diff --git a/include/linux/mm.h b/include/linux/mm.h
index ce464cd..81443d5 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -691,6 +691,12 @@
 	return cpupid_to_cpu(cpupid) == (-1 & LAST__CPU_MASK);
 }
 
+static inline bool __cpupid_match_pid(pid_t task_pid, int cpupid)
+{
+	return (task_pid & LAST__PID_MASK) == cpupid_to_pid(cpupid);
+}
+
+#define cpupid_match_pid(task, cpupid) __cpupid_match_pid(task->pid, cpupid)
 #ifdef LAST_CPUPID_NOT_IN_PAGE_FLAGS
 static inline int page_cpupid_xchg_last(struct page *page, int cpupid)
 {
@@ -760,6 +766,11 @@
 static inline void page_cpupid_reset_last(struct page *page)
 {
 }
+
+static inline bool cpupid_match_pid(struct task_struct *task, int cpupid)
+{
+	return false;
+}
 #endif /* CONFIG_NUMA_BALANCING */
 
 static inline struct zone *page_zone(const struct page *page)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index b661979..f587ded 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1347,6 +1347,9 @@
 	u64 node_stamp;			/* migration stamp  */
 	struct callback_head numa_work;
 
+	struct list_head numa_entry;
+	struct numa_group *numa_group;
+
 	/*
 	 * Exponential decaying average of faults on a per-node basis.
 	 * Scheduling placement decisions are made based on the these counts.
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 1fe59da..51092d5 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1733,6 +1733,9 @@
 	p->numa_work.next = &p->numa_work;
 	p->numa_faults = NULL;
 	p->numa_faults_buffer = NULL;
+
+	INIT_LIST_HEAD(&p->numa_entry);
+	p->numa_group = NULL;
 #endif /* CONFIG_NUMA_BALANCING */
 }
 
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index dbe0f62..8556505 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -888,6 +888,17 @@
  */
 unsigned int sysctl_numa_balancing_settle_count __read_mostly = 4;
 
+struct numa_group {
+	atomic_t refcount;
+
+	spinlock_t lock; /* nr_tasks, tasks */
+	int nr_tasks;
+	struct list_head task_list;
+
+	struct rcu_head rcu;
+	atomic_long_t faults[0];
+};
+
 static inline int task_faults_idx(int nid, int priv)
 {
 	return 2 * nid + priv;
@@ -1182,7 +1193,10 @@
 		int priv, i;
 
 		for (priv = 0; priv < 2; priv++) {
+			long diff;
+
 			i = task_faults_idx(nid, priv);
+			diff = -p->numa_faults[i];
 
 			/* Decay existing window, copy faults since last scan */
 			p->numa_faults[i] >>= 1;
@@ -1190,6 +1204,11 @@
 			p->numa_faults_buffer[i] = 0;
 
 			faults += p->numa_faults[i];
+			diff += p->numa_faults[i];
+			if (p->numa_group) {
+				/* safe because we can only change our own group */
+				atomic_long_add(diff, &p->numa_group->faults[i]);
+			}
 		}
 
