Re: [PATCH 4/8] mm: memcontrol: track MEMCG_KMEM per NUMA node

[Shakeel Butt <shakeel.butt@linux.dev>]

On Mon, May 11, 2026 at 10:20:39PM +0200, Alexandre Ghiti wrote:
> This patch gets rid of MEMCG_KMEM and wires all the "generic" functions
> by introducing per-node obj_cgroup objects.
> 
> Note that it does not convert the kmem users to proper per-memcg-per-node
> accounting now, this is done in upcoming patches.
> 
> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
> ---
>  include/linux/memcontrol.h | 23 ++++++++++----
>  include/linux/mmzone.h     |  1 +
>  mm/memcontrol.c            | 64 ++++++++++++++++++++++++--------------
>  mm/vmstat.c                |  1 +
>  4 files changed, 59 insertions(+), 30 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 568ab08f42af..17cf823160e4 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -35,7 +35,6 @@ enum memcg_stat_item {
>  	MEMCG_SWAP = NR_VM_NODE_STAT_ITEMS,
>  	MEMCG_SOCK,
>  	MEMCG_PERCPU_B,
> -	MEMCG_KMEM,
>  	MEMCG_ZSWAP_B,
>  	MEMCG_ZSWAPPED,
>  	MEMCG_ZSWAP_INCOMP,
> @@ -126,9 +125,10 @@ struct mem_cgroup_per_node {
>  	struct list_head objcg_list;
>  
>  #ifdef CONFIG_MEMCG_NMI_SAFETY_REQUIRES_ATOMIC
> -	/* slab stats for nmi context */
> +	/* slab and kmem stats for nmi context */
>  	atomic_t		slab_reclaimable;
>  	atomic_t		slab_unreclaimable;
> +	atomic_t		kmem;
>  #endif
>  };
>  
> @@ -190,6 +190,7 @@ struct obj_cgroup {
>  		struct rcu_head rcu;
>  	};
>  	bool is_root;
> +	int nid;
>  };
>  
>  /*
> @@ -254,10 +255,6 @@ struct mem_cgroup {
>  	atomic_long_t		memory_events[MEMCG_NR_MEMORY_EVENTS];
>  	atomic_long_t		memory_events_local[MEMCG_NR_MEMORY_EVENTS];
>  
> -#ifdef CONFIG_MEMCG_NMI_SAFETY_REQUIRES_ATOMIC
> -	/* MEMCG_KMEM for nmi context */
> -	atomic_t		kmem_stat;
> -#endif
>  	/*
>  	 * Hint of reclaim pressure for socket memroy management. Note
>  	 * that this indicator should NOT be used in legacy cgroup mode
> @@ -776,6 +773,20 @@ static inline void obj_cgroup_put(struct obj_cgroup *objcg)
>  		percpu_ref_put(&objcg->refcnt);
>  }
>  
> +static inline struct obj_cgroup *obj_cgroup_get_nid(struct obj_cgroup *objcg,
> +						    int nid)
> +{
> +	struct obj_cgroup *nid_objcg;
> +	struct mem_cgroup *memcg;
> +
> +	rcu_read_lock();
> +	memcg = obj_cgroup_memcg(objcg);
> +	nid_objcg = rcu_dereference(memcg->nodeinfo[nid]->objcg);
> +	rcu_read_unlock();
> +
> +	return nid_objcg;

What is guarating the life of nid_objcg?