From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-177.mta0.migadu.com (out-177.mta0.migadu.com [91.218.175.177]) (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 10D3832E73E for ; Tue, 10 Feb 2026 06:48:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.177 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770706141; cv=none; b=QUh8Y4DoXeSjPH+q4oJYK/B1cvVkZoOg/j8+ZlEy9o2ex1dY9prseTpiocmoJ/TkDriKXA/8bpVMU+L78i+8YzPBtuoFVpNZolG+FAjR8j2YS4NerSYnLOmk8UrsAdLbqrx5MWAZEoBmjvSJL5eZj1RZWGV1P6/UawwKHMwWwSc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770706141; c=relaxed/simple; bh=av8q2nJWKq8RrTg/WR50IKQK3VHKFzKGZobwrbgdZ10=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=dmKgL+i6fOqfA6KOQPp4FrGFPH5OPSasS89u4jwkRoNfnRxiysb4E70E6YIjw8sXTc38H7S9m+V7r93nG1GvtoqPAm/Jj1Rl9lqWc1kBGxUr4V5HZoBA/YqKdwgJZUkkvxX/u+ek5XwLHHH3cUTo4GT8z/E46fvlsPnauf8I0L4= 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=SSaMr9CM; arc=none smtp.client-ip=91.218.175.177 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="SSaMr9CM" Message-ID: <0673b72c-8d7c-4bfb-a8b2-da5ae5bb5f00@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1770706134; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=gci4PxuqdlVZBIC34roKwVj2Mfy+C8h8ARtkl3i8WIY=; b=SSaMr9CM00eCMtfnra8fKpSRNM1+c0aPKMj1MD0cAoZblfvnkKQXyvcqoR81FqlGV0N4Xx pxfCEDp4XVBfyLkFJD9DX+O9svXp/lTZ2WWei+cAMbVC4zB6+t1YLRR3zPETzg+39VRM8B Kls1/747RlPwiw9yujsPbGNpwi60j48= Date: Tue, 10 Feb 2026 14:47:51 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v4 29/31] mm: memcontrol: prepare for reparenting non-hierarchical stats To: Shakeel Butt Cc: hannes@cmpxchg.org, hughd@google.com, mhocko@suse.com, roman.gushchin@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, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Qi Zheng References: <3ca234c643ecb484f17aa88187e0bce8949bdb6b.1770279888.git.zhengqi.arch@bytedance.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Qi Zheng In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 2/7/26 10:19 AM, Shakeel Butt wrote: > On Thu, Feb 05, 2026 at 05:01:48PM +0800, Qi Zheng wrote: >> 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 > > Overall looks good just a couple of comments. > >> --- >> 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, >> >> 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); > > Put the above in mm/memcontrol-v1.h file. OK. > >> 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); > > Put the above in mm/memcontrol-v1.h file. OK. > >> >> 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 = >> - container_of(work, struct cgroup_subsys_state, destroy_work); >> + struct cgroup_subsys_state *css = container_of(to_rcu_work(work), >> + struct cgroup_subsys_state, destroy_rwork); >> >> cgroup_lock(); >> >> @@ -6065,8 +6065,8 @@ 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 c6078cd7f7e53..a427bb205763b 100644 >> --- a/mm/memcontrol-v1.c >> +++ b/mm/memcontrol-v1.c >> @@ -1887,6 +1887,22 @@ 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 eb3c3c1056574..45528195d3578 100644 >> --- a/mm/memcontrol-v1.h >> +++ b/mm/memcontrol-v1.h >> @@ -41,6 +41,7 @@ static inline bool do_memsw_account(void) >> >> 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, unsigned 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, 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 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_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; >> + >> + __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); >> +} >> +#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); >> @@ -407,7 +427,7 @@ struct lruvec_stats { >> long state[NR_MEMCG_NODE_STAT_ITEMS]; >> >> /* Non-hierarchical (CPU aggregated) state */ >> - long state_local[NR_MEMCG_NODE_STAT_ITEMS]; >> + atomic_long_t state_local[NR_MEMCG_NODE_STAT_ITEMS]; >> >> /* 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 *lruvec, >> return 0; >> >> pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec); >> - x = READ_ONCE(pn->lruvec_stats->state_local[i]); >> + x = atomic_long_read(&(pn->lruvec_stats->state_local[i])); >> #ifdef CONFIG_SMP >> if (x < 0) >> x = 0; >> @@ -458,6 +478,27 @@ unsigned long lruvec_page_state_local(struct lruvec *lruvec, >> return x; >> } >> > > Please put the following function under CONFIG_MEMCG_V1. Just move it in > the same block as reparent_state_local(). OK, will try to do it. > >> +void reparent_memcg_lruvec_state_local(struct mem_cgroup *memcg, >> + struct mem_cgroup *parent, int idx) >> +{ >> + int i = memcg_stats_index(idx); >> + int nid; >> + >> + if (WARN_ONCE(BAD_STAT_IDX(i), "%s: missing stat item %d\n", __func__, idx)) >> + return; >> + >> + 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)); >> + struct mem_cgroup_per_node *parent_pn; >> + unsigned long value = lruvec_page_state_local(child_lruvec, idx); >> + >> + parent_pn = container_of(parent_lruvec, struct mem_cgroup_per_node, lruvec); >> + >> + atomic_long_add(value, &(parent_pn->lruvec_stats->state_local[i])); >> + } >> +} >> + > > [...] > >> >> +#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 > > Add the usage of these start and end functions in mod_memcg_state() and > mod_memcg_lruvec_state() in this patch. Using these two function will change the behavior of mod_memcg_state() and mod_memcg_lruvec_state(), but LRU folios has not yet been reparented. To ensure the patch itself is error-free, I chose to place the usage of these two function in patch #30. Thanks, Qi >