From nobody Mon Feb 9 17:58:50 2026 Received: from out-172.mta1.migadu.com (out-172.mta1.migadu.com [95.215.58.172]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 501A73921CE for ; Thu, 5 Feb 2026 09:05:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.172 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770282334; cv=none; b=n2SD1eMsWu0Ei/IHxN2EeNpmGFrp70WH5VzSW1nMcbTFUi0h7gUmRQB0uRx4z/jWawS/IFdzt7FhMplAlrS5SZ19zu/tZNsiB527wxHjfwots0Zj5CqU+uKcURIBRmU4dr6azswDk9X0qMpeKa2s6qddVU9PdoyrFuow/1ZzGdI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770282334; c=relaxed/simple; bh=UuWnaWWqMbdHiYuNjBBXOZBTbbmmVtMidWSYsUiLjtY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=K/vjthX4V6QJ/P3HpkRqyj62C875uJChnhpp3qmJj3QCP6oikGZYd6QLG+/IGzHCruticTSGu0gYvsa3YgH2JG2zI0yMyqVhK7ufbbYIq+IARnkjeUMAxnTJp7iXm+YGkj66yhpYaCC4D5UEMn1swH9TGqt9A4o4JjIe63fHyD4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=cEFBJBp4; arc=none smtp.client-ip=95.215.58.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="cEFBJBp4" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1770282332; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Q5kLmp7dpf/L0kz6scIBO58rmstn0CFdVVhrJfMBpSg=; b=cEFBJBp4fsTuERx8Stl5wVqoVd8E28YddbNBPlGZQpsWhshWUmhrZhkCbV82uRiXOLhIw5 UyPwIXtYzd7wC5YsAMSw33sDBFwfI88TA8DSAxt3zZrGegp7SUF3MYRYpPRvFIV1h7xsPd F4YLuyhLUaPpe/JhULVpOT8604x/eto= From: Qi Zheng To: hannes@cmpxchg.org, hughd@google.com, mhocko@suse.com, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, david@kernel.org, lorenzo.stoakes@oracle.com, ziy@nvidia.com, harry.yoo@oracle.com, yosry.ahmed@linux.dev, imran.f.khan@oracle.com, kamalesh.babulal@oracle.com, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, chenridong@huaweicloud.com, mkoutny@suse.com, akpm@linux-foundation.org, hamzamahfooz@linux.microsoft.com, apais@linux.microsoft.com, lance.yang@linux.dev, bhe@redhat.com Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Qi Zheng Subject: [PATCH v4 29/31] mm: memcontrol: prepare for reparenting non-hierarchical stats Date: Thu, 5 Feb 2026 17:01:48 +0800 Message-ID: <3ca234c643ecb484f17aa88187e0bce8949bdb6b.1770279888.git.zhengqi.arch@bytedance.com> In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset="utf-8" From: Qi Zheng 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() 3. change these non-hierarchical stats to atomic_long_t type to avoid race between mem_cgroup_stat_aggregate() and reparent_state_local() Signed-off-by: Qi Zheng --- include/linux/memcontrol.h | 4 ++ kernel/cgroup/cgroup.c | 8 +-- mm/memcontrol-v1.c | 16 ++++++ mm/memcontrol-v1.h | 3 + mm/memcontrol.c | 113 ++++++++++++++++++++++++++++++++++--- 5 files changed, 132 insertions(+), 12 deletions(-) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 3970c102fe741..a4f6ab7eb98d6 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -957,12 +957,16 @@ static inline void mod_memcg_page_state(struct page *= page, =20 unsigned long memcg_events(struct mem_cgroup *memcg, int event); unsigned long memcg_page_state(struct mem_cgroup *memcg, int idx); +void reparent_memcg_state_local(struct mem_cgroup *memcg, + struct mem_cgroup *parent, int idx); unsigned long memcg_page_state_output(struct mem_cgroup *memcg, int item); bool memcg_stat_item_valid(int idx); bool memcg_vm_event_item_valid(enum vm_event_item idx); unsigned long lruvec_page_state(struct lruvec *lruvec, enum node_stat_item= idx); unsigned long lruvec_page_state_local(struct lruvec *lruvec, enum node_stat_item idx); +void reparent_memcg_lruvec_state_local(struct mem_cgroup *memcg, + struct mem_cgroup *parent, int idx); =20 void mem_cgroup_flush_stats(struct mem_cgroup *memcg); void mem_cgroup_flush_stats_ratelimited(struct mem_cgroup *memcg); diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 94788bd1fdf0e..dbf94a77018e6 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -6043,8 +6043,8 @@ 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 =3D - container_of(work, struct cgroup_subsys_state, destroy_work); + struct cgroup_subsys_state *css =3D container_of(to_rcu_work(work), + struct cgroup_subsys_state, destroy_rwork); =20 cgroup_lock(); =20 @@ -6065,8 +6065,8 @@ static void css_killed_ref_fn(struct percpu_ref *ref) container_of(ref, struct cgroup_subsys_state, refcnt); =20 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); } } =20 diff --git a/mm/memcontrol-v1.c b/mm/memcontrol-v1.c index c6078cd7f7e53..a427bb205763b 100644 --- a/mm/memcontrol-v1.c +++ b/mm/memcontrol-v1.c @@ -1887,6 +1887,22 @@ static const unsigned int memcg1_events[] =3D { PGMAJFAULT, }; =20 +void reparent_memcg1_state_local(struct mem_cgroup *memcg, struct mem_cgro= up *parent) +{ + int i; + + for (i =3D 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 m= em_cgroup *parent) +{ + int i; + + for (i =3D 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 eb3c3c1056574..45528195d3578 100644 --- a/mm/memcontrol-v1.h +++ b/mm/memcontrol-v1.h @@ -41,6 +41,7 @@ static inline bool do_memsw_account(void) =20 unsigned long memcg_events_local(struct mem_cgroup *memcg, int event); unsigned long memcg_page_state_local(struct mem_cgroup *memcg, int idx); +void mod_memcg_page_state_local(struct mem_cgroup *memcg, int idx, unsigne= d long val); unsigned long memcg_page_state_local_output(struct mem_cgroup *memcg, int = item); bool memcg1_alloc_events(struct mem_cgroup *memcg); void memcg1_free_events(struct mem_cgroup *memcg); @@ -73,6 +74,8 @@ void memcg1_uncharge_batch(struct mem_cgroup *memcg, unsi= gned long pgpgout, unsigned long nr_memory, int nid); =20 void memcg1_stat_format(struct mem_cgroup *memcg, struct seq_buf *s); +void reparent_memcg1_state_local(struct mem_cgroup *memcg, struct mem_cgro= up *parent); +void reparent_memcg1_lruvec_state_local(struct mem_cgroup *memcg, struct m= em_cgroup *parent); =20 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 c9b5dfd822d0a..e7d4e4ff411b6 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -225,6 +225,26 @@ static inline struct obj_cgroup *__memcg_reparent_objc= gs(struct mem_cgroup *memc return objcg; } =20 +#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 m= em_cgroup *parent) +{ + if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) + return; + + __mem_cgroup_flush_stats(memcg, true); + + /* The following counts are all non-hierarchical and need to be reparente= d. */ + reparent_memcg1_state_local(memcg, parent); + reparent_memcg1_lruvec_state_local(memcg, parent); +} +#else +static inline void reparent_state_local(struct mem_cgroup *memcg, struct m= em_cgroup *parent) +{ +} +#endif + static inline void reparent_locks(struct mem_cgroup *memcg, struct mem_cgr= oup *parent) { spin_lock_irq(&objcg_lock); @@ -407,7 +427,7 @@ struct lruvec_stats { long state[NR_MEMCG_NODE_STAT_ITEMS]; =20 /* Non-hierarchical (CPU aggregated) state */ - long state_local[NR_MEMCG_NODE_STAT_ITEMS]; + atomic_long_t state_local[NR_MEMCG_NODE_STAT_ITEMS]; =20 /* Pending child counts during tree propagation */ long state_pending[NR_MEMCG_NODE_STAT_ITEMS]; @@ -450,7 +470,7 @@ unsigned long lruvec_page_state_local(struct lruvec *lr= uvec, return 0; =20 pn =3D container_of(lruvec, struct mem_cgroup_per_node, lruvec); - x =3D READ_ONCE(pn->lruvec_stats->state_local[i]); + x =3D atomic_long_read(&(pn->lruvec_stats->state_local[i])); #ifdef CONFIG_SMP if (x < 0) x =3D 0; @@ -458,6 +478,27 @@ unsigned long lruvec_page_state_local(struct lruvec *l= ruvec, return x; } =20 +void reparent_memcg_lruvec_state_local(struct mem_cgroup *memcg, + struct mem_cgroup *parent, int idx) +{ + int i =3D memcg_stats_index(idx); + int nid; + + if (WARN_ONCE(BAD_STAT_IDX(i), "%s: missing stat item %d\n", __func__, id= x)) + return; + + for_each_node(nid) { + struct lruvec *child_lruvec =3D mem_cgroup_lruvec(memcg, NODE_DATA(nid)); + struct lruvec *parent_lruvec =3D mem_cgroup_lruvec(parent, NODE_DATA(nid= )); + struct mem_cgroup_per_node *parent_pn; + unsigned long value =3D lruvec_page_state_local(child_lruvec, idx); + + parent_pn =3D container_of(parent_lruvec, struct mem_cgroup_per_node, lr= uvec); + + atomic_long_add(value, &(parent_pn->lruvec_stats->state_local[i])); + } +} + /* Subset of vm_event_item to report for memcg event stats */ static const unsigned int memcg_vm_event_stat[] =3D { #ifdef CONFIG_MEMCG_V1 @@ -549,7 +590,7 @@ struct memcg_vmstats { unsigned long events[NR_MEMCG_EVENTS]; =20 /* Non-hierarchical (CPU aggregated) page state & events */ - long state_local[MEMCG_VMSTAT_SIZE]; + atomic_long_t state_local[MEMCG_VMSTAT_SIZE]; unsigned long events_local[NR_MEMCG_EVENTS]; =20 /* Pending child counts during tree propagation */ @@ -712,6 +753,42 @@ static int memcg_state_val_in_pages(int idx, int val) return max(val * unit / PAGE_SIZE, 1UL); } =20 +#ifdef CONFIG_MEMCG_V1 +/* + * Used in mod_memcg_state() and mod_memcg_lruvec_state() to avoid race wi= th + * reparenting of non-hierarchical state_locals. + */ +static inline struct mem_cgroup *get_non_dying_memcg_start(struct mem_cgro= up *memcg) +{ + if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) + return memcg; + + rcu_read_lock(); + + while (memcg_is_dying(memcg)) + memcg =3D 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_cgro= up *memcg) +{ + return memcg; +} + +static inline void get_non_dying_memcg_end(void) +{ +} +#endif + /** * mod_memcg_state - update cgroup memory statistics * @memcg: the memory cgroup @@ -750,13 +827,25 @@ unsigned long memcg_page_state_local(struct mem_cgrou= p *memcg, int idx) if (WARN_ONCE(BAD_STAT_IDX(i), "%s: missing stat item %d\n", __func__, id= x)) return 0; =20 - x =3D READ_ONCE(memcg->vmstats->state_local[i]); + x =3D atomic_long_read(&(memcg->vmstats->state_local[i])); #ifdef CONFIG_SMP if (x < 0) x =3D 0; #endif return x; } + +void reparent_memcg_state_local(struct mem_cgroup *memcg, + struct mem_cgroup *parent, int idx) +{ + int i =3D memcg_stats_index(idx); + unsigned long value =3D memcg_page_state_local(memcg, idx); + + if (WARN_ONCE(BAD_STAT_IDX(i), "%s: missing stat item %d\n", __func__, id= x)) + return; + + atomic_long_add(value, &(parent->vmstats->state_local[i])); +} #endif =20 static void mod_memcg_lruvec_state(struct lruvec *lruvec, @@ -4061,6 +4150,8 @@ struct aggregate_control { long *aggregate; /* pointer to the non-hierarchichal (CPU aggregated) counters */ long *local; + /* pointer to the atomic non-hierarchichal (CPU aggregated) counters */ + atomic_long_t *alocal; /* pointer to the pending child counters during tree propagation */ long *pending; /* pointer to the parent's pending counters, could be NULL */ @@ -4098,8 +4189,12 @@ static void mem_cgroup_stat_aggregate(struct aggrega= te_control *ac) } =20 /* Aggregate counts on this level and propagate upwards */ - if (delta_cpu) - ac->local[i] +=3D delta_cpu; + if (delta_cpu) { + if (ac->local) + ac->local[i] +=3D delta_cpu; + else if (ac->alocal) + atomic_long_add(delta_cpu, &(ac->alocal[i])); + } =20 if (delta) { ac->aggregate[i] +=3D delta; @@ -4170,7 +4265,8 @@ static void mem_cgroup_css_rstat_flush(struct cgroup_= subsys_state *css, int cpu) =20 ac =3D (struct aggregate_control) { .aggregate =3D memcg->vmstats->state, - .local =3D memcg->vmstats->state_local, + .local =3D NULL, + .alocal =3D memcg->vmstats->state_local, .pending =3D memcg->vmstats->state_pending, .ppending =3D parent ? parent->vmstats->state_pending : NULL, .cstat =3D statc->state, @@ -4203,7 +4299,8 @@ static void mem_cgroup_css_rstat_flush(struct cgroup_= subsys_state *css, int cpu) =20 ac =3D (struct aggregate_control) { .aggregate =3D lstats->state, - .local =3D lstats->state_local, + .local =3D NULL, + .alocal =3D lstats->state_local, .pending =3D lstats->state_pending, .ppending =3D plstats ? plstats->state_pending : NULL, .cstat =3D lstatc->state, --=20 2.20.1