Apply changes noted by Jernej in #219

patch/kernel/sun8i-default/fix-kswapd.patch

@@ -0,0 +1,73 @@
+diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
+index a2bbaef..06f8e38 100644
+--- a/include/linux/vm_event_item.h
++++ b/include/linux/vm_event_item.h
+@@ -35,6 +35,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
+ #endif
+ 		PGINODESTEAL, SLABS_SCANNED, KSWAPD_INODESTEAL,
+ 		KSWAPD_LOW_WMARK_HIT_QUICKLY, KSWAPD_HIGH_WMARK_HIT_QUICKLY,
++		KSWAPD_SKIP_CONGESTION_WAIT,
+ 		PAGEOUTRUN, ALLOCSTALL, PGROTATED,
+ #ifdef CONFIG_COMPACTION
+ 		COMPACTBLOCKS, COMPACTPAGES, COMPACTPAGEFAILED,
+diff --git a/mm/vmstat.c b/mm/vmstat.c
+index 1de03bf..1034ebc 100644
+--- a/mm/vmstat.c
++++ b/mm/vmstat.c
+@@ -758,6 +758,7 @@ const char * const vmstat_text[] = {
+ 	"kswapd_inodesteal",
+ 	"kswapd_low_wmark_hit_quickly",
+ 	"kswapd_high_wmark_hit_quickly",
++	"kswapd_skip_congestion_wait",
+ 	"pageoutrun",
+ 	"allocstall",
+
+diff --git a/mm/vmscan.c b/mm/vmscan.c
+index db61d7f..d6b0e39 100755
+--- a/mm/vmscan.c
++++ b/mm/vmscan.c
+@@ -2782,6 +2782,7 @@ loop_again:
+
+ 	for (priority = DEF_PRIORITY; priority >= 0; priority--) {
+ 		unsigned long lru_pages = 0;
++		int has_under_min_watermark_zone = 0;
+
+ 		/* The swap token gets in the way of swapout... */
+ 		if (!priority)
+@@ -2923,7 +2924,17 @@ loop_again:
+ 				continue;
+ 			}
+
+-			if (zone_balanced(zone, testorder, 0, end_zone)) {
++			if (!zone_balanced(zone, testorder, 0, end_zone)) {
++				all_zones_ok = 0;
++				/*
++				 * We are still under min water mark.  This
++				 * means that we have a GFP_ATOMIC allocation
++				 * failure risk. Hurry up!
++				 */
++				if (!zone_watermark_ok_safe(zone, order,
++					    min_wmark_pages(zone), end_zone, 0))
++					has_under_min_watermark_zone = 1;
++			} else {
+ 				/*
+ 				 * If a zone reaches its high watermark,
+ 				 * consider it to be no longer congested. It's
+@@ -2940,6 +2951,17 @@ loop_again:
+ 		if (all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))
+ 			break;		/* kswapd: all done */
+ 		/*
++		 * OK, kswapd is getting into trouble.  Take a nap, then take
++		 * another pass across the zones.
++		 */
++		if (total_scanned && (priority < DEF_PRIORITY - 2)) {
++			if (has_under_min_watermark_zone)
++				count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT);
++			else
++				congestion_wait(BLK_RW_ASYNC, HZ/10);
++		}
++
++		/*
+ 		 * We do this so kswapd doesn't build up large priorities for
+ 		 * example when it is freeing in parallel with allocators. It
+ 		 * matches the direct reclaim path behaviour in terms of impact