[PATCH] NOT READY YET - just compile tested

[Michal Hocko]

memcg: remove memcg from the reclaim iterators

Now that per-node-zone-priority iterator caches memory cgroups rather
than their css ids we have to be careful and remove them from the
iterator when they are on the way out otherwise they might hang for
unbounded amount of time (until the global reclaim triggers the zone
under priority to find out the group is dead and let it to find the
final rest).

This is solved by hooking into mem_cgroup_pre_destroy and checking all
per-node-zone-priority iterators. If the current memcg is found in
iter->last_visited then it is replaced by its left sibling or its parent
otherwise. This guarantees that no group gets more reclaiming than
necessary and the next iteration will continue seemingly.

Spotted-by: Ying Han <yinghan@xxxxxxxxxx>
Not-signed-off-by-yet: Michal Hocko <mhocko@xxxxxxx>
---
 mm/memcontrol.c |   38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 7134148..286db74 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6213,12 +6213,50 @@ free_out:
 	return ERR_PTR(error);
 }
 
+static void mem_cgroup_remove_cached(struct mem_cgroup *memcg)
+{
+	int node, zone;
+
+	for_each_node(node) {
+		struct mem_cgroup_per_node *pn = memcg->info.nodeinfo[node];
+		int prio;
+
+		for (zone = 0; zone < MAX_NR_ZONES; zone++) {
+			struct mem_cgroup_per_zone *mz;
+
+			mz = &pn->zoneinfo[zone];
+			for (prio = 0; prio < DEF_PRIORITY + 1; prio++) {
+				struct mem_cgroup_reclaim_iter *iter;
+
+				iter = &mz->reclaim_iter[prio];
+				rcu_read_lock();
+				spin_lock(&iter->iter_lock);
+				if (iter->last_visited == memcg) {
+					struct cgroup *cgroup, *prev;
+
+					cgroup = memcg->css.cgroup;
+					prev = list_entry_rcu(cgroup->sibling.prev, struct cgroup, sibling);
+					if (&prev->sibling == &prev->parent->children)
+						prev = prev->parent;
+					iter->last_visited = mem_cgroup_from_cont(prev);
+
+					/* TODO can we do this? */
+					css_put(&memcg->css);
+				}
+				spin_unlock(&iter->iter_lock);
+				rcu_read_unlock();
+			}
+		}
+	}
+}
+
 static void mem_cgroup_pre_destroy(struct cgroup *cont)
 {
 	struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
 
 	mem_cgroup_reparent_charges(memcg);
 	mem_cgroup_destroy_all_caches(memcg);
+	mem_cgroup_remove_cached(memcg);
 }
 
 static void mem_cgroup_destroy(struct cgroup *cont)
-- 
1.7.10.4

-- 
Michal Hocko
SUSE Labs
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