[PATCH v6 30/33] mm: memcontrol: prepare for reparenting non-hierarchical stats

[Qi Zheng <qi.zheng@linux.dev>]

From: Qi Zheng <zhengqi.arch@bytedance.com>

To resolve the dying memcg issue, we need to reparent LRU folios of child
memcg to its parent memcg. This could cause problems for non-hierarchical
stats.

As Yosry Ahmed pointed out:

```
In short, if memory is charged to a dying cgroup at the time of
reparenting, when the memory gets uncharged the stats updates will occur
at the parent. This will update both hierarchical and non-hierarchical
stats of the parent, which would corrupt the parent's non-hierarchical
stats (because those counters were never incremented when the memory was
charged).
```

Now we have the following two types of non-hierarchical stats, and they
are only used in CONFIG_MEMCG_V1:

a. memcg->vmstats->state_local[i]
b. pn->lruvec_stats->state_local[i]

To ensure that these non-hierarchical stats work properly, we need to
reparent these non-hierarchical stats after reparenting LRU folios. To
this end, this commit makes the following preparations:

1. implement reparent_state_local() to reparent non-hierarchical stats
2. make css_killed_work_fn() to be called in rcu work, and implement
   get_non_dying_memcg_start() and get_non_dying_memcg_end() to avoid race
   between mod_memcg_state()/mod_memcg_lruvec_state()
   and reparent_state_local()

Co-developed-by: Yosry Ahmed <yosry@kernel.org>
Signed-off-by: Yosry Ahmed <yosry@kernel.org>
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
---
 kernel/cgroup/cgroup.c |  9 ++--
 mm/memcontrol-v1.c     | 16 +++++++
 mm/memcontrol-v1.h     |  7 +++
 mm/memcontrol.c        | 97 ++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 125 insertions(+), 4 deletions(-)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index be1d71dda3179..a9007f8aa029e 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -6044,8 +6044,9 @@ int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name, umode_t mode)
  */
 static void css_killed_work_fn(struct work_struct *work)
 {
-	struct cgroup_subsys_state *css =
-		container_of(work, struct cgroup_subsys_state, destroy_work);
+	struct cgroup_subsys_state *css;
+
+	css = container_of(to_rcu_work(work), struct cgroup_subsys_state, destroy_rwork);
 
 	cgroup_lock();
 
@@ -6066,8 +6067,8 @@ static void css_killed_ref_fn(struct percpu_ref *ref)
 		container_of(ref, struct cgroup_subsys_state, refcnt);
 
 	if (atomic_dec_and_test(&css->online_cnt)) {
-		INIT_WORK(&css->destroy_work, css_killed_work_fn);
-		queue_work(cgroup_offline_wq, &css->destroy_work);
+		INIT_RCU_WORK(&css->destroy_rwork, css_killed_work_fn);
+		queue_rcu_work(cgroup_offline_wq, &css->destroy_rwork);
 	}
 }
 
diff --git a/mm/memcontrol-v1.c b/mm/memcontrol-v1.c
index fe42ef664f1e1..51fb4406f45cf 100644
--- a/mm/memcontrol-v1.c
+++ b/mm/memcontrol-v1.c
@@ -1897,6 +1897,22 @@ static const unsigned int memcg1_events[] = {
 	PGMAJFAULT,
 };
 
+void reparent_memcg1_state_local(struct mem_cgroup *memcg, struct mem_cgroup *parent)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(memcg1_stats); i++)
+		reparent_memcg_state_local(memcg, parent, memcg1_stats[i]);
+}
+
+void reparent_memcg1_lruvec_state_local(struct mem_cgroup *memcg, struct mem_cgroup *parent)
+{
+	int i;
+
+	for (i = 0; i < NR_LRU_LISTS; i++)
+		reparent_memcg_lruvec_state_local(memcg, parent, i);
+}
+
 void memcg1_stat_format(struct mem_cgroup *memcg, struct seq_buf *s)
 {
 	unsigned long memory, memsw;
diff --git a/mm/memcontrol-v1.h b/mm/memcontrol-v1.h
index 4041b5027a94b..05e6ff40f7556 100644
--- a/mm/memcontrol-v1.h
+++ b/mm/memcontrol-v1.h
@@ -77,6 +77,13 @@ void memcg1_uncharge_batch(struct mem_cgroup *memcg, unsigned long pgpgout,
 			   unsigned long nr_memory, int nid);
 
 void memcg1_stat_format(struct mem_cgroup *memcg, struct seq_buf *s);
+void reparent_memcg1_state_local(struct mem_cgroup *memcg, struct mem_cgroup *parent);
+void reparent_memcg1_lruvec_state_local(struct mem_cgroup *memcg, struct mem_cgroup *parent);
+
+void reparent_memcg_state_local(struct mem_cgroup *memcg,
+				struct mem_cgroup *parent, int idx);
+void reparent_memcg_lruvec_state_local(struct mem_cgroup *memcg,
+				       struct mem_cgroup *parent, int idx);
 
 void memcg1_account_kmem(struct mem_cgroup *memcg, int nr_pages);
 static inline bool memcg1_tcpmem_active(struct mem_cgroup *memcg)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 23b70bd80ddc9..b0519a16f5684 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -226,6 +226,34 @@ static inline struct obj_cgroup *__memcg_reparent_objcgs(struct mem_cgroup *memc
 	return objcg;
 }
 
