On Thu, Feb 16, 2017 at 02:23:08PM +0800, Hillf Danton wrote:

On February 15, 2017 5:23 PM Mel Gorman wrote: 

quoted

  */
 static int kswapd(void *p)
 {
-	unsigned int alloc_order, reclaim_order, classzone_idx;
+	unsigned int alloc_order, reclaim_order;
+	unsigned int classzone_idx = MAX_NR_ZONES - 1;
 	pg_data_t *pgdat = (pg_data_t*)p;
 	struct task_struct *tsk = current;

@@ -3447,20 +3466,23 @@ static int kswapd(void *p)
 	tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
 	set_freezable();

-	pgdat->kswapd_order = alloc_order = reclaim_order = 0;
-	pgdat->kswapd_classzone_idx = classzone_idx = 0;
+	pgdat->kswapd_order = 0;
+	pgdat->kswapd_classzone_idx = MAX_NR_ZONES;
 	for ( ; ; ) {
 		bool ret;

+		alloc_order = reclaim_order = pgdat->kswapd_order;
+		classzone_idx = kswapd_classzone_idx(pgdat, classzone_idx);
+
 kswapd_try_sleep:
 		kswapd_try_to_sleep(pgdat, alloc_order, reclaim_order,
 					classzone_idx);

 		/* Read the new order and classzone_idx */
 		alloc_order = reclaim_order = pgdat->kswapd_order;
-		classzone_idx = pgdat->kswapd_classzone_idx;
+		classzone_idx = kswapd_classzone_idx(pgdat, 0);
 		pgdat->kswapd_order = 0;
-		pgdat->kswapd_classzone_idx = 0;
+		pgdat->kswapd_classzone_idx = MAX_NR_ZONES;

 		ret = try_to_freeze();
 		if (kthread_should_stop())

@@ -3486,9 +3508,6 @@ static int kswapd(void *p)
 		reclaim_order = balance_pgdat(pgdat, alloc_order, classzone_idx);
 		if (reclaim_order < alloc_order)
 			goto kswapd_try_sleep;

If we fail order-5 request,  can we then give up order-5, and
try order-3 if requested, after napping?

That has no bearing upon this patch. At this point, kswapd has stopped
reclaiming at the requested order and is preparing to sleep. If there is
a parallel request for order-3 while it's sleeping, it'll wake and start
reclaiming at order-3 as requested.

-- 
Mel Gorman
SUSE Labs

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