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Date:   Wed, 14 Apr 2021 11:44:10 +0200
From:   Michal Hocko <mhocko@suse.com>
To:     Muchun Song <songmuchun@bytedance.com>
Cc:     guro@fb.com, hannes@cmpxchg.org, akpm@linux-foundation.org,
        shakeelb@google.com, vdavydov.dev@gmail.com,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        duanxiongchun@bytedance.com, fam.zheng@bytedance.com
Subject: Re: [PATCH 4/7] mm: memcontrol: simplify lruvec_holds_page_lru_lock
Message-ID: <YHa5ao/JgoqHQh0Z@dhcp22.suse.cz>
References: <20210413065153.63431-1-songmuchun@bytedance.com>
 <20210413065153.63431-5-songmuchun@bytedance.com>
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In-Reply-To: <20210413065153.63431-5-songmuchun@bytedance.com>
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On Tue 13-04-21 14:51:50, Muchun Song wrote:
> We already have a helper lruvec_memcg() to get the memcg from lruvec, we
> do not need to do it ourselves in the lruvec_holds_page_lru_lock(). So use
> lruvec_memcg() instead. And if mem_cgroup_disabled() returns false, the
> page_memcg(page) (the LRU pages) cannot be NULL. So remove the odd logic
> of "memcg = page_memcg(page) ? : root_mem_cgroup". And use lruvec_pgdat
> to simplify the code. We can have a single definition for this function
> that works for !CONFIG_MEMCG, CONFIG_MEMCG + mem_cgroup_disabled() and
> CONFIG_MEMCG.

Neat. While you are at it wouldn't it make sesne to rename the function
as well. I do not want to bikeshed but this is really a misnomer. it
doesn't check anything about locking. page_belongs_lruvec?

> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  include/linux/memcontrol.h | 31 +++++++------------------------
>  1 file changed, 7 insertions(+), 24 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 4f49865c9958..38b8d3fb24ff 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -755,22 +755,6 @@ static inline struct lruvec *mem_cgroup_page_lruvec(struct page *page)
>  	return mem_cgroup_lruvec(memcg, pgdat);
>  }
>  
> -static inline bool lruvec_holds_page_lru_lock(struct page *page,
> -					      struct lruvec *lruvec)
> -{
> -	pg_data_t *pgdat = page_pgdat(page);
> -	const struct mem_cgroup *memcg;
> -	struct mem_cgroup_per_node *mz;
> -
> -	if (mem_cgroup_disabled())
> -		return lruvec == &pgdat->__lruvec;
> -
> -	mz = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
> -	memcg = page_memcg(page) ? : root_mem_cgroup;
> -
> -	return lruvec->pgdat == pgdat && mz->memcg == memcg;
> -}
> -
>  struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p);
>  
>  struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm);
> @@ -1229,14 +1213,6 @@ static inline struct lruvec *mem_cgroup_page_lruvec(struct page *page)
>  	return &pgdat->__lruvec;
>  }
>  
> -static inline bool lruvec_holds_page_lru_lock(struct page *page,
> -					      struct lruvec *lruvec)
> -{
> -	pg_data_t *pgdat = page_pgdat(page);
> -
> -	return lruvec == &pgdat->__lruvec;
> -}
> -
>  static inline void lruvec_memcg_debug(struct lruvec *lruvec, struct page *page)
>  {
>  }
> @@ -1518,6 +1494,13 @@ static inline void unlock_page_lruvec_irqrestore(struct lruvec *lruvec,
>  	spin_unlock_irqrestore(&lruvec->lru_lock, flags);
>  }
>  
> +static inline bool lruvec_holds_page_lru_lock(struct page *page,
> +					      struct lruvec *lruvec)
> +{
> +	return lruvec_pgdat(lruvec) == page_pgdat(page) &&
> +	       lruvec_memcg(lruvec) == page_memcg(page);
> +}
> +
>  /* Don't lock again iff page's lruvec locked */
>  static inline struct lruvec *relock_page_lruvec_irq(struct page *page,
>  		struct lruvec *locked_lruvec)
> -- 
> 2.11.0

-- 
Michal Hocko
SUSE Labs