+#ifdef CONFIG_MEMCG_V1
+static void __mem_cgroup_flush_stats(struct mem_cgroup *memcg, bool force);
+
+static inline void reparent_state_local(struct mem_cgroup *memcg, struct mem_cgroup *parent)
+{
+	if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
+		return;
+
+	/*
+	 * Reparent stats exposed non-hierarchically. Flush @memcg's stats first
+	 * to read its stats accurately , and conservatively flush @parent's
+	 * stats after reparenting to avoid hiding a potentially large stat
+	 * update (e.g. from callers of mem_cgroup_flush_stats_ratelimited()).
+	 */
+	__mem_cgroup_flush_stats(memcg, true);
+
+	/* The following counts are all non-hierarchical and need to be reparented. */
+	reparent_memcg1_state_local(memcg, parent);
+	reparent_memcg1_lruvec_state_local(memcg, parent);
+
+	__mem_cgroup_flush_stats(parent, true);
+}
+#else
+static inline void reparent_state_local(struct mem_cgroup *memcg, struct mem_cgroup *parent)
+{
+}
+#endif
+
 static inline void reparent_locks(struct mem_cgroup *memcg, struct mem_cgroup *parent)
 {
 	spin_lock_irq(&objcg_lock);
@@ -473,6 +501,30 @@ unsigned long lruvec_page_state_local(struct lruvec *lruvec,
 	return x;
 }
 
+#ifdef CONFIG_MEMCG_V1
+static void __mod_memcg_lruvec_state(struct mem_cgroup_per_node *pn,
+				     enum node_stat_item idx, int val);
+
+void reparent_memcg_lruvec_state_local(struct mem_cgroup *memcg,
+				       struct mem_cgroup *parent, int idx)
+{
+	int nid;
+
+	for_each_node(nid) {
+		struct lruvec *child_lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(nid));
+		struct lruvec *parent_lruvec = mem_cgroup_lruvec(parent, NODE_DATA(nid));
+		unsigned long value = lruvec_page_state_local(child_lruvec, idx);
+		struct mem_cgroup_per_node *child_pn, *parent_pn;
+
+		child_pn = container_of(child_lruvec, struct mem_cgroup_per_node, lruvec);
+		parent_pn = container_of(parent_lruvec, struct mem_cgroup_per_node, lruvec);
+
+		__mod_memcg_lruvec_state(child_pn, idx, -value);
+		__mod_memcg_lruvec_state(parent_pn, idx, value);
+	}
+}
+#endif
+
 /* Subset of vm_event_item to report for memcg event stats */
 static const unsigned int memcg_vm_event_stat[] = {
 #ifdef CONFIG_MEMCG_V1
@@ -718,6 +770,42 @@ static int memcg_state_val_in_pages(int idx, int val)
 		return max(val * unit / PAGE_SIZE, 1UL);
 }
 
+#ifdef CONFIG_MEMCG_V1
+/*
+ * Used in mod_memcg_state() and mod_memcg_lruvec_state() to avoid race with
+ * reparenting of non-hierarchical state_locals.
+ */
+static inline struct mem_cgroup *get_non_dying_memcg_start(struct mem_cgroup *memcg)
+{
+	if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
+		return memcg;
+
+	rcu_read_lock();
+
+	while (memcg_is_dying(memcg))
+		memcg = parent_mem_cgroup(memcg);
+
+	return memcg;
+}
+
+static inline void get_non_dying_memcg_end(void)
+{
+	if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
+		return;
+
+	rcu_read_unlock();
+}
+#else
+static inline struct mem_cgroup *get_non_dying_memcg_start(struct mem_cgroup *memcg)
+{
+	return memcg;
+}
+
+static inline void get_non_dying_memcg_end(void)
+{
+}
+#endif
+
 static void __mod_memcg_state(struct mem_cgroup *memcg,
 			      enum memcg_stat_item idx, int val)
 {
@@ -769,6 +857,15 @@ unsigned long memcg_page_state_local(struct mem_cgroup *memcg, int idx)
 #endif
 	return x;
 }
+
+void reparent_memcg_state_local(struct mem_cgroup *memcg,
+				struct mem_cgroup *parent, int idx)
+{
+	unsigned long value = memcg_page_state_local(memcg, idx);
+
+	__mod_memcg_state(memcg, idx, -value);
+	__mod_memcg_state(parent, idx, value);
+}
 #endif
 
 static void __mod_memcg_lruvec_state(struct mem_cgroup_per_node *pn,
-- 
2.20.1