From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 6DD3E3E7158; Sat, 28 Feb 2026 19:08:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772305682; cv=none; b=sFQDZCjXLgp5KBqaqtxh/d7gP2gSAPsapAG1k3ybqci+zhlZR9GG52HGrb7bcqN42vyYvgE7w320HmEzQLQS0EjjkZQF5ZPQ5KdeEDwNdUmdFqtDp6YQMPlfMIw/Ru9rSDoekuajwI+qnW3NmmTRAIcghFddFEJ9MfyTt2zUrwE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772305682; c=relaxed/simple; bh=ECFj6PIlpgHGhqNluMLaNy+SmRjHOXDaaWlrfELFWo0=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=E0xDn3aisxB9l0a6ZlEOIar3CFIwQN81asQro/tDaKE2b1FyAp5z2bR6yJZqzx4VAdzwgTVG0BnaU268sih32s4PFBECfVEXmx9yykdFWpWkNy/TBN1E+E188138MyqxPBR3fDeIDBsHw+BsC0DhSsRETbKpAzyJSlfFa0ggS7I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=yfql9eeJ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="yfql9eeJ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2702FC116D0; Sat, 28 Feb 2026 19:08:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1772305682; bh=ECFj6PIlpgHGhqNluMLaNy+SmRjHOXDaaWlrfELFWo0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=yfql9eeJU+5rH9cNSzrzpm/RDZf7mTiaCCY25VcG+3U0s9O2PQ5HPfwAl8tKdillT VDaJjVMqrk6F5sF7EKI/xo+I9pi6J89yETNqcyg64igqrmsRoBIpbxAhwj58eVG8Q3 Cs66D+FaBMq7EiWWU36EFJXdEU1+PNSH//muc41A= Date: Sat, 28 Feb 2026 11:08:00 -0800 From: Andrew Morton To: Qi Zheng Cc: 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, hamzamahfooz@linux.microsoft.com, apais@linux.microsoft.com, lance.yang@linux.dev, bhe@redhat.com, usamaarif642@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Qi Zheng , Yosry Ahmed Subject: Re: [PATCH v5 update 29/32] mm: memcontrol: prepare for reparenting non-hierarchical stats Message-Id: <20260228110800.50bfca2a90912142c11e2922@linux-foundation.org> In-Reply-To: <20260228072556.31793-1-qi.zheng@linux.dev> References: <20260228072556.31793-1-qi.zheng@linux.dev> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Sat, 28 Feb 2026 15:25:56 +0800 Qi Zheng wrote: > 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() That's a big update (delta patch is below). What did it all do? I've bookmarked these reviewer comments: https://lkml.kernel.org/r/CAO9r8zOhZgrym6oSrtg7b+HmNHEfWuAzZ0i8eYhm5-OEnfFLdw@mail.gmail.com https://lkml.kernel.org/r/aZ-R87JfacQ2gGq1@linux.dev https://lkml.kernel.org/r/aZ-kefGBeT-RzGcG@linux.dev Were they all addressed in some fashion? include/linux/memcontrol.h | 1 mm/memcontrol-v1.h | 1 mm/memcontrol.c | 89 ++++++++++++++++++++++++++--------- 3 files changed, 68 insertions(+), 23 deletions(-) --- a/include/linux/memcontrol.h~mm-memcontrol-prepare-for-reparenting-non-hierarchical-stats-update +++ a/include/linux/memcontrol.h @@ -956,7 +956,6 @@ static inline void mod_memcg_page_state( unsigned long memcg_events(struct mem_cgroup *memcg, int event); unsigned long memcg_page_state(struct mem_cgroup *memcg, 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); --- a/mm/memcontrol.c~mm-memcontrol-prepare-for-reparenting-non-hierarchical-stats-update +++ a/mm/memcontrol.c @@ -234,11 +234,19 @@ static inline void reparent_state_local( 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) @@ -442,7 +450,7 @@ struct lruvec_stats { long state[NR_MEMCG_NODE_STAT_ITEMS]; /* Non-hierarchical (CPU aggregated) state */ - atomic_long_t state_local[NR_MEMCG_NODE_STAT_ITEMS]; + long state_local[NR_MEMCG_NODE_STAT_ITEMS]; /* Pending child counts during tree propagation */ long state_pending[NR_MEMCG_NODE_STAT_ITEMS]; @@ -485,7 +493,7 @@ unsigned long lruvec_page_state_local(st return 0; pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec); - x = atomic_long_read(&(pn->lruvec_stats->state_local[i])); + x = READ_ONCE(pn->lruvec_stats->state_local[i]); #ifdef CONFIG_SMP if (x < 0) x = 0; @@ -494,6 +502,9 @@ unsigned long lruvec_page_state_local(st } #ifdef CONFIG_MEMCG_V1 +static void __mod_memcg_lruvec_state(struct lruvec *lruvec, + enum node_stat_item idx, int val); + void reparent_memcg_lruvec_state_local(struct mem_cgroup *memcg, struct mem_cgroup *parent, int idx) { @@ -506,12 +517,10 @@ void reparent_memcg_lruvec_state_local(s 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])); + __mod_memcg_lruvec_state(child_lruvec, idx, -value); + __mod_memcg_lruvec_state(parent_lruvec, idx, value); } } #endif @@ -598,7 +607,7 @@ struct memcg_vmstats { unsigned long events[NR_MEMCG_EVENTS]; /* Non-hierarchical (CPU aggregated) page state & events */ - atomic_long_t state_local[MEMCG_VMSTAT_SIZE]; + long state_local[MEMCG_VMSTAT_SIZE]; unsigned long events_local[NR_MEMCG_EVENTS]; /* Pending child counts during tree propagation */ @@ -835,7 +844,7 @@ unsigned long memcg_page_state_local(str if (WARN_ONCE(BAD_STAT_IDX(i), "%s: missing stat item %d\n", __func__, idx)) return 0; - x = atomic_long_read(&(memcg->vmstats->state_local[i])); + x = READ_ONCE(memcg->vmstats->state_local[i]); #ifdef CONFIG_SMP if (x < 0) x = 0; @@ -843,6 +852,51 @@ unsigned long memcg_page_state_local(str return x; } +static void __mod_memcg_state(struct mem_cgroup *memcg, + enum memcg_stat_item idx, int val) +{ + int i = memcg_stats_index(idx); + int cpu; + + if (mem_cgroup_disabled()) + return; + + cpu = get_cpu(); + + this_cpu_add(memcg->vmstats_percpu->state[i], val); + val = memcg_state_val_in_pages(idx, val); + memcg_rstat_updated(memcg, val, cpu); + trace_mod_memcg_state(memcg, idx, val); + + put_cpu(); +} + +static void __mod_memcg_lruvec_state(struct lruvec *lruvec, + enum node_stat_item idx, int val) +{ + struct mem_cgroup_per_node *pn; + struct mem_cgroup *memcg; + int i = memcg_stats_index(idx); + int cpu; + + pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec); + memcg = pn->memcg; + + cpu = get_cpu(); + + /* Update memcg */ + this_cpu_add(memcg->vmstats_percpu->state[i], val); + + /* Update lruvec */ + this_cpu_add(pn->lruvec_stats_percpu->state[i], val); + + val = memcg_state_val_in_pages(idx, val); + memcg_rstat_updated(memcg, val, cpu); + trace_mod_memcg_lruvec_state(memcg, idx, val); + + put_cpu(); +} + void reparent_memcg_state_local(struct mem_cgroup *memcg, struct mem_cgroup *parent, int idx) { @@ -852,7 +906,8 @@ void reparent_memcg_state_local(struct m if (WARN_ONCE(BAD_STAT_IDX(i), "%s: missing stat item %d\n", __func__, idx)) return; - atomic_long_add(value, &(parent->vmstats->state_local[i])); + __mod_memcg_state(memcg, idx, -value); + __mod_memcg_state(parent, idx, value); } #endif @@ -4174,8 +4229,6 @@ 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 */ @@ -4213,12 +4266,8 @@ static void mem_cgroup_stat_aggregate(st } /* Aggregate counts on this level and propagate upwards */ - if (delta_cpu) { - if (ac->local) - ac->local[i] += delta_cpu; - else if (ac->alocal) - atomic_long_add(delta_cpu, &(ac->alocal[i])); - } + if (delta_cpu) + ac->local[i] += delta_cpu; if (delta) { ac->aggregate[i] += delta; @@ -4289,8 +4338,7 @@ static void mem_cgroup_css_rstat_flush(s ac = (struct aggregate_control) { .aggregate = memcg->vmstats->state, - .local = NULL, - .alocal = memcg->vmstats->state_local, + .local = memcg->vmstats->state_local, .pending = memcg->vmstats->state_pending, .ppending = parent ? parent->vmstats->state_pending : NULL, .cstat = statc->state, @@ -4323,8 +4371,7 @@ static void mem_cgroup_css_rstat_flush(s ac = (struct aggregate_control) { .aggregate = lstats->state, - .local = NULL, - .alocal = lstats->state_local, + .local = lstats->state_local, .pending = lstats->state_pending, .ppending = plstats ? plstats->state_pending : NULL, .cstat = lstatc->state, --- a/mm/memcontrol-v1.h~mm-memcontrol-prepare-for-reparenting-non-hierarchical-stats-update +++ a/mm/memcontrol-v1.h @@ -45,7 +45,6 @@ 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); _