[PATCH 2/3] mm/vmscan: Enable kswapd to reclaim low-protected memory

[Xunlei Pang <xlpang@linux.alibaba.com>]

There may be cgroup memory overcommitment, it will become
even common in the future.

Let's enable kswapd to reclaim low-protected memory in case
of memory pressure, to mitigate the global direct reclaim
pressures which could cause jitters to the response time of
lantency-sensitive groups.

Signed-off-by: Xunlei Pang <xlpang@linux.alibaba.com>
---
 mm/vmscan.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 62ac0c488624..3d412eb91f73 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3531,6 +3531,7 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
 
 	count_vm_event(PAGEOUTRUN);
 
+retry:
 	do {
 		unsigned long nr_reclaimed = sc.nr_reclaimed;
 		bool raise_priority = true;
@@ -3622,6 +3623,13 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
 			sc.priority--;
 	} while (sc.priority >= 1);
 
+	if (!sc.nr_reclaimed && sc.memcg_low_skipped) {
+		sc.priority = DEF_PRIORITY;
+		sc.memcg_low_reclaim = 1;
+		sc.memcg_low_skipped = 0;
+		goto retry;
+	}
+
 	if (!sc.nr_reclaimed)
 		pgdat->kswapd_failures++;
 
-- 
2.13.5 (Apple Git-94)