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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 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: A90F1100003 X-Stat-Signature: e3yx558rkjd5ajhqsm3ipo5ht78e7w33 X-Rspam-User: X-HE-Tag: 1772418628-487195 X-HE-Meta: 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 HAab9ZkW bF5AFinD0Ti1DZ2lCDiCbzLRox8liwOI2BtROfWKgXXPsammPx/lDgCvYYx69TEpYBaGtCKjL5xmaq0j+Cxxim06j3TlOHRGtZrLUfYfD3x437S21XoNkzxk+JwbDQOgce00IHWcqz6uJW7onDEL6pDwR/72rPrVqXPaLwysq79eeeO/x1fS+NgtGuMVEyX2Dr7DSCQxjP3rtvtlXP+tV6ZEoWg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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); > _ >