Re: [RFC][PATCH 1/2] add res_counter_usage_safe

[Michal Hocko <mhocko@suse.cz>]

On Thu 28-06-12 19:20:58, KAMEZAWA Hiroyuki wrote:
> This series is a cleaned up patches discussed in a few days ago, the topic
> was how to make compaction works well even if there is a memcg under OOM.
> ==
> memcg: add res_counter_usage_safe()
> 
> I think usage > limit means a sign of BUG. But, sometimes,
> res_counter_charge_nofail() is very convenient. tcp_memcg uses it.
> And I'd like to use it for helping page migration.
> 
> This patch adds res_counter_usage_safe() which returns min(usage,limit).
> By this we can use res_counter_charge_nofail() without breaking
> user experience.
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

Reviewed-by: Michal Hocko <mhocko@suse.cz>

> ---
>  include/linux/res_counter.h |    2 ++
>  kernel/res_counter.c        |   15 +++++++++++++++
>  net/ipv4/tcp_memcontrol.c   |    2 +-
>  3 files changed, 18 insertions(+), 1 deletions(-)
> 
> diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h
> index 7d7fbe2..a6f8cc5 100644
> --- a/include/linux/res_counter.h
> +++ b/include/linux/res_counter.h
> @@ -226,4 +226,6 @@ res_counter_set_soft_limit(struct res_counter *cnt,
>  	return 0;
>  }
>  
> +u64 res_counter_usage_safe(struct res_counter *cnt);
> +
>  #endif
> diff --git a/kernel/res_counter.c b/kernel/res_counter.c
> index ad581aa..e84149b 100644
> --- a/kernel/res_counter.c
> +++ b/kernel/res_counter.c
> @@ -171,6 +171,21 @@ u64 res_counter_read_u64(struct res_counter *counter, int member)
>  }
>  #endif
>  
> +/*
> + * Returns usage. If usage > limit, limit is returned.
> + * This is useful not to break user experiance if the excess
> + * is temporal.
> + */
> +u64 res_counter_usage_safe(struct res_counter *counter)
> +{
> +	u64 usage, limit;
> +
> +	limit = res_counter_read_u64(counter, RES_LIMIT);
> +	usage = res_counter_read_u64(counter, RES_USAGE);
> +
> +	return min(usage, limit);
> +}
> +
>  int res_counter_memparse_write_strategy(const char *buf,
>  					unsigned long long *res)
>  {
> diff --git a/net/ipv4/tcp_memcontrol.c b/net/ipv4/tcp_memcontrol.c
> index b6f3583..a73dce6 100644
> --- a/net/ipv4/tcp_memcontrol.c
> +++ b/net/ipv4/tcp_memcontrol.c
> @@ -180,7 +180,7 @@ static u64 tcp_read_usage(struct mem_cgroup *memcg)
>  		return atomic_long_read(&tcp_memory_allocated) << PAGE_SHIFT;
>  
>  	tcp = tcp_from_cgproto(cg_proto);
> -	return res_counter_read_u64(&tcp->tcp_memory_allocated, RES_USAGE);
> +	return res_counter_usage_safe(&tcp->tcp_memory_allocated);
>  }
>  
>  static u64 tcp_cgroup_read(struct cgroup *cont, struct cftype *cft)
> -- 
> 1.7.4.1
> 
> 

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic

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