From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-180.mta0.migadu.com (out-180.mta0.migadu.com [91.218.175.180]) (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 2D117430B86 for ; Mon, 2 Mar 2026 02:30:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.180 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772418632; cv=none; b=I5/WSSC0b310S1a4bH75un/SG5lXv48363CdNkuKMyfd5ZFjgNCkgL26GqFA7uBR4ebJwb+KiY73PrXpKSuEAEV74Dyy7JscN5XlVpyveO9Jqbu+YiiYJ1kFzKjAoUoFL6jNwJuQIk43nJVqPUFmUKy2jSkhsUmBpWJgESK9joE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772418632; c=relaxed/simple; bh=03kwRSZnZOSxHYms+OZE6egQdOddDSI4/mOREuNMCGs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=YiPR0hIIMeSJ93arR9vODeOEDCSfSD1Nfy3TbxpOs3OBKtTf4MK6K0jax4puomdNUPnK7izK57ILGYbq16r+pOoesag/7xv+69uau+gSqJ+WE7WhX6D6bfv+NRdame57+nko6hQ3Zm0IF5hVw/8zm4arZAKQ74j7TO8im16fxfU= 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=Oy5lfPc3; arc=none smtp.client-ip=91.218.175.180 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="Oy5lfPc3" Message-ID: <953e1e1d-1c76-4703-8d22-5b060d5e5832@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1772418626; 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=CZmVkvEA0MEnZ8U+s7EY+/k40UTfgu8GKtx0XwLwjrA=; b=Oy5lfPc3zRop4/4ghKao1ZS7ddX7Oskv61dxkNI/s8vhiy+cWdLgCcLOqawPbV/DcqKrdv EmJwfvd1XKVJVcykhHNeUYYCNAFGFP992+87AgbCgGkUcGVIKj4CUTz8MZTv36p1GDbnpg CF7dVnqh4gFkgcheIajmEBx7d7rSzf0= Date: Mon, 2 Mar 2026 10:30:05 +0800 Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v5 update 29/32] mm: memcontrol: prepare for reparenting non-hierarchical stats To: Andrew Morton 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 References: <20260228072556.31793-1-qi.zheng@linux.dev> <20260228110800.50bfca2a90912142c11e2922@linux-foundation.org> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Qi Zheng In-Reply-To: <20260228110800.50bfca2a90912142c11e2922@linux-foundation.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT Hi Andrew, On 3/1/26 3:08 AM, Andrew Morton wrote: > 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? Oh sorry, I forgot the changlog. > > 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 Based on Yosry Ahmed's suggestion and diff, the method has been changed to non-atomic mode, so there is no need to test the perfomance impact of atomic mode. > https://lkml.kernel.org/r/aZ-kefGBeT-RzGcG@linux.dev This redundant declaration has been removed. Thanks, Qi > > 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); > _ >