vmscan: factor out kswapd sleeping logic from kswapd()

Currently, kswapd() has deep nesting and is slightly hard to read.  Clean
this up.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 46 insertions, 46 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 86f8c3418795..cacdf6684971 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2371,6 +2371,50 @@ out:
         return sc.nr_reclaimed;
 }
 
+static void kswapd_try_to_sleep(pg_data_t *pgdat, int order)
+{
+        long remaining = 0;
+        DEFINE_WAIT(wait);
+
+        if (freezing(current) || kthread_should_stop())
+                return;
+
+        prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
+
+        /* Try to sleep for a short interval */
+        if (!sleeping_prematurely(pgdat, 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(pgdat, order, remaining)) {
+                trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
+
+                /*
+                 * vmstat counters are not perfectly accurate and the estimated
+                 * value for counters such as NR_FREE_PAGES can deviate from the
+                 * true value by nr_online_cpus * threshold. To avoid the zone
+                 * watermarks being breached while under pressure, we reduce the
+                 * per-cpu vmstat threshold while kswapd is awake and restore
+                 * them before going back to sleep.
+                 */
+                set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
+                schedule();
+                set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
+        } else {
+                if (remaining)
+                        count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
+                else
+                        count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
+        }
+        finish_wait(&pgdat->kswapd_wait, &wait);
+}
+
 /*
  * The background pageout daemon, started as a kernel thread
  * from the init process.
@@ -2389,7 +2433,7 @@ static int kswapd(void *p)
         unsigned long order;
         pg_data_t *pgdat = (pg_data_t*)p;
         struct task_struct *tsk = current;
-        DEFINE_WAIT(wait);
+
         struct reclaim_state reclaim_state = {
                 .reclaimed_slab = 0,
         };
@@ -2421,7 +2465,6 @@ static int kswapd(void *p)
                 unsigned long new_order;
                 int ret;
 
-                prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
                 new_order = pgdat->kswapd_max_order;
                 pgdat->kswapd_max_order = 0;
                 if (order < new_order) {
@@ -2431,52 +2474,9 @@ static int kswapd(void *p)
                          */
                         order = new_order;
                 } else {
-                        if (!freezing(current) && !kthread_should_stop()) {
-                                long remaining = 0;
-
-                                /* Try to sleep for a short interval */
-                                if (!sleeping_prematurely(pgdat, 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(pgdat, order, remaining)) {
-                                        trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
-
-                                        /*
-                                         * vmstat counters are not perfectly
-                                         * accurate and the estimated value
-                                         * for counters such as NR_FREE_PAGES
-                                         * can deviate from the true value by
-                                         * nr_online_cpus * threshold. To
-                                         * avoid the zone watermarks being
-                                         * breached while under pressure, we
-                                         * reduce the per-cpu vmstat threshold
-                                         * while kswapd is awake and restore
-                                         * them before going back to sleep.
-                                         */
-                                        set_pgdat_percpu_threshold(pgdat,
-                                                calculate_normal_threshold);
-                                        schedule();
-                                        set_pgdat_percpu_threshold(pgdat,
-                                                calculate_pressure_threshold);
-                                } else {
-                                        if (remaining)
-                                                count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
-                                        else
-                                                count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
-                                }
-                        }
-
+                        kswapd_try_to_sleep(pgdat, order);
                         order = pgdat->kswapd_max_order;
                 }
-                finish_wait(&pgdat->kswapd_wait, &wait);
 
                 ret = try_to_freeze();
                 if (kthread_should_stop())