linux-kernel - Re: [patch 1/8] mm: memcg: remove unnecessary preemption disabling

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Message-ID: <20140210141713.GG7117@dhcp22.suse.cz>
Date:	Mon, 10 Feb 2014 15:17:13 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 1/8] mm: memcg: remove unnecessary preemption disabling

On Fri 07-02-14 12:04:18, Johannes Weiner wrote:
> lock_page_cgroup() disables preemption, remove explicit preemption
> disabling for code paths holding this lock.
> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

It would be better to document the dependency on lock_page_cgroup. But
the patch looks correct.

Acked-by: Michal Hocko <mhocko@...e.cz>

> ---
>  mm/memcontrol.c | 15 ++++-----------
>  1 file changed, 4 insertions(+), 11 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 53385cd4e6f0..befb3dd9d46c 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -921,8 +921,6 @@ static void mem_cgroup_charge_statistics(struct mem_cgroup *memcg,
>  					 struct page *page,
>  					 bool anon, int nr_pages)
>  {
> -	preempt_disable();
> -
>  	/*
>  	 * Here, RSS means 'mapped anon' and anon's SwapCache. Shmem/tmpfs is
>  	 * counted as CACHE even if it's on ANON LRU.
> @@ -947,8 +945,6 @@ static void mem_cgroup_charge_statistics(struct mem_cgroup *memcg,
>  	}
>  
>  	__this_cpu_add(memcg->stat->nr_page_events, nr_pages);
> -
> -	preempt_enable();
>  }
>  
>  unsigned long
> @@ -3780,17 +3776,14 @@ void mem_cgroup_split_huge_fixup(struct page *head)
>  }
>  #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
>  
> -static inline
> -void mem_cgroup_move_account_page_stat(struct mem_cgroup *from,
> -					struct mem_cgroup *to,
> -					unsigned int nr_pages,
> -					enum mem_cgroup_stat_index idx)
> +static void mem_cgroup_move_account_page_stat(struct mem_cgroup *from,
> +					      struct mem_cgroup *to,
> +					      unsigned int nr_pages,
> +					      enum mem_cgroup_stat_index idx)
>  {
>  	/* Update stat data for mem_cgroup */
> -	preempt_disable();
>  	__this_cpu_sub(from->stat->count[idx], nr_pages);
>  	__this_cpu_add(to->stat->count[idx], nr_pages);
> -	preempt_enable();
>  }
>  
>  /**
> -- 
> 1.8.5.3
> 

-- 
Michal Hocko
SUSE Labs
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