sched/numa, mm: Use active_nodes nodemask to limit numa migrations

Use the active_nodes nodemask to make smarter decisions on NUMA migrations.

In order to maximize performance of workloads that do not fit in one NUMA
node, we want to satisfy the following criteria:

  1) keep private memory local to each thread

  2) avoid excessive NUMA migration of pages

  3) distribute shared memory across the active nodes, to
     maximize memory bandwidth available to the workload

This patch accomplishes that by implementing the following policy for
NUMA migrations:

  1) always migrate on a private fault

  2) never migrate to a node that is not in the set of active nodes
     for the numa_group

  3) always migrate from a node outside of the set of active nodes,
     to a node that is in that set

  4) within the set of active nodes in the numa_group, only migrate
     from a node with more NUMA page faults, to a node with fewer
     NUMA page faults, with a 25% margin to avoid ping-ponging

This results in most pages of a workload ending up on the actively
used nodes, with reduced ping-ponging of pages between those nodes.

Signed-off-by: Rik van Riel <riel@redhat.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Chegu Vinod <chegu_vinod@hp.com>
Link: http://lkml.kernel.org/r/1390860228-21539-6-git-send-email-riel@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 1 insertions, 28 deletions

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 68d5c7f..784c11e 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2377,37 +2377,10 @@ 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) {
-		int last_cpupid;
-		int this_cpupid;
-
 		polnid = thisnid;
-		this_cpupid = cpu_pid_to_cpupid(thiscpu, current->pid);
 
-		/*
-		 * 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_cpupid = page_cpupid_xchg_last(page, this_cpupid);
-		if (!cpupid_pid_unset(last_cpupid) && cpupid_to_nid(last_cpupid) != thisnid) {
+		if (!should_numa_migrate_memory(current, page, curnid, thiscpu))
 			goto out;
-		}
 	}
 
 	if (curnid != polnid)