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From: Michal Hocko <mhocko@suse.com>
To: Shakeel Butt <shakeelb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>,
	Roman Gushchin <guro@fb.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	cgroups@vger.kernel.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] memcg: cleanup racy sum avoidance code
Date: Mon, 2 Aug 2021 08:57:56 +0200	[thread overview]
Message-ID: <YQeXdPV8cUNIOUB5@dhcp22.suse.cz> (raw)
In-Reply-To: <20210728012243.3369123-1-shakeelb@google.com>

On Tue 27-07-21 18:22:43, Shakeel Butt wrote:
> We used to have per-cpu memcg and lruvec stats and the readers have to
> traverse and sum the stats from each cpu. This summing was racy and may
> expose transient negative values. So, an explicit check was added to
> avoid such scenarios. Now these stats are moved to rstat infrastructure
> and are no more per-cpu, so we can remove the fixup for transient
> negative values.
> 
> Signed-off-by: Shakeel Butt <shakeelb@google.com>

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

> ---
>  include/linux/memcontrol.h | 15 ++-------------
>  1 file changed, 2 insertions(+), 13 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 7028d8e4a3d7..5f2a39a43d47 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -991,30 +991,19 @@ static inline void mod_memcg_state(struct mem_cgroup *memcg,
>  
>  static inline unsigned long memcg_page_state(struct mem_cgroup *memcg, int idx)
>  {
> -	long x = READ_ONCE(memcg->vmstats.state[idx]);
> -#ifdef CONFIG_SMP
> -	if (x < 0)
> -		x = 0;
> -#endif
> -	return x;
> +	return READ_ONCE(memcg->vmstats.state[idx]);
>  }
>  
>  static inline unsigned long lruvec_page_state(struct lruvec *lruvec,
>  					      enum node_stat_item idx)
>  {
>  	struct mem_cgroup_per_node *pn;
> -	long x;
>  
>  	if (mem_cgroup_disabled())
>  		return node_page_state(lruvec_pgdat(lruvec), idx);
>  
>  	pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
> -	x = READ_ONCE(pn->lruvec_stats.state[idx]);
> -#ifdef CONFIG_SMP
> -	if (x < 0)
> -		x = 0;
> -#endif
> -	return x;
> +	return READ_ONCE(pn->lruvec_stats.state[idx]);
>  }
>  
>  static inline unsigned long lruvec_page_state_local(struct lruvec *lruvec,
> -- 
> 2.32.0.432.gabb21c7263-goog

-- 
Michal Hocko
SUSE Labs

      parent reply	other threads:[~2021-08-02  6:58 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-28  1:22 Shakeel Butt
2021-07-28  2:36 ` Roman Gushchin
2021-07-28  8:21 ` David Hildenbrand
2021-07-28 19:43 ` Andrew Morton
2021-07-28 20:37   ` Shakeel Butt
2021-08-02  6:57 ` Michal Hocko [this message]

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