 		if (faults > max_faults) {
@@ -1207,6 +1226,131 @@
 	}
 }
 
+static inline int get_numa_group(struct numa_group *grp)
+{
+	return atomic_inc_not_zero(&grp->refcount);
+}
+
+static inline void put_numa_group(struct numa_group *grp)
+{
+	if (atomic_dec_and_test(&grp->refcount))
+		kfree_rcu(grp, rcu);
+}
+
+static void double_lock(spinlock_t *l1, spinlock_t *l2)
+{
+	if (l1 > l2)
+		swap(l1, l2);
+
+	spin_lock(l1);
+	spin_lock_nested(l2, SINGLE_DEPTH_NESTING);
+}
+
+static void task_numa_group(struct task_struct *p, int cpupid)
+{
+	struct numa_group *grp, *my_grp;
+	struct task_struct *tsk;
+	bool join = false;
+	int cpu = cpupid_to_cpu(cpupid);
+	int i;
+
+	if (unlikely(!p->numa_group)) {
+		unsigned int size = sizeof(struct numa_group) +
+				    2*nr_node_ids*sizeof(atomic_long_t);
+
+		grp = kzalloc(size, GFP_KERNEL | __GFP_NOWARN);
+		if (!grp)
+			return;
+
+		atomic_set(&grp->refcount, 1);
+		spin_lock_init(&grp->lock);
+		INIT_LIST_HEAD(&grp->task_list);
+
+		for (i = 0; i < 2*nr_node_ids; i++)
+			atomic_long_set(&grp->faults[i], p->numa_faults[i]);
+
+		list_add(&p->numa_entry, &grp->task_list);
+		grp->nr_tasks++;
+		rcu_assign_pointer(p->numa_group, grp);
+	}
+
+	rcu_read_lock();
+	tsk = ACCESS_ONCE(cpu_rq(cpu)->curr);
+
+	if (!cpupid_match_pid(tsk, cpupid))
+		goto unlock;
+
+	grp = rcu_dereference(tsk->numa_group);
+	if (!grp)
+		goto unlock;
+
+	my_grp = p->numa_group;
+	if (grp == my_grp)
+		goto unlock;
+
+	/*
+	 * Only join the other group if its bigger; if we're the bigger group,
+	 * the other task will join us.
+	 */
+	if (my_grp->nr_tasks > grp->nr_tasks)
+		goto unlock;
+
+	/*
+	 * Tie-break on the grp address.
+	 */
+	if (my_grp->nr_tasks == grp->nr_tasks && my_grp > grp)
+		goto unlock;
+
+	if (!get_numa_group(grp))
+		goto unlock;
+
+	join = true;
+
+unlock:
+	rcu_read_unlock();
+
+	if (!join)
+		return;
+
+	for (i = 0; i < 2*nr_node_ids; i++) {
+		atomic_long_sub(p->numa_faults[i], &my_grp->faults[i]);
+		atomic_long_add(p->numa_faults[i], &grp->faults[i]);
+	}
+
+	double_lock(&my_grp->lock, &grp->lock);
+
+	list_move(&p->numa_entry, &grp->task_list);
+	my_grp->nr_tasks--;
+	grp->nr_tasks++;
+
+	spin_unlock(&my_grp->lock);
+	spin_unlock(&grp->lock);
+
+	rcu_assign_pointer(p->numa_group, grp);
+
+	put_numa_group(my_grp);
+}
+
+void task_numa_free(struct task_struct *p)
+{
+	struct numa_group *grp = p->numa_group;
+	int i;
+
+	if (grp) {
+		for (i = 0; i < 2*nr_node_ids; i++)
+			atomic_long_sub(p->numa_faults[i], &grp->faults[i]);
+
+		spin_lock(&grp->lock);
+		list_del(&p->numa_entry);
+		grp->nr_tasks--;
+		spin_unlock(&grp->lock);
+		rcu_assign_pointer(p->numa_group, NULL);
+		put_numa_group(grp);
+	}
+
+	kfree(p->numa_faults);
+}
+
 /*
  * Got a PROT_NONE fault for a page on @node.
  */
@@ -1222,15 +1366,6 @@
 	if (!p->mm)
 		return;
 
-	/*
-	 * First accesses are treated as private, otherwise consider accesses
-	 * to be private if the accessing pid has not changed
-	 */
-	if (!cpupid_pid_unset(last_cpupid))
-		priv = ((p->pid & LAST__PID_MASK) == cpupid_to_pid(last_cpupid));
-	else
-		priv = 1;
-
 	/* Allocate buffer to track faults on a per-node basis */
 	if (unlikely(!p->numa_faults)) {
 		int size = sizeof(*p->numa_faults) * 2 * nr_node_ids;
@@ -1245,6 +1380,18 @@
 	}
 
 	/*
+	 * First accesses are treated as private, otherwise consider accesses
+	 * to be private if the accessing pid has not changed
+	 */
+	if (unlikely(last_cpupid == (-1 & LAST_CPUPID_MASK))) {
+		priv = 1;
+	} else {
+		priv = cpupid_match_pid(p, last_cpupid);
+		if (!priv)
+			task_numa_group(p, last_cpupid);
+	}
+
+	/*
 	 * If pages are properly placed (did not migrate) then scan slower.
 	 * This is reset periodically in case of phase changes
 	 */
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 691e969..8037b10 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -559,10 +559,7 @@
 #ifdef CONFIG_NUMA_BALANCING
 extern int migrate_task_to(struct task_struct *p, int cpu);
 extern int migrate_swap(struct task_struct *, struct task_struct *);
-static inline void task_numa_free(struct task_struct *p)
-{
-	kfree(p->numa_faults);
-}
+extern void task_numa_free(struct task_struct *p);
 #else /* CONFIG_NUMA_BALANCING */
 static inline void task_numa_free(struct task_struct *p)
 {
diff --git a/mm/memory.c b/mm/memory.c
index 5162e6d..c57efa2 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2719,6 +2719,14 @@
 		get_page(dirty_page);
 
 reuse:
+		/*
+		 * Clear the pages cpupid information as the existing
+		 * information potentially belongs to a now completely
+		 * unrelated process.
+		 */
+		if (old_page)
+			page_cpupid_xchg_last(old_page, (1 << LAST_CPUPID_SHIFT) - 1);
+
 		flush_cache_page(vma, address, pte_pfn(orig_pte));
 		entry = pte_mkyoung(orig_pte);
 		entry = maybe_mkwrite(pte_mkdirty(entry), vma);