mm: numa: Migrate on reference policy

This is the simplest possible policy that still does something of note.
When a pte_numa is faulted, it is moved immediately. Any replacement
policy must at least do better than this and in all likelihood this
policy regresses normal workloads.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Acked-by: Rik van Riel <riel@redhat.com>

1 files changed, 36 insertions, 2 deletions

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 516491fbfaa8..4c1c8d83ac6a 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -118,6 +118,26 @@ static struct mempolicy default_policy = {
         .flags = MPOL_F_LOCAL,
 };
 
+static struct mempolicy preferred_node_policy[MAX_NUMNODES];
+
+static struct mempolicy *get_task_policy(struct task_struct *p)
+{
+        struct mempolicy *pol = p->mempolicy;
+        int node;
+
+        if (!pol) {
+                node = numa_node_id();
+                if (node != -1)
+                        pol = &preferred_node_policy[node];
+
+                /* preferred_node_policy is not initialised early in boot */
+                if (!pol->mode)
+                        pol = NULL;
+        }
+
+        return pol;
+}
+
 static const struct mempolicy_operations {
         int (*create)(struct mempolicy *pol, const nodemask_t *nodes);
         /*
@@ -1598,7 +1618,7 @@ asmlinkage long compat_sys_mbind(compat_ulong_t start, compat_ulong_t len,
 struct mempolicy *get_vma_policy(struct task_struct *task,
                 struct vm_area_struct *vma, unsigned long addr)
 {
-        struct mempolicy *pol = task->mempolicy;
+        struct mempolicy *pol = get_task_policy(task);
 
         if (vma) {
                 if (vma->vm_ops && vma->vm_ops->get_policy) {
@@ -2021,7 +2041,7 @@ retry_cpuset:
  */
 struct page *alloc_pages_current(gfp_t gfp, unsigned order)
 {
-        struct mempolicy *pol = current->mempolicy;
+        struct mempolicy *pol = get_task_policy(current);
         struct page *page;
         unsigned int cpuset_mems_cookie;
 
@@ -2295,6 +2315,11 @@ int mpol_misplaced(struct page *page, struct vm_area_struct *vma, unsigned long
         default:
                 BUG();
         }
+
+        /* Migrate the page towards the node whose CPU is referencing it */
+        if (pol->flags & MPOL_F_MORON)
+                polnid = numa_node_id();
+
         if (curnid != polnid)
                 ret = polnid;
 out:
@@ -2483,6 +2508,15 @@ void __init numa_policy_init(void)
                                      sizeof(struct sp_node),
                                      0, SLAB_PANIC, NULL);
 
+        for_each_node(nid) {
+                preferred_node_policy[nid] = (struct mempolicy) {
+                        .refcnt = ATOMIC_INIT(1),
+                        .mode = MPOL_PREFERRED,
+                        .flags = MPOL_F_MOF | MPOL_F_MORON,
+                        .v = { .preferred_node = nid, },
+                };
+        }
+
         /*
          * Set interleaving policy for system init. Interleaving is only
          * enabled across suitably sized nodes (default is >= 16MB), or