sched/numa: Slow scan rate if no NUMA hinting faults are being recorded

NUMA PTE scanning slows if a NUMA hinting fault was trapped and no page
was migrated. For long-lived but idle processes there may be no faults
but the scan rate will be high and just waste CPU. This patch will slow
the scan rate for processes that are not trapping faults.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Rik van Riel <riel@redhat.com>
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/1381141781-10992-19-git-send-email-mgorman@suse.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e08d757720dec4a5615739f71e45421008f2de94..c6c330245f7ff0bfdcddfdc8ff8c0ddee686e40a 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1038,6 +1038,18 @@ void task_numa_work(struct callback_head *work)
        }
 
 out:
+       /*
+        * If the whole process was scanned without updates then no NUMA
+        * hinting faults are being recorded and scan rate should be lower.
+        */
+       if (mm->numa_scan_offset == 0 && !nr_pte_updates) {
+               p->numa_scan_period = min(p->numa_scan_period_max,
+                       p->numa_scan_period << 1);
+
+               next_scan = now + msecs_to_jiffies(p->numa_scan_period);
+               mm->numa_next_scan = next_scan;
+       }
+
        /*
         * It is possible to reach the end of the VMA list but the last few
         * VMAs are not guaranteed to the vma_migratable. If they are not, we