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Date:   Mon, 12 Apr 2021 11:04:23 -0700
From:   Roman Gushchin <guro@fb.com>
To:     Waiman Long <longman@redhat.com>
CC:     Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Tejun Heo <tj@kernel.org>, Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        <linux-kernel@vger.kernel.org>, <cgroups@vger.kernel.org>,
        <linux-mm@kvack.org>, Shakeel Butt <shakeelb@google.com>,
        Muchun Song <songmuchun@bytedance.com>,
        Alex Shi <alex.shi@linux.alibaba.com>,
        Chris Down <chris@chrisdown.name>,
        Yafang Shao <laoar.shao@gmail.com>,
        Alexander Duyck <alexander.h.duyck@linux.intel.com>,
        Wei Yang <richard.weiyang@gmail.com>,
        Masayoshi Mizuma <msys.mizuma@gmail.com>
Subject: Re: [PATCH 1/5] mm/memcg: Pass both memcg and lruvec to
 mod_memcg_lruvec_state()
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References: <20210409231842.8840-1-longman@redhat.com>
 <20210409231842.8840-2-longman@redhat.com>
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On Fri, Apr 09, 2021 at 07:18:38PM -0400, Waiman Long wrote:
> The caller of mod_memcg_lruvec_state() has both memcg and lruvec readily
> available. So both of them are now passed to mod_memcg_lruvec_state()
> and __mod_memcg_lruvec_state(). The __mod_memcg_lruvec_state() is
> updated to allow either of the two parameters to be set to null. This
> makes mod_memcg_lruvec_state() equivalent to mod_memcg_state() if lruvec
> is null.

This patch seems to be correct, but it's a bit hard to understand why
it's required without looking into the rest of the series. Can you, please,
add a couple of words about it? E.g. we need it to handle stats which do not
exist on the lruvec level...

Otherwise,
Acked-by: Roman Gushchin <guro@fb.com>

Thanks!

> 
> Signed-off-by: Waiman Long <longman@redhat.com>
> ---
>  include/linux/memcontrol.h | 12 +++++++-----
>  mm/memcontrol.c            | 19 +++++++++++++------
>  mm/slab.h                  |  2 +-
>  3 files changed, 21 insertions(+), 12 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 0c04d39a7967..95f12996e66c 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -955,8 +955,8 @@ static inline unsigned long lruvec_page_state_local(struct lruvec *lruvec,
>  	return x;
>  }
>  
> -void __mod_memcg_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx,
> -			      int val);
> +void __mod_memcg_lruvec_state(struct mem_cgroup *memcg, struct lruvec *lruvec,
> +			      enum node_stat_item idx, int val);
>  void __mod_lruvec_kmem_state(void *p, enum node_stat_item idx, int val);
>  
>  static inline void mod_lruvec_kmem_state(void *p, enum node_stat_item idx,
> @@ -969,13 +969,14 @@ static inline void mod_lruvec_kmem_state(void *p, enum node_stat_item idx,
>  	local_irq_restore(flags);
>  }
>  
> -static inline void mod_memcg_lruvec_state(struct lruvec *lruvec,
> +static inline void mod_memcg_lruvec_state(struct mem_cgroup *memcg,
> +					  struct lruvec *lruvec,
>  					  enum node_stat_item idx, int val)
>  {
>  	unsigned long flags;
>  
>  	local_irq_save(flags);
> -	__mod_memcg_lruvec_state(lruvec, idx, val);
> +	__mod_memcg_lruvec_state(memcg, lruvec, idx, val);
>  	local_irq_restore(flags);
>  }
>  
> @@ -1369,7 +1370,8 @@ static inline unsigned long lruvec_page_state_local(struct lruvec *lruvec,
>  	return node_page_state(lruvec_pgdat(lruvec), idx);
>  }
>  
> -static inline void __mod_memcg_lruvec_state(struct lruvec *lruvec,
> +static inline void __mod_memcg_lruvec_state(struct mem_cgroup *memcg,
> +					    struct lruvec *lruvec,
>  					    enum node_stat_item idx, int val)
>  {
>  }
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index e064ac0d850a..d66e1e38f8ac 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -799,20 +799,27 @@ parent_nodeinfo(struct mem_cgroup_per_node *pn, int nid)
>  	return mem_cgroup_nodeinfo(parent, nid);
>  }
>  
> -void __mod_memcg_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx,
> -			      int val)
> +/*
> + * Either one of memcg or lruvec can be NULL, but not both.
> + */
> +void __mod_memcg_lruvec_state(struct mem_cgroup *memcg, struct lruvec *lruvec,
> +			      enum node_stat_item idx, int val)
>  {
>  	struct mem_cgroup_per_node *pn;
> -	struct mem_cgroup *memcg;
>  	long x, threshold = MEMCG_CHARGE_BATCH;
>  
> +	/* Update lruvec */
>  	pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
> -	memcg = pn->memcg;
> +
> +	if (!memcg)
> +		memcg = pn->memcg;
>  
>  	/* Update memcg */
>  	__mod_memcg_state(memcg, idx, val);
>  
> -	/* Update lruvec */
> +	if (!lruvec)
> +		return;
> +
>  	__this_cpu_add(pn->lruvec_stat_local->count[idx], val);
>  
>  	if (vmstat_item_in_bytes(idx))
> @@ -848,7 +855,7 @@ void __mod_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx,
>  
>  	/* Update memcg and lruvec */
>  	if (!mem_cgroup_disabled())
> -		__mod_memcg_lruvec_state(lruvec, idx, val);
> +		__mod_memcg_lruvec_state(NULL, lruvec, idx, val);
>  }
>  
>  void __mod_lruvec_page_state(struct page *page, enum node_stat_item idx,
> diff --git a/mm/slab.h b/mm/slab.h
> index 076582f58f68..bc6c7545e487 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -293,7 +293,7 @@ static inline void mod_objcg_state(struct obj_cgroup *objcg,
>  	rcu_read_lock();
>  	memcg = obj_cgroup_memcg(objcg);
>  	lruvec = mem_cgroup_lruvec(memcg, pgdat);
> -	mod_memcg_lruvec_state(lruvec, idx, nr);
> +	mod_memcg_lruvec_state(memcg, lruvec, idx, nr);
>  	rcu_read_unlock();
>  }
>  
> -- 
> 2.18.1
>