The patch titled
Subject: mm: memcontrol: flush percpu vmstats before releasing memcg
has been added to the -mm tree. Its filename is
mm-memcontrol-flush-percpu-vmstats-before-releasing-memcg.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-memcontrol-flush-percpu-vmstats-before-releasing-memcg.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-memcontrol-flush-percpu-vmstats-before-releasing-memcg.patch
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------------------------------------------------------
From: Roman Gushchin <guro@xxxxxx>
Subject: mm: memcontrol: flush percpu vmstats before releasing memcg
Percpu caching of local vmstats with the conditional propagation by the
cgroup tree leads to an accumulation of errors on non-leaf levels.
Let's imagine two nested memory cgroups A and A/B. Say, a process
belonging to A/B allocates 100 pagecache pages on the CPU 0. The percpu
cache will spill 3 times, so that 32*3=96 pages will be accounted to A/B
and A atomic vmstat counters, 4 pages will remain in the percpu cache.
Imagine A/B is nearby memory.max, so that every following allocation
triggers a direct reclaim on the local CPU. Say, each such attempt will
free 16 pages on a new cpu. That means every percpu cache will have -16
pages, except the first one, which will have 4 - 16 = -12. A/B and A
atomic counters will not be touched at all.
Now a user removes A/B. All percpu caches are freed and corresponding
vmstat numbers are forgotten. A has 96 pages more than expected.
As memory cgroups are created and destroyed, errors do accumulate. Even
1-2 pages differences can accumulate into large numbers.
To fix this issue let's accumulate and propagate percpu vmstat values
before releasing the memory cgroup. At this point these numbers are
stable and cannot be changed.
Since on cpu hotplug we do flush percpu vmstats anyway, we can iterate
only over online cpus.
Link: http://lkml.kernel.org/r/20190812222911.2364802-2-guro@xxxxxx
Fixes: 42a300353577 ("mm: memcontrol: fix recursive statistics correctness & scalabilty")
Signed-off-by: Roman Gushchin <guro@xxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 40 ++++++++++++++++++++++++++++++++++++++++
1 file changed, 40 insertions(+)
--- a/mm/memcontrol.c~mm-memcontrol-flush-percpu-vmstats-before-releasing-memcg
+++ a/mm/memcontrol.c
@@ -3289,6 +3289,41 @@ static int memcg_online_kmem(struct mem_
return 0;
}
+static void memcg_flush_percpu_vmstats(struct mem_cgroup *memcg)
+{
+ unsigned long stat[MEMCG_NR_STAT];
+ struct mem_cgroup *mi;
+ int node, cpu, i;
+
+ for (i = 0; i < MEMCG_NR_STAT; i++)
+ stat[i] = 0;
+
+ for_each_online_cpu(cpu)
+ for (i = 0; i < MEMCG_NR_STAT; i++)
+ stat[i] += raw_cpu_read(memcg->vmstats_percpu->stat[i]);
+
+ for (mi = memcg; mi; mi = parent_mem_cgroup(mi))
+ for (i = 0; i < MEMCG_NR_STAT; i++)
+ atomic_long_add(stat[i], &mi->vmstats[i]);
+
+ for_each_node(node) {
+ struct mem_cgroup_per_node *pn = memcg->nodeinfo[node];
+ struct mem_cgroup_per_node *pi;
+
+ for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++)
+ stat[i] = 0;
+
+ for_each_online_cpu(cpu)
+ for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++)
+ stat[i] += raw_cpu_read(
+ pn->lruvec_stat_cpu->count[i]);
+
+ for (pi = pn; pi; pi = parent_nodeinfo(pi, node))
+ for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++)
+ atomic_long_add(stat[i], &pi->lruvec_stat[i]);
+ }
+}
+
static void memcg_offline_kmem(struct mem_cgroup *memcg)
{
struct cgroup_subsys_state *css;
@@ -4682,6 +4717,11 @@ static void __mem_cgroup_free(struct mem
{
int node;
+ /*
+ * Flush percpu vmstats to guarantee the value correctness
+ * on parent's and all ancestor levels.
+ */
+ memcg_flush_percpu_vmstats(memcg);
for_each_node(node)
free_mem_cgroup_per_node_info(memcg, node);
free_percpu(memcg->vmstats_percpu);
_
Patches currently in -mm which might be from guro@xxxxxx are
mm-workingset-fix-vmstat-counters-for-shadow-nodes.patch
mm-memcontrol-flush-percpu-vmstats-before-releasing-memcg.patch
mm-memcontrol-flush-percpu-slab-vmstats-on-kmem-offlining.patch
mm-memcontrol-switch-to-rcu-protection-in-drain_all_stock.patch
