	ptr = raw_prio_tree_insert(root, &vma->shared.prio_tree_node);
+	if (ptr != (struct prio_tree_node *) &vma->shared.prio_tree_node) {
+		old = prio_tree_entry(ptr, struct vm_area_struct,
+					shared.prio_tree_node);
+		vma_prio_tree_add(vma, old);
+	}
+}
+
+void vma_prio_tree_remove(struct vm_area_struct *vma,
+			  struct prio_tree_root *root)
+{
+	struct vm_area_struct *node, *head, *new_head;
+
+	if (!vma->shared.vm_set.head) {
+		if (!vma->shared.vm_set.parent)
+			list_del_init(&vma->shared.vm_set.list);
+		else
+			raw_prio_tree_remove(root, &vma->shared.prio_tree_node);
+	} else {
+		/* Leave this BUG_ON till prio_tree patch stabilizes */
+		BUG_ON(vma->shared.vm_set.head->shared.vm_set.head != vma);
+		if (vma->shared.vm_set.parent) {
+			head = vma->shared.vm_set.head;
+			if (!list_empty(&head->shared.vm_set.list)) {
+				new_head = list_entry(
+					head->shared.vm_set.list.next,
+					struct vm_area_struct,
+					shared.vm_set.list);
+				list_del_init(&head->shared.vm_set.list);
+			} else
+				new_head = NULL;
+
+			raw_prio_tree_replace(root, &vma->shared.prio_tree_node,
+					&head->shared.prio_tree_node);
+			head->shared.vm_set.head = new_head;
+			if (new_head)
+				new_head->shared.vm_set.head = head;
+
+		} else {
+			node = vma->shared.vm_set.head;
+			if (!list_empty(&vma->shared.vm_set.list)) {
+				new_head = list_entry(
+					vma->shared.vm_set.list.next,
+					struct vm_area_struct,
+					shared.vm_set.list);
+				list_del_init(&vma->shared.vm_set.list);
+				node->shared.vm_set.head = new_head;
+				new_head->shared.vm_set.head = node;
+			} else
+				node->shared.vm_set.head = NULL;
+		}
+	}
+}
+
+/*
+ * Helper function to enumerate vmas that map a given file page or a set of
+ * contiguous file pages. The function returns vmas that at least map a single
+ * page in the given range of contiguous file pages.
+ */
+struct vm_area_struct *vma_prio_tree_next(struct vm_area_struct *vma,
+					struct prio_tree_iter *iter)
+{
+	struct prio_tree_node *ptr;
+	struct vm_area_struct *next;
+
+	if (!vma) {
+		/*
+		 * First call is with NULL vma
+		 */
+		ptr = prio_tree_next(iter);
+		if (ptr) {
+			next = prio_tree_entry(ptr, struct vm_area_struct,
+						shared.prio_tree_node);
+			prefetch(next->shared.vm_set.head);
+			return next;
+		} else
+			return NULL;
+	}
+
+	if (vma->shared.vm_set.parent) {
+		if (vma->shared.vm_set.head) {
+			next = vma->shared.vm_set.head;
+			prefetch(next->shared.vm_set.list.next);
+			return next;
+		}
+	} else {
+		next = list_entry(vma->shared.vm_set.list.next,
+				struct vm_area_struct, shared.vm_set.list);
+		if (!next->shared.vm_set.head) {
+			prefetch(next->shared.vm_set.list.next);
+			return next;
+		}
+	}
+
+	ptr = prio_tree_next(iter);
+	if (ptr) {
+		next = prio_tree_entry(ptr, struct vm_area_struct,
+					shared.prio_tree_node);
+		prefetch(next->shared.vm_set.head);
+		return next;
+	} else
+		return NULL;
+}