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Message-ID: <20230320030648.50663-2-caixinchen1@huawei.com>
Date: Mon, 20 Mar 2023 03:06:48 +0000
From: Cai Xinchen <caixinchen1@...wei.com>
To: <songmuchun@...edance.com>, <akpm@...ux-foundation.org>,
<hannes@...xchg.org>, <longman@...hat.com>, <mhocko@...nel.org>,
<roman.gushchin@...ux.dev>, <shakeelb@...gle.com>
CC: <cgroups@...r.kernel.org>, <duanxiongchun@...edance.com>,
<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
<yosryahmed@...gle.com>, <mpenttil@...hat.com>
Subject: [PATCH 1/1] mm: memcontrol: fix vmstats_percpu state incorrect subtraction after reparent
When memcg C is offllined, its pages are reparented to memcg P,
so far P->vmstats (hierarchical) have those pages, and
P->vmstats_percpu (non-hierarchical) don't. When those pages get
uncharged, P->vmstats (hierachical) decreases, which is correct,
but P->vmstats_percpu (non-hierarchical) also decreases, which
is wrong, as those stats were never added to P->vmstats_percpu to
begin with. If the reparented memory exceeds the original
non-hierarchical memory in P, some arg such as cache which is shown
in memory.stat will be zero (if x < 0, it shows 0)
To solve this problem, after reparent memcg, we should use
cgroup_rstat_updated to add cgrp to rstat updated tree, and then after
css refcount == 0, cgroup_rstat_flush is called by css_release_work_fn
and css->flags is set as CSS_RELEASED. We propagate state in
vmstat_percpu of struct mem_cgroup to its parent if css->flags is
CSS_RELEASED. We use reparent_state to record those state and
reparent_tag to ensure propagate vmstats_percpu of dying memcg only
once. When mem_cgroup_css_rstat_flush is called, we
add reparent_state to parent_memcg->vmstats_percpu->state and
memcg->vmstgats_percpu->state_prev in locked context. The delta
between state and state_prev would not change. So some accumulative
value of vmstats_percpu (such as cache in memory.stat) will be
shown correctly. And this patch does not produce delta between state
and state_prev in vmstats_percpu which will be added to vmstats.
Signed-off-by: Cai Xinchen <caixinchen1@...wei.com>
---
kernel/cgroup/cgroup.c | 5 +++++
mm/memcontrol.c | 43 +++++++++++++++++++++++++++++++++++++++++-
2 files changed, 47 insertions(+), 1 deletion(-)
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 935e8121b21e..11138ee09a61 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -5384,12 +5384,17 @@ static void css_release_work_fn(struct work_struct *work)
container_of(work, struct cgroup_subsys_state, destroy_work);
struct cgroup_subsys *ss = css->ss;
struct cgroup *cgrp = css->cgroup;
+ int cpu;
mutex_lock(&cgroup_mutex);
css->flags |= CSS_RELEASED;
list_del_rcu(&css->sibling);
+ /* update all cgrp rstat because reparent rstat flush */
+ for_each_possible_cpu(cpu)
+ cgroup_rstat_updated(cgrp, cpu);
+
if (ss) {
/* css release path */
if (!list_empty(&css->rstat_css_node)) {
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 77929d08c8c9..658d42dc9820 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -842,6 +842,9 @@ struct memcg_vmstats_percpu {
/* Cgroup1: threshold notifications & softlimit tree updates */
unsigned long nr_page_events;
unsigned long targets[MEM_CGROUP_NTARGETS];
+
+ /* Tag for propagate vmstat_percpu, 1 for start, 0 for stop */
+ long reparent_tag;
};
struct memcg_vmstats {
@@ -852,6 +855,9 @@ struct memcg_vmstats {
/* Pending child counts during tree propagation */
long state_pending[MEMCG_NR_STAT];
unsigned long events_pending[NR_MEMCG_EVENTS];
+
+ /* Propagate vmstat_percpu after reparent */
+ long reparent_state[MEMCG_NR_STAT];
};
unsigned long memcg_page_state(struct mem_cgroup *memcg, int idx)
@@ -5558,6 +5564,17 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state *css)
return -ENOMEM;
}
+static void set_reparent_tag_for_vmstats(struct mem_cgroup *memcg)
+{
+ int cpu;
+ struct memcg_vmstats_percpu *statc;
+
+ for_each_possible_cpu(cpu) {
+ statc = per_cpu_ptr(memcg->vmstats_percpu, cpu);
+ WRITE_ONCE(statc->reparent_tag, 1);
+ }
+}
+
static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
{
struct mem_cgroup *memcg = mem_cgroup_from_css(css);
@@ -5579,6 +5596,7 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
page_counter_set_low(&memcg->memory, 0);
memcg_reparent_objcgs(memcg);
+ set_reparent_tag_for_vmstats(memcg);
memcg_offline_kmem(memcg);
reparent_shrinker_deferred(memcg);
wb_memcg_offline(memcg);
@@ -5653,8 +5671,9 @@ static void mem_cgroup_css_rstat_flush(struct cgroup_subsys_state *css, int cpu)
struct mem_cgroup *memcg = mem_cgroup_from_css(css);
struct mem_cgroup *parent = parent_mem_cgroup(memcg);
struct memcg_vmstats_percpu *statc;
- long delta, v;
+ long delta, v, reparent_v;
int i, nid;
+ bool reparent = false;
statc = per_cpu_ptr(memcg->vmstats_percpu, cpu);
@@ -5668,6 +5687,10 @@ static void mem_cgroup_css_rstat_flush(struct cgroup_subsys_state *css, int cpu)
if (delta)
memcg->vmstats->state_pending[i] = 0;
+ reparent_v = memcg->vmstats->reparent_state[i];
+ if (reparent_v)
+ memcg->vmstats->reparent_state[i] = 0;
+
/* Add CPU changes on this level since the last flush */
v = READ_ONCE(statc->state[i]);
if (v != statc->state_prev[i]) {
@@ -5675,6 +5698,21 @@ static void mem_cgroup_css_rstat_flush(struct cgroup_subsys_state *css, int cpu)
statc->state_prev[i] = v;
}
+ /* if reparent tag is set, this cgroup is offline and reparent.
+ * if css->flags & CSS_RELEASED, this cgroup will be released
+ * soon. We should propagate memcg's vmstats_percpu to its parent.
+ */
+ if (READ_ONCE(statc->reparent_tag) &&
+ css->flags & CSS_RELEASED && parent) {
+ parent->vmstats->reparent_state[i] += v + reparent_v;
+ reparent = true;
+ } else if (reparent_v) {
+ __this_cpu_add(memcg->vmstats_percpu->state[i],
+ reparent_v);
+ __this_cpu_add(memcg->vmstats_percpu->state_prev[i],
+ reparent_v);
+ }
+
if (!delta)
continue;
@@ -5684,6 +5722,9 @@ static void mem_cgroup_css_rstat_flush(struct cgroup_subsys_state *css, int cpu)
parent->vmstats->state_pending[i] += delta;
}
+ if (reparent)
+ WRITE_ONCE(statc->reparent_tag, 0);
+
for (i = 0; i < NR_MEMCG_EVENTS; i++) {
delta = memcg->vmstats->events_pending[i];
if (delta)
--
2.17.1
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