[RFC][PATCH 3/4] memcg: softlimit caller via kswapd

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

This patch adds hooks for memcg's softlimit to kswapd().

Softlimit handler is called...
  - before generic shrink_zone() is called.
  - # of pages to be scanned depends on priority.
  - If not enough progress, selected memcg will be moved to UNUSED queue.
  - at each call for balance_pgdat(), softlimit queue is rebalanced.

Changelog: v1->v2
  - check "enough progress" or not.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
 mm/vmscan.c |   42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

Index: develop/mm/vmscan.c
===================================================================
--- develop.orig/mm/vmscan.c
+++ develop/mm/vmscan.c
@@ -1733,6 +1733,43 @@ unsigned long try_to_free_mem_cgroup_pag
 }
 #endif
 
+static void shrink_zone_softlimit(struct scan_control *sc, struct zone *zone,
+			   int order, int priority, int target, int end_zone)
+{
+	int scan = SWAP_CLUSTER_MAX;
+	int nid = zone->zone_pgdat->node_id;
+	int zid = zone_idx(zone);
+	int before;
+	struct mem_cgroup *mem;
+
+	scan <<= (DEF_PRIORITY - priority);
+	if (scan > (target * 2))
+		scan = target * 2;
+
+	while (scan > 0) {
+		if (zone_watermark_ok(zone, order, target, end_zone, 0))
+			break;
+		mem = mem_cgroup_schedule(nid, zid);
+		if (!mem)
+			return;
+		sc->nr_scanned = 0;
+		sc->mem_cgroup = mem;
+		before = sc->nr_reclaimed;
+		sc->isolate_pages = mem_cgroup_isolate_pages;
+
+		shrink_zone(priority, zone, sc);
+
+		if (sc->nr_reclaimed - before > scan/2)
+			mem_cgroup_schedule_end(nid, zid, mem, true);
+		else
+			mem_cgroup_schedule_end(nid, zid, mem, false);
+
+		sc->mem_cgroup = NULL;
+		sc->isolate_pages = isolate_pages_global;
+		scan -= sc->nr_scanned;
+	}
+	return;
+}
 /*
  * For kswapd, balance_pgdat() will work across all this node's zones until
  * they are all at pages_high.
@@ -1776,6 +1813,8 @@ static unsigned long balance_pgdat(pg_da
 	 */
 	int temp_priority[MAX_NR_ZONES];
 
+	/* Refill softlimit queue */
+	mem_cgroup_reschedule(pgdat->node_id);
 loop_again:
 	total_scanned = 0;
 	sc.nr_reclaimed = 0;
@@ -1856,6 +1895,9 @@ loop_again:
 					       end_zone, 0))
 				all_zones_ok = 0;
 			temp_priority[i] = priority;
+			/* Try soft limit at first */
+			shrink_zone_softlimit(&sc, zone, order, priority,
+					       8 * zone->pages_high, end_zone);
 			sc.nr_scanned = 0;
 			note_zone_scanning_priority(zone, priority);
 			/*

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