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From: Qi Zheng In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 9FC2D40008 X-Stat-Signature: jr6gbo9ztx3f9wsp6a4i1dkuudw7h5uj X-HE-Tag: 1774320904-242650 X-HE-Meta: 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 rOM2cANU zfHgyk0BK5npORNpQwv6+21JpCSs2fLQ+6/iKQ/CNDc0FimewIvpTaN2m2s2dhKyXMSEt2Z1nnf+eadGl7CvkpA6dgXVOUCDM9ZWNJmC11aNAU7FR5X21GZVDPwBDlypfiIxzywdpU4Yys1Nx4lgD3a9LykwIiYuUDu+bd950tmF5RZMPhGS8Gr5hqj60YCZ4xgHo+iFvamiV02ct7iOF/kbFxEbWJfuPNF7YXG1jcGlMDbB2Rgmvntl7asJQQUQXfrR+ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/23/26 8:25 PM, Harry Yoo (Oracle) wrote: > 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. Right. > >> 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? This would conflict with the current patchset. The v6 has been in mm-unstable for some time, so I prefer to add a cleanup patchset to avoid interfering with the merge of this patchset. Otherwise, sending v7 might be more appropriate. Thanks, Qi >