---

yaml
---
r: 344810
b: refs/heads/master
c: e42c8ff
h: refs/heads/master
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: bac0382c6ad764156025978845147e5a6eccca09
+refs/heads/master: e42c8ff2999de1239a57d434bfbd8e9f2a56e814

trunk/mm/mempolicy.c

@@ -2317,9 +2317,37 @@ int mpol_misplaced(struct page *page, struct vm_area_struct *vma, unsigned long
 	}
 
 	/* Migrate the page towards the node whose CPU is referencing it */
-	if (pol->flags & MPOL_F_MORON)
+	if (pol->flags & MPOL_F_MORON) {
+		int last_nid;
+
 		polnid = numa_node_id();
 
+		/*
+		 * Multi-stage node selection is used in conjunction
+		 * with a periodic migration fault to build a temporal
+		 * task<->page relation. By using a two-stage filter we
+		 * remove short/unlikely relations.
+		 *
+		 * Using P(p) ~ n_p / n_t as per frequentist
+		 * probability, we can equate a task's usage of a
+		 * particular page (n_p) per total usage of this
+		 * page (n_t) (in a given time-span) to a probability.
+		 *
+		 * Our periodic faults will sample this probability and
+		 * getting the same result twice in a row, given these
+		 * samples are fully independent, is then given by
+		 * P(n)^2, provided our sample period is sufficiently
+		 * short compared to the usage pattern.
+		 *
+		 * This quadric squishes small probabilities, making
+		 * it less likely we act on an unlikely task<->page
+		 * relation.
+		 */
+		last_nid = page_xchg_last_nid(page, polnid);
+		if (last_nid != polnid)
+			goto out;
+	}
+
 	if (curnid != polnid)
 		ret = polnid;
 out: