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[109.81.29.60]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-499820f5d26sm32668385e9.1.2026.08.13.01.25.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 13 Aug 2026 01:25:48 -0700 (PDT) Date: Thu, 13 Aug 2026 10:25:47 +0200 From: Michal Hocko To: Shakeel Butt Cc: Andrew Morton , Johannes Weiner , Roman Gushchin , Muchun Song , David Hildenbrand , Lorenzo Stoakes , Kairui Song , Qi Zheng , Barry Song , Axel Rasmussen , Meta kernel team , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 5/9] memcg: remove the soft limit rbtree Message-ID: References: <20260811203203.3456029-1-shakeel.butt@linux.dev> <20260811203203.3456029-6-shakeel.butt@linux.dev> 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-Disposition: inline In-Reply-To: <20260811203203.3456029-6-shakeel.butt@linux.dev> On Tue 11-08-26 13:31:59, Shakeel Butt wrote: > With soft limit reclaim gone, the per-node rbtree of cgroups in excess > has no readers left. Remove the tree, the helpers maintaining it, and > the subsys_initcall that existed only to allocate it. memcg1_check_events() > no longer needs to feed it, which also drops the last caller of > lru_gen_soft_reclaim(). > > Signed-off-by: Shakeel Butt Acked-by: Michal Hocko Thanks! > --- > mm/memcontrol-v1.c | 176 +-------------------------------------------- > mm/memcontrol-v1.h | 2 - > mm/memcontrol.c | 1 - > 3 files changed, 2 insertions(+), 177 deletions(-) > > diff --git a/mm/memcontrol-v1.c b/mm/memcontrol-v1.c > index b38b8d0f7f51..475f998b7643 100644 > --- a/mm/memcontrol-v1.c > +++ b/mm/memcontrol-v1.c > @@ -17,23 +17,6 @@ > #include "swap_table.h" > #include "memcontrol-v1.h" > > -/* > - * Cgroups above their limits are maintained in a RB-Tree, independent of > - * their hierarchy representation > - */ > - > -struct mem_cgroup_tree_per_node { > - struct rb_root rb_root; > - struct rb_node *rb_rightmost; > - spinlock_t lock; > -}; > - > -struct mem_cgroup_tree { > - struct mem_cgroup_tree_per_node *rb_tree_per_node[MAX_NUMNODES]; > -}; > - > -static struct mem_cgroup_tree soft_limit_tree __read_mostly; > - > /* for OOM */ > struct mem_cgroup_eventfd_list { > struct list_head list; > @@ -99,133 +82,6 @@ static struct lockdep_map memcg_oom_lock_dep_map = { > > DEFINE_SPINLOCK(memcg_oom_lock); > > -static void __mem_cgroup_insert_exceeded(struct mem_cgroup_per_node *mz, > - struct mem_cgroup_tree_per_node *mctz, > - unsigned long new_usage_in_excess) > -{ > - struct rb_node **p = &mctz->rb_root.rb_node; > - struct rb_node *parent = NULL; > - struct mem_cgroup_per_node *mz_node; > - bool rightmost = true; > - > - if (mz->on_tree) > - return; > - > - mz->usage_in_excess = new_usage_in_excess; > - if (!mz->usage_in_excess) > - return; > - while (*p) { > - parent = *p; > - mz_node = rb_entry(parent, struct mem_cgroup_per_node, > - tree_node); > - if (mz->usage_in_excess < mz_node->usage_in_excess) { > - p = &(*p)->rb_left; > - rightmost = false; > - } else { > - p = &(*p)->rb_right; > - } > - } > - > - if (rightmost) > - mctz->rb_rightmost = &mz->tree_node; > - > - rb_link_node(&mz->tree_node, parent, p); > - rb_insert_color(&mz->tree_node, &mctz->rb_root); > - mz->on_tree = true; > -} > - > -static void __mem_cgroup_remove_exceeded(struct mem_cgroup_per_node *mz, > - struct mem_cgroup_tree_per_node *mctz) > -{ > - if (!mz->on_tree) > - return; > - > - if (&mz->tree_node == mctz->rb_rightmost) > - mctz->rb_rightmost = rb_prev(&mz->tree_node); > - > - rb_erase(&mz->tree_node, &mctz->rb_root); > - mz->on_tree = false; > -} > - > -static void mem_cgroup_remove_exceeded(struct mem_cgroup_per_node *mz, > - struct mem_cgroup_tree_per_node *mctz) > -{ > - unsigned long flags; > - > - spin_lock_irqsave(&mctz->lock, flags); > - __mem_cgroup_remove_exceeded(mz, mctz); > - spin_unlock_irqrestore(&mctz->lock, flags); > -} > - > -static unsigned long soft_limit_excess(struct mem_cgroup *memcg) > -{ > - unsigned long nr_pages = page_counter_read(&memcg->memory); > - unsigned long soft_limit = READ_ONCE(memcg->soft_limit); > - unsigned long excess = 0; > - > - if (nr_pages > soft_limit) > - excess = nr_pages - soft_limit; > - > - return excess; > -} > - > -static void memcg1_update_tree(struct mem_cgroup *memcg, int nid) > -{ > - unsigned long excess; > - struct mem_cgroup_per_node *mz; > - struct mem_cgroup_tree_per_node *mctz; > - > - if (lru_gen_enabled()) { > - if (soft_limit_excess(memcg)) > - lru_gen_soft_reclaim(memcg, nid); > - return; > - } > - > - mctz = soft_limit_tree.rb_tree_per_node[nid]; > - if (!mctz) > - return; > - /* > - * Necessary to update all ancestors when hierarchy is used. > - * because their event counter is not touched. > - */ > - for (; memcg; memcg = parent_mem_cgroup(memcg)) { > - mz = memcg->nodeinfo[nid]; > - excess = soft_limit_excess(memcg); > - /* > - * We have to update the tree if mz is on RB-tree or > - * mem is over its softlimit. > - */ > - if (excess || mz->on_tree) { > - unsigned long flags; > - > - spin_lock_irqsave(&mctz->lock, flags); > - /* if on-tree, remove it */ > - if (mz->on_tree) > - __mem_cgroup_remove_exceeded(mz, mctz); > - /* > - * Insert again. mz->usage_in_excess will be updated. > - * If excess is 0, no tree ops. > - */ > - __mem_cgroup_insert_exceeded(mz, mctz, excess); > - spin_unlock_irqrestore(&mctz->lock, flags); > - } > - } > -} > - > -void memcg1_remove_from_trees(struct mem_cgroup *memcg) > -{ > - struct mem_cgroup_tree_per_node *mctz; > - struct mem_cgroup_per_node *mz; > - int nid; > - > - for_each_node(nid) { > - mz = memcg->nodeinfo[nid]; > - mctz = soft_limit_tree.rb_tree_per_node[nid]; > - if (mctz) > - mem_cgroup_remove_exceeded(mz, mctz); > - } > -} > - > static u64 mem_cgroup_move_charge_read(struct cgroup_subsys_state *css, > struct cftype *cft) > { > @@ -336,7 +192,7 @@ static void mem_cgroup_threshold(struct mem_cgroup *memcg) > } > } > > -/* Cgroup1: threshold notifications & softlimit tree updates */ > +/* Cgroup1: threshold notifications */ > > /* > * Per memcg event counter is incremented at every pagein/pageout. With THP, > @@ -405,17 +261,8 @@ static void memcg1_check_events(struct mem_cgroup *memcg, int nid) > if (IS_ENABLED(CONFIG_PREEMPT_RT)) > return; > > - /* threshold event is triggered in finer grain than soft limit */ > - if (unlikely(memcg1_event_ratelimit(memcg, > - MEM_CGROUP_TARGET_THRESH))) { > - bool do_softlimit; > - > - do_softlimit = memcg1_event_ratelimit(memcg, > - MEM_CGROUP_TARGET_SOFTLIMIT); > + if (unlikely(memcg1_event_ratelimit(memcg, MEM_CGROUP_TARGET_THRESH))) > mem_cgroup_threshold(memcg); > - if (unlikely(do_softlimit)) > - memcg1_update_tree(memcg, nid); > - } > } > > void memcg1_commit_charge(struct folio *folio, struct mem_cgroup *memcg) > @@ -2391,22 +2238,3 @@ void memcg1_free_events(struct mem_cgroup *memcg) > { > free_percpu(memcg->events_percpu); > } > - > -static int __init memcg1_init(void) > -{ > - int node; > - > - for_each_node(node) { > - struct mem_cgroup_tree_per_node *rtpn; > - > - rtpn = kzalloc_node(sizeof(*rtpn), GFP_KERNEL, node); > - > - rtpn->rb_root = RB_ROOT; > - rtpn->rb_rightmost = NULL; > - spin_lock_init(&rtpn->lock); > - soft_limit_tree.rb_tree_per_node[node] = rtpn; > - } > - > - return 0; > -} > -subsys_initcall(memcg1_init); > diff --git a/mm/memcontrol-v1.h b/mm/memcontrol-v1.h > index 1e394269c613..fd611e66859a 100644 > --- a/mm/memcontrol-v1.h > +++ b/mm/memcontrol-v1.h > @@ -41,7 +41,6 @@ bool memcg1_alloc_events(struct mem_cgroup *memcg); > void memcg1_free_events(struct mem_cgroup *memcg); > > void memcg1_memcg_init(struct mem_cgroup *memcg); > -void memcg1_remove_from_trees(struct mem_cgroup *memcg); > > static inline void memcg1_soft_limit_reset(struct mem_cgroup *memcg) > { > @@ -98,7 +97,6 @@ static inline bool memcg1_alloc_events(struct mem_cgroup *memcg) { return true; > static inline void memcg1_free_events(struct mem_cgroup *memcg) {} > > static inline void memcg1_memcg_init(struct mem_cgroup *memcg) {} > -static inline void memcg1_remove_from_trees(struct mem_cgroup *memcg) {} > static inline void memcg1_soft_limit_reset(struct mem_cgroup *memcg) {} > static inline void memcg1_css_offline(struct mem_cgroup *memcg) {} > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 1d3339520809..b68f1f16ae54 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -4394,7 +4394,6 @@ static void mem_cgroup_css_free(struct cgroup_subsys_state *css) > > vmpressure_cleanup(&memcg->vmpressure); > cancel_work_sync(&memcg->high_work); > - memcg1_remove_from_trees(memcg); > free_shrinker_info(memcg); > mem_cgroup_free(memcg); > } > -- > 2.53.0-Meta -- Michal Hocko SUSE Labs