1 files changed, 29 insertions, 1 deletions

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 4c1c8d83ac6a..fd20e28fd2ad 100644
--- a/mm/mempolicy.c
+++ b/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: