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b=NoUOiYcwo/H7w+dsYAyFCvOVNzzuboDFucLEAGhVJsh7zhirN/JAuNuWb0IChI9YA 9vacG2nDCrg4TOJCH796WyyHEbOdUj3Aa+3UtJY1Dfadu4cwp7rNVm3Sm7lQiFtaip jMomh59jceywvp/GIcqbU0lzcwFWAN1r/xkmxSD7p/xu7/U4U3WkKGImyP7YS7t9NH R4jDo3sditHBH6CeIMfspKwqM2K8ekpeVDT6WOasAdfhcDqeQ0MQmD0j4BDk5p4+1G 4kXhH2gwBcnwv0DFDxUPMmYMGdOUpmSvIENx8GDttcQfl6Z68qPMvt8k4kpdZy5Ntr C5f2nbGbZY1dw== Date: Mon, 23 Mar 2026 16:53:12 +0900 From: "Harry Yoo (Oracle)" 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, akpm@linux-foundation.org, 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 v6 30/33] mm: memcontrol: prepare for reparenting non-hierarchical stats Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: 19cudwcgycr1u1euu8y3kkiaydafjkin X-Rspamd-Server: rspam09 X-Rspam-User: X-Rspamd-Queue-Id: B11FC4000B X-HE-Tag: 1774252395-254946 X-HE-Meta: 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 EGVFpfdy 3d5g1D4KbeCh0zqF8krLELE/LuJH7nnwt40np+yeK98djvFXQrBLYyCe4QR3k+SrVZv+vetPGI5FjTyyg/SXY8nq9Rnbpj+H3NGfeTc92yXtdpcWRx6p51tWctbxFHZNKWpRxv8ljmagcs325bwXmHC0FEmVSELS0vVwkKEuHow8qx00dpKUtqKkZoRTVlXzjbRcxABB3TrEEHX7nv2EbX4FwoOyx1/0mz0OsAVl+DSrAovrnErb6ax3ZdKf+Cv1r06/GjflGcuaTzx+sqOYvzTPoZDhpYX0I5Iz0dCAoOUOfVaU= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Mar 05, 2026 at 07:52:48PM +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() > > Co-developed-by: Yosry Ahmed > Signed-off-by: Yosry Ahmed > Signed-off-by: Qi Zheng > Acked-by: Shakeel Butt > --- > kernel/cgroup/cgroup.c | 9 ++-- > mm/memcontrol-v1.c | 16 +++++++ > mm/memcontrol-v1.h | 7 +++ > mm/memcontrol.c | 97 ++++++++++++++++++++++++++++++++++++++++++ > 4 files changed, 125 insertions(+), 4 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 23b70bd80ddc9..b0519a16f5684 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -473,6 +501,30 @@ unsigned long lruvec_page_state_local(struct lruvec *lruvec, > return x; > } > > +#ifdef CONFIG_MEMCG_V1 > +static void __mod_memcg_lruvec_state(struct mem_cgroup_per_node *pn, > + enum node_stat_item idx, int val); > + > +void reparent_memcg_lruvec_state_local(struct mem_cgroup *memcg, > + struct mem_cgroup *parent, int idx) > +{ > + int nid; > + > + 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)); > + unsigned long value = lruvec_page_state_local(child_lruvec, idx); > + struct mem_cgroup_per_node *child_pn, *parent_pn; > + > + child_pn = container_of(child_lruvec, struct mem_cgroup_per_node, lruvec); > + parent_pn = container_of(parent_lruvec, struct mem_cgroup_per_node, lruvec); > + > + __mod_memcg_lruvec_state(child_pn, idx, -value); > + __mod_memcg_lruvec_state(parent_pn, idx, value); We should probably change the type of `@val` from int to val to avoid losing non hierarchical stats during reparenting? > #ifdef CONFIG_MEMCG_V1 > static void __mod_memcg_state(struct mem_cgroup *memcg, > enum memcg_stat_item idx, int val) > > @@ -769,6 +857,15 @@ unsigned long memcg_page_state_local(struct mem_cgroup *memcg, int idx) > #endif > return x; > } > + > +void reparent_memcg_state_local(struct mem_cgroup *memcg, > + struct mem_cgroup *parent, int idx) > +{ > + unsigned long value = memcg_page_state_local(memcg, idx); > + > + __mod_memcg_state(memcg, idx, -value); > + __mod_memcg_state(parent, idx, value); > +} Same here. Otherwise LGTM. > #endif > > static void __mod_memcg_lruvec_state(struct mem_cgroup_per_node *pn, -- Cheers, Harry / Hyeonggon