diff --git a/mm/ksm.c b/mm/ksm.c
index d3842b2..1602cc9 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -36,6 +36,7 @@
 #include <linux/hashtable.h>
 #include <linux/freezer.h>
 #include <linux/oom.h>
+#include <linux/numa.h>
 
 #include <asm/tlbflush.h>
 #include "internal.h"
@@ -139,6 +140,9 @@
 	struct mm_struct *mm;
 	unsigned long address;		/* + low bits used for flags below */
 	unsigned int oldchecksum;	/* when unstable */
+#ifdef CONFIG_NUMA
+	unsigned int nid;
+#endif
 	union {
 		struct rb_node node;	/* when node of unstable tree */
 		struct {		/* when listed from stable tree */
@@ -153,8 +157,8 @@
 #define STABLE_FLAG	0x200	/* is listed from the stable tree */
 
 /* The stable and unstable tree heads */
-static struct rb_root root_stable_tree = RB_ROOT;
-static struct rb_root root_unstable_tree = RB_ROOT;
+static struct rb_root root_unstable_tree[MAX_NUMNODES];
+static struct rb_root root_stable_tree[MAX_NUMNODES];
 
 #define MM_SLOTS_HASH_BITS 10
 static DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
@@ -188,6 +192,9 @@
 /* Milliseconds ksmd should sleep between batches */
 static unsigned int ksm_thread_sleep_millisecs = 20;
 
+/* Zeroed when merging across nodes is not allowed */
+static unsigned int ksm_merge_across_nodes = 1;
+
 #define KSM_RUN_STOP	0
 #define KSM_RUN_MERGE	1
 #define KSM_RUN_UNMERGE	2
@@ -441,10 +448,25 @@
 	return page;
 }
 
+/*
+ * This helper is used for getting right index into array of tree roots.
+ * When merge_across_nodes knob is set to 1, there are only two rb-trees for
+ * stable and unstable pages from all nodes with roots in index 0. Otherwise,
+ * every node has its own stable and unstable tree.
+ */
+static inline int get_kpfn_nid(unsigned long kpfn)
+{
+	if (ksm_merge_across_nodes)
+		return 0;
+	else
+		return pfn_to_nid(kpfn);
+}
+
 static void remove_node_from_stable_tree(struct stable_node *stable_node)
 {
 	struct rmap_item *rmap_item;
 	struct hlist_node *hlist;
+	int nid;
 
 	hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
 		if (rmap_item->hlist.next)
@@ -456,7 +478,9 @@
 		cond_resched();
 	}
 
-	rb_erase(&stable_node->node, &root_stable_tree);
+	nid = get_kpfn_nid(stable_node->kpfn);
+
+	rb_erase(&stable_node->node, &root_stable_tree[nid]);
 	free_stable_node(stable_node);
 }
 
@@ -554,7 +578,12 @@
 		age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
 		BUG_ON(age > 1);
 		if (!age)
-			rb_erase(&rmap_item->node, &root_unstable_tree);
+#ifdef CONFIG_NUMA
+			rb_erase(&rmap_item->node,
+					&root_unstable_tree[rmap_item->nid]);
+#else
+			rb_erase(&rmap_item->node, &root_unstable_tree[0]);
+#endif
 
 		ksm_pages_unshared--;
 		rmap_item->address &= PAGE_MASK;
@@ -990,8 +1019,9 @@
  */
 static struct page *stable_tree_search(struct page *page)
 {
-	struct rb_node *node = root_stable_tree.rb_node;
+	struct rb_node *node;
 	struct stable_node *stable_node;
+	int nid;
 
 	stable_node = page_stable_node(page);
 	if (stable_node) {			/* ksm page forked */
@@ -999,6 +1029,9 @@
 		return page;
 	}
 
+	nid = get_kpfn_nid(page_to_pfn(page));
+	node = root_stable_tree[nid].rb_node;
+
 	while (node) {
 		struct page *tree_page;
 		int ret;
@@ -1033,10 +1066,16 @@
  */
 static struct stable_node *stable_tree_insert(struct page *kpage)
 {
-	struct rb_node **new = &root_stable_tree.rb_node;
+	int nid;
+	unsigned long kpfn;
+	struct rb_node **new;
 	struct rb_node *parent = NULL;
 	struct stable_node *stable_node;
 
+	kpfn = page_to_pfn(kpage);
+	nid = get_kpfn_nid(kpfn);
+	new = &root_stable_tree[nid].rb_node;
+
 	while (*new) {
 		struct page *tree_page;
 		int ret;
@@ -1070,11 +1109,11 @@
 		return NULL;
 
 	rb_link_node(&stable_node->node, parent, new);
-	rb_insert_color(&stable_node->node, &root_stable_tree);
+	rb_insert_color(&stable_node->node, &root_stable_tree[nid]);
 
 	INIT_HLIST_HEAD(&stable_node->hlist);
 
-	stable_node->kpfn = page_to_pfn(kpage);
+	stable_node->kpfn = kpfn;
 	set_page_stable_node(kpage, stable_node);
 
 	return stable_node;
@@ -1098,10 +1137,15 @@
 struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
 					      struct page *page,
 					      struct page **tree_pagep)
-
 {
-	struct rb_node **new = &root_unstable_tree.rb_node;
+	struct rb_node **new;
+	struct rb_root *root;
 	struct rb_node *parent = NULL;
+	int nid;
+
+	nid = get_kpfn_nid(page_to_pfn(page));
+	root = &root_unstable_tree[nid];
+	new = &root->rb_node;
 
 	while (*new) {
 		struct rmap_item *tree_rmap_item;
@@ -1122,6 +1166,18 @@
 			return NULL;
 		}
 
+		/*
+		 * If tree_page has been migrated to another NUMA node, it
+		 * will be flushed out and put into the right unstable tree
+		 * next time: only merge with it if merge_across_nodes.
+		 * Just notice, we don't have similar problem for PageKsm
+		 * because their migration is disabled now. (62b61f611e)
+		 */
+		if (!ksm_merge_across_nodes && page_to_nid(tree_page) != nid) {
+			put_page(tree_page);
+			return NULL;
+		}
+
 		ret = memcmp_pages(page, tree_page);
 
 		parent = *new;
@@ -1139,8 +1195,11 @@
 
 	rmap_item->address |= UNSTABLE_FLAG;
 	rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
+#ifdef CONFIG_NUMA
+	rmap_item->nid = nid;
+#endif
 	rb_link_node(&rmap_item->node, parent, new);
-	rb_insert_color(&rmap_item->node, &root_unstable_tree);
+	rb_insert_color(&rmap_item->node, root);
 
 	ksm_pages_unshared++;
 	return NULL;
@@ -1154,6 +1213,13 @@
 static void stable_tree_append(struct rmap_item *rmap_item,
 			       struct stable_node *stable_node)
 {
+#ifdef CONFIG_NUMA
+	/*
+	 * Usually rmap_item->nid is already set correctly,
+	 * but it may be wrong after switching merge_across_nodes.
+	 */
+	rmap_item->nid = get_kpfn_nid(stable_node->kpfn);
+#endif
 	rmap_item->head = stable_node;
 	rmap_item->address |= STABLE_FLAG;
 	hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
@@ -1283,6 +1349,7 @@
 	struct mm_slot *slot;
 	struct vm_area_struct *vma;
 	struct rmap_item *rmap_item;
+	int nid;
 
 	if (list_empty(&ksm_mm_head.mm_list))
 		return NULL;
@@ -1301,7 +1368,8 @@
 		 */
 		lru_add_drain_all();
 
-		root_unstable_tree = RB_ROOT;
+		for (nid = 0; nid < nr_node_ids; nid++)
+			root_unstable_tree[nid] = RB_ROOT;
 
 		spin_lock(&ksm_mmlist_lock);
 		slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
@@ -1770,15 +1838,19 @@
 						 unsigned long end_pfn)
 {
 	struct rb_node *node;
+	int nid;
 
-	for (node = rb_first(&root_stable_tree); node; node = rb_next(node)) {
-		struct stable_node *stable_node;
+	for (nid = 0; nid < nr_node_ids; nid++)
+		for (node = rb_first(&root_stable_tree[nid]); node;
+				node = rb_next(node)) {
+			struct stable_node *stable_node;
 
-		stable_node = rb_entry(node, struct stable_node, node);
-		if (stable_node->kpfn >= start_pfn &&
-		    stable_node->kpfn < end_pfn)
-			return stable_node;
-	}
+			stable_node = rb_entry(node, struct stable_node, node);
+			if (stable_node->kpfn >= start_pfn &&
+			    stable_node->kpfn < end_pfn)
+				return stable_node;
+		}
+
 	return NULL;
 }
 
@@ -1925,6 +1997,40 @@
 }
 KSM_ATTR(run);
 
+#ifdef CONFIG_NUMA
+static ssize_t merge_across_nodes_show(struct kobject *kobj,
+				struct kobj_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%u\n", ksm_merge_across_nodes);
+}
+
+static ssize_t merge_across_nodes_store(struct kobject *kobj,
+				   struct kobj_attribute *attr,
+				   const char *buf, size_t count)
+{
+	int err;
+	unsigned long knob;
+
+	err = kstrtoul(buf, 10, &knob);
+	if (err)
+		return err;
+	if (knob > 1)
+		return -EINVAL;
+
+	mutex_lock(&ksm_thread_mutex);
+	if (ksm_merge_across_nodes != knob) {
+		if (ksm_pages_shared)
+			err = -EBUSY;
+		else
+			ksm_merge_across_nodes = knob;
+	}
+	mutex_unlock(&ksm_thread_mutex);
+
+	return err ? err : count;
+}
+KSM_ATTR(merge_across_nodes);
+#endif
+
 static ssize_t pages_shared_show(struct kobject *kobj,
 				 struct kobj_attribute *attr, char *buf)
 {
@@ -1979,6 +2085,9 @@
 	&pages_unshared_attr.attr,
 	&pages_volatile_attr.attr,
 	&full_scans_attr.attr,
+#ifdef CONFIG_NUMA
+	&merge_across_nodes_attr.attr,
+#endif
 	NULL,
 };
 
@@ -1992,11 +2101,15 @@
 {
 	struct task_struct *ksm_thread;
 	int err;
+	int nid;
 
 	err = ksm_slab_init();
 	if (err)
 		goto out;
 
+	for (nid = 0; nid < nr_node_ids; nid++)
+		root_stable_tree[nid] = RB_ROOT;
+
 	ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
 	if (IS_ERR(ksm_thread)) {
 		printk(KERN_ERR "ksm: creating kthread failed\n");