Re: [PATCH 1/2] Resource usage threshold notification addition to res_counter (v3)

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Mon, 13 Jul 2009 17:16:20 -0700
Vladislav Buzov <vbuzov@embeddedalley.com> wrote:

> This patch updates the Resource Counter to add a configurable resource usage
> threshold notification mechanism.
> 
> Signed-off-by: Vladislav Buzov <vbuzov@embeddedalley.com>
> Signed-off-by: Dan Malek <dan@embeddedalley.com>
> ---
>  Documentation/cgroups/resource_counter.txt |   21 ++++++++-
>  include/linux/res_counter.h                |   69 ++++++++++++++++++++++++++++
>  kernel/res_counter.c                       |    7 +++
>  3 files changed, 95 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/cgroups/resource_counter.txt b/Documentation/cgroups/resource_counter.txt
> index 95b24d7..1369dff 100644
> --- a/Documentation/cgroups/resource_counter.txt
> +++ b/Documentation/cgroups/resource_counter.txt
> @@ -39,7 +39,20 @@ to work with it.
>   	The failcnt stands for "failures counter". This is the number of
>  	resource allocation attempts that failed.
>  
> - c. spinlock_t lock
> + e. unsigned long long threshold
> +
> + 	The resource usage threshold to notify the resouce controller. This is
> +	the minimal difference between the resource limit and current usage
> +	to fire a notification.
> +
> + f. void (*threshold_notifier)(struct res_counter *counter)
> +
> +	The threshold notification callback installed by the resource
> +	controller. Called when the usage reaches or exceeds the threshold.
> +	Should be fast and not sleep because called when interrupts are
> +	disabled.
> +

This interface isn't very useful..hard to use..can't you just return the result as
"exceeds threshold" to the callers ?

If I was you, I'll add following state to res_counter

enum {
	RES_BELOW_THRESH,
	RES_OVER_THRESH,
} res_state;

struct res_counter {
	.....
	enum	res_state	state;
}

Then, caller does
example)
	prev_state = res->state;
	res_counter_charge(res....)
	if (prev_state != res->state)
		do_xxxxx..

notifier under spinlock is not usual interface. And if this is "notifier",
something generic, notifier_call_chain should be used rather than original
one, IIUC.

So, avoiding to use "callback" is a way to go, I think.

Thanks,
-Kame




> + g. spinlock_t lock
>  
>   	Protects changes of the above values.
>  
> @@ -140,6 +153,7 @@ counter fields. They are recommended to adhere to the following rules:
>  	usage		usage_in_<unit_of_measurement>
>  	max_usage	max_usage_in_<unit_of_measurement>
>  	limit		limit_in_<unit_of_measurement>
> +	threshold	notify_threshold_in_<unit_of_measurement>
>  	failcnt		failcnt
>  	lock		no file :)
>  
> @@ -153,9 +167,12 @@ counter fields. They are recommended to adhere to the following rules:
>  	usage		prohibited
>  	max_usage	reset to usage
>  	limit		set the limit
> +	threshold	set the threshold
>  	failcnt		reset to zero
>  
> -
> + d. Notification is enabled by installing the threshold notifier callback. It
> +    is up to the resouce controller to communicate the notification to user
> +    space tasks.
>  
>  5. Usage example
>  
> diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h
> index 511f42f..5ec98d7 100644
> --- a/include/linux/res_counter.h
> +++ b/include/linux/res_counter.h
> @@ -9,6 +9,11 @@
>   *
>   * Author: Pavel Emelianov <xemul@openvz.org>
>   *
> + * Resouce usage threshold notification update
> + * Copyright 2009 CE Linux Forum and Embedded Alley Solutions, Inc.
> + * Author: Dan Malek <dan@embeddedalley.com>
> + * Author: Vladislav Buzov <vbuzov@embeddedalley.com>
> + *
>   * See Documentation/cgroups/resource_counter.txt for more
>   * info about what this counter is.
>   */
> @@ -35,6 +40,19 @@ struct res_counter {
>  	 */
>  	unsigned long long limit;
>  	/*
> +	 * the resource usage threshold to notify the resouce controller. This
> +	 * is the minimal difference between the resource limit and current
> +	 * usage to fire a notification.
> +	 */
> +	unsigned long long threshold;
> +	/*
> +	 * the threshold notification callback installed by the resource
> +	 * controller. Called when the usage reaches or exceeds the threshold.
> +	 * Should be fast and not sleep because called when interrupts are
> +	 * disabled.
> +	 */
> +	void (*threshold_notifier)(struct res_counter *counter);
> +	/*
>  	 * the number of unsuccessful attempts to consume the resource
>  	 */
>  	unsigned long long failcnt;
> @@ -87,6 +105,7 @@ enum {
>  	RES_MAX_USAGE,
>  	RES_LIMIT,
>  	RES_FAILCNT,
> +	RES_THRESHOLD,
>  };
>  
>  /*
> @@ -132,6 +151,21 @@ static inline bool res_counter_limit_check_locked(struct res_counter *cnt)
>  	return false;
>  }
>  
> +static inline bool res_counter_threshold_check_locked(struct res_counