From nobody Thu Apr 2 00:09:21 2026 Received: from out-179.mta0.migadu.com (out-179.mta0.migadu.com [91.218.175.179]) (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 ACEDD396D30 for ; Thu, 5 Mar 2026 11:59:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.179 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772711973; cv=none; b=IlfUwUDV61ip+OaN6g964tfuhlFHVqjGXYG2cfGdMYCdlDcxat+EOj7KHEw3JWysIB05OaZOBdCkqJbXP0PuGTCrgmTd4/TRfikXtgE7r3/8mMs8IkZG6T8X5r1kYOYM1ArmbxSF3qa904EkQAc8nzO9PY+iyzCPWtpFJIx9sVA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772711973; c=relaxed/simple; bh=T46f9lJNGeYk9fE7qlzG8IF0YxUcD2tczF2uwxI7cXQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Tec6nkicZqYxNmVdCYkIFVBXMHbcnavD9+G0ALmKta9ogAt4B/XXxrtojlp6K0oyuF2/y/OAq0ODf9vjkjnF9kJ+yEouL2WOq/2sgtasng/W3jgYq9CbKL+zmU5I96OgUcSkx9K1trFWv9uiW66LAzVCHzxwx5LnDY5Nu9Y6SkA= 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=a7n0Qy4E; arc=none smtp.client-ip=91.218.175.179 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="a7n0Qy4E" 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=1772711969; 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=HqFrQFPtVkdFa+x5udaTTR/4bek6Z3abiEm6Dfccfmw=; b=a7n0Qy4ENXJeEguCWvjqw9nNjrrdnQOqZiHKBtpkL8SsI21/hCDrzAK2ROURwoVSSdMwDH XF0k4a5wB/cMBuVNR1A9uD5UuJdzQ2ZyymrWWsaXZJYoq403esAMzDgzyZziG+fE7mvHZW S2GFZdcxiy7m82Ucvc5wnHOANDKGvR4= 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, usamaarif642@gmail.com Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Qi Zheng , Yosry Ahmed Subject: [PATCH v6 30/33] mm: memcontrol: prepare for reparenting non-hierarchical stats Date: Thu, 5 Mar 2026 19:52:48 +0800 Message-ID: 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() Co-developed-by: Yosry Ahmed Signed-off-by: Yosry Ahmed Signed-off-by: Qi Zheng Acked-by: Shakeel Butt --- 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 =3D - container_of(work, struct cgroup_subsys_state, destroy_work); + struct cgroup_subsys_state *css; + + css =3D container_of(to_rcu_work(work), struct cgroup_subsys_state, destr= oy_rwork); =20 cgroup_lock(); =20 @@ -6066,8 +6067,8 @@ 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 fe42ef664f1e1..51fb4406f45cf 100644 --- a/mm/memcontrol-v1.c +++ b/mm/memcontrol-v1.c @@ -1897,6 +1897,22 @@ 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 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, uns= igned 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); + +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); =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 23b70bd80ddc9..b0519a16f5684 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -226,6 +226,34 @@ 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; + + /* + * 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 reparente= d. */ + 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 m= em_cgroup *parent) +{ +} +#endif + static inline void reparent_locks(struct mem_cgroup *memcg, struct mem_cgr= oup *parent) { spin_lock_irq(&objcg_lock); @@ -473,6 +501,30 @@ unsigned long lruvec_page_state_local(struct lruvec *l= ruvec, return x; } =20 +#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 =3D mem_cgroup_lruvec(memcg, NODE_DATA(nid)); + struct lruvec *parent_lruvec =3D mem_cgroup_lruvec(parent, NODE_DATA(nid= )); + unsigned long value =3D lruvec_page_state_local(child_lruvec, idx); + struct mem_cgroup_per_node *child_pn, *parent_pn; + + child_pn =3D container_of(child_lruvec, struct mem_cgroup_per_node, lruv= ec); + parent_pn =3D container_of(parent_lruvec, struct mem_cgroup_per_node, lr= uvec); + + __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[] =3D { #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); } =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 + 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 =3D memcg_page_state_local(memcg, idx); + + __mod_memcg_state(memcg, idx, -value); + __mod_memcg_state(parent, idx, value); +} #endif =20 static void __mod_memcg_lruvec_state(struct mem_cgroup_per_node *pn, --=20 2.20.1