Re: [patch 04/11] mm, memcg: add tunable for oom reserves

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 4 Mar 2014 19:59:19 -0800 (PST) David Rientjes <rientjes@google.com> wrote:

> Userspace needs a way to define the amount of memory reserves that
> processes handling oom conditions may utilize.  This patch adds a per-
> memcg oom reserve field and file, memory.oom_reserve_in_bytes, to
> manipulate its value.
> 
> If currently utilized memory reserves are attempted to be reduced by
> writing a smaller value to memory.oom_reserve_in_bytes, it will fail with
> -EBUSY until some memory is uncharged.
> 
> ...
>
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -315,6 +315,9 @@ struct mem_cgroup {
>  	/* OOM-Killer disable */
>  	int		oom_kill_disable;
>  
> +	/* reserves for handling oom conditions, protected by res.lock */
> +	unsigned long long	oom_reserve;

Units?  bytes, I assume.

>  	/* set when res.limit == memsw.limit */
>  	bool		memsw_is_minimum;
>  
> @@ -5936,6 +5939,51 @@ static int mem_cgroup_oom_control_write(struct cgroup_subsys_state *css,
>  	return 0;
>  }
>  
> +static int mem_cgroup_resize_oom_reserve(struct mem_cgroup *memcg,
> +					 unsigned long long new_limit)
> +{
> +	struct res_counter *res = &memcg->res;
> +	u64 limit, usage;
> +	int ret = 0;

The code mixes u64's and unsigned long longs in inexplicable ways. 
Suggest using u64 throughout.

> +	spin_lock(&res->lock);
> +	limit = res->limit;
> +	usage = res->usage;
> +
> +	if (usage > limit && usage - limit > new_limit) {
> +		ret = -EBUSY;
> +		goto out;
> +	}
> +
> +	memcg->oom_reserve = new_limit;
> +out:
> +	spin_unlock(&res->lock);
> +	return ret;
> +}
>
> ...
>

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