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b=WONIsc1lDroD/0B2DmWkU07c304Bgbaz1sDLm4sqC90nX5zNNUlehXG+d/k6WMGCL n1XsU5A4867Yp8O91JLHBXxmirPFn8fnK8bc+q2yicnGX/3eq1cMGZSFR74B+ljsvY 9PqGCRnW7WvIn8rAG2XkC9w8zfqBby7axEFF3CLbFM4G0RSNW0ZLv2h87dC29Ov8H1 KVSXwlkiOP+ujCOPheBlJv2Es9jtsDFXmanMKq5ryebUtMJk6R80sZLgZX5F5/LZqY VSlQ5nL6eatb8ZvlOCPuwZkme1LE+LjkYNEyatKLbMGGt2JpCEg3Jo1dIjmoyrJsBG 1F/u8KGuq8+rw== Date: Mon, 23 Mar 2026 21:25:25 +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: <2d39ea5e-fd69-4acf-8518-a504f5f7a838@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2d39ea5e-fd69-4acf-8518-a504f5f7a838@linux.dev> X-Rspam-User: X-Rspamd-Queue-Id: 2E26E100005 X-Rspamd-Server: rspam08 X-Stat-Signature: y7nthjrkikqs3sjzf5z8n3gc7c1dii61 X-HE-Tag: 1774268728-388669 X-HE-Meta: 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 x1256zZO FA1HvTDVS3NpVFjqXyRz9NFEfm/3Gm9jnO9xhx/TJR77/GlNUFtVHvK8xDFAVu47qZYiUo1N3raHWzxl2qe1XEWEHOpECoNmwXG8oZ0FsyfN7T1ysYw9URODp1FpcCN6+2MAjHBfILHdMoShJtxV7bSqlsnTHn8qcDLHZzG7zxnUyzywCcK4BV9VAHJAlxbsphFzFDjFNWIIv7T6E4RY0xhieodiffQdgkhrCgMxMzzbBtVzh5GKkrq7Jx+R5st1G0VM42eQWoSTt5Jomr1N0j722xKDOhj3LeFatfP7BY8FRMZI= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Mar 23, 2026 at 05:47:27PM +0800, Qi Zheng wrote: > Hi Harry, > > On 3/23/26 3:53 PM, Harry Yoo (Oracle) wrote: > > 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? > > The parameter and return value of memcg_state_val_in_pages() are both > of type int, so perhaps we need a cleanup patch to do this? Yes! and @val in memcg_rstat_updated() too, I think. > I will send a cleanup patchset to do this, which includes the following: > > https://lore.kernel.org/all/5e178b4e-a9e0-44dc-a18d-8c014365ee2f@linux.dev/ Thanks! Should that ideally be applied before this patchset? -- Cheers, Harry / Hyeonggon