sched/numa: Skip some page migrations after a shared fault
Shared faults can lead to lots of unnecessary page migrations,
slowing down the system, and causing private faults to hit the
per-pgdat migration ratelimit.
This patch adds sysctl numa_balancing_migrate_deferred, which specifies
how many shared page migrations to skip unconditionally, after each page
migration that is skipped because it is a shared fault.
This reduces the number of page migrations back and forth in
shared fault situations. It also gives a strong preference to
the tasks that are already running where most of the memory is,
and to moving the other tasks to near the memory.
Testing this with a much higher scan rate than the default
still seems to result in fewer page migrations than before.
Memory seems to be somewhat better consolidated than previously,
with multi-instance specjbb runs on a 4 node system.
Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1381141781-10992-62-git-send-email-mgorman@suse.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 2929c24..71cb253 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2301,6 +2301,35 @@
kmem_cache_free(sn_cache, n);
}
+#ifdef CONFIG_NUMA_BALANCING
+static bool numa_migrate_deferred(struct task_struct *p, int last_cpupid)
+{
+ /* Never defer a private fault */
+ if (cpupid_match_pid(p, last_cpupid))
+ return false;
+
+ if (p->numa_migrate_deferred) {
+ p->numa_migrate_deferred--;
+ return true;
+ }
+ return false;
+}
+
+static inline void defer_numa_migrate(struct task_struct *p)
+{
+ p->numa_migrate_deferred = sysctl_numa_balancing_migrate_deferred;
+}
+#else
+static inline bool numa_migrate_deferred(struct task_struct *p, int last_cpupid)
+{
+ return false;
+}
+
+static inline void defer_numa_migrate(struct task_struct *p)
+{
+}
+#endif /* CONFIG_NUMA_BALANCING */
+
/**
* mpol_misplaced - check whether current page node is valid in policy
*
@@ -2402,7 +2431,24 @@
* relation.
*/
last_cpupid = page_cpupid_xchg_last(page, this_cpupid);
- if (!cpupid_pid_unset(last_cpupid) && cpupid_to_nid(last_cpupid) != thisnid)
+ if (!cpupid_pid_unset(last_cpupid) && cpupid_to_nid(last_cpupid) != thisnid) {
+
+ /* See sysctl_numa_balancing_migrate_deferred comment */
+ if (!cpupid_match_pid(current, last_cpupid))
+ defer_numa_migrate(current);
+
+ goto out;
+ }
+
+ /*
+ * The quadratic filter above reduces extraneous migration
+ * of shared pages somewhat. This code reduces it even more,
+ * reducing the overhead of page migrations of shared pages.
+ * This makes workloads with shared pages rely more on
+ * "move task near its memory", and less on "move memory
+ * towards its task", which is exactly what we want.
+ */
+ if (numa_migrate_deferred(current, last_cpupid))
goto out;
}