vmscan: have kswapd sleep for a short interval and double check it should be asleep

[firefly-linux-kernel-4.4.55.git] / mm / vmscan.c

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 61d3a9a0d96f87ec0ff29fdb68908ca13a810e7b..e176bd3936dad2a353e1747de62d128e79f0587b 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1904,6 +1904,24 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
 }
 #endif
 
+/* is kswapd sleeping prematurely? */
+static int sleeping_prematurely(int order, long remaining)
+{
+       struct zone *zone;
+
+       /* If a direct reclaimer woke kswapd within HZ/10, it's premature */
+       if (remaining)
+               return 1;
+
+       /* If after HZ/10, a zone is below the high mark, it's premature */
+       for_each_populated_zone(zone)
+               if (!zone_watermark_ok(zone, order, high_wmark_pages(zone),
+                                                               0, 0))
+                       return 1;
+
+       return 0;
+}
+
 /*
  * For kswapd, balance_pgdat() will work across all this node's zones until
  * they are all at high_wmark_pages(zone).
@@ -2185,8 +2203,30 @@ static int kswapd(void *p)
                         */
                        order = new_order;
                } else {
-                       if (!freezing(current) && !kthread_should_stop())
-                               schedule();
+                       if (!freezing(current) && !kthread_should_stop()) {
+                               long remaining = 0;
+
+                               /* Try to sleep for a short interval */
+                               if (!sleeping_prematurely(order, remaining)) {
+                                       remaining = schedule_timeout(HZ/10);
+                                       finish_wait(&pgdat->kswapd_wait, &wait);
+                                       prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
+                               }
+
+                               /*
+                                * After a short sleep, check if it was a
+                                * premature sleep. If not, then go fully
+                                * to sleep until explicitly woken up
+                                */
+                               if (!sleeping_prematurely(order, remaining))
+                                       schedule();
+                               else {
+                                       if (remaining)
+                                               count_vm_event(KSWAPD_PREMATURE_FAST);
+                                       else
+                                               count_vm_event(KSWAPD_PREMATURE_SLOW);
+                               }
+                       }
 
                        order = pgdat->kswapd_max_order;
                }