[PATCH 5.2 149/162] mm: memcontrol: flush percpu vmevents before releasing memcg

[Greg Kroah-Hartman]

From: Roman Gushchin <guro@xxxxxx>

commit bb65f89b7d3d305c14951f49860711fbcae70692 upstream.

Similar to vmstats, percpu caching of local vmevents leads to an
accumulation of errors on non-leaf levels.  This happens because some
leftovers may remain in percpu caches, so that they are never propagated
up by the cgroup tree and just disappear into nonexistence with on
releasing of the memory cgroup.

To fix this issue let's accumulate and propagate percpu vmevents values
before releasing the memory cgroup similar to what we're doing with
vmstats.

Since on cpu hotplug we do flush percpu vmstats anyway, we can iterate
only over online cpus.

Link: http://lkml.kernel.org/r/20190819202338.363363-4-guro@xxxxxx
Fixes: 42a300353577 ("mm: memcontrol: fix recursive statistics correctness & scalabilty")
Signed-off-by: Roman Gushchin <guro@xxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 mm/memcontrol.c |   22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3185,6 +3185,25 @@ static void memcg_flush_percpu_vmstats(s
 	}
 }
 
+static void memcg_flush_percpu_vmevents(struct mem_cgroup *memcg)
+{
+	unsigned long events[NR_VM_EVENT_ITEMS];
+	struct mem_cgroup *mi;
+	int cpu, i;
+
+	for (i = 0; i < NR_VM_EVENT_ITEMS; i++)
+		events[i] = 0;
+
+	for_each_online_cpu(cpu)
+		for (i = 0; i < NR_VM_EVENT_ITEMS; i++)
+			events[i] += raw_cpu_read(
+				memcg->vmstats_percpu->events[i]);
+
+	for (mi = memcg; mi; mi = parent_mem_cgroup(mi))
+		for (i = 0; i < NR_VM_EVENT_ITEMS; i++)
+			atomic_long_add(events[i], &mi->vmevents[i]);
+}
+
 #ifdef CONFIG_MEMCG_KMEM
 static int memcg_online_kmem(struct mem_cgroup *memcg)
 {
@@ -4587,10 +4606,11 @@ static void __mem_cgroup_free(struct mem
 	int node;
 
 	/*
-	 * Flush percpu vmstats to guarantee the value correctness
+	 * Flush percpu vmstats and vmevents to guarantee the value correctness
 	 * on parent's and all ancestor levels.
 	 */
 	memcg_flush_percpu_vmstats(memcg);
+	memcg_flush_percpu_vmevents(memcg);
 	for_each_node(node)
 		free_mem_cgroup_per_node_info(memcg, node);
 	free_percpu(memcg->vmstats_percpu);