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

[Alexandre Ghiti]

On 5/21/26 19:28, Shakeel Butt wrote:
> 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@xxxxxxxx>
> > ---
> >   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?


Sashiko raised the same question, so I need to be educated here: what 
currently guarantees the life objcg returned by current_obj_cgroup()?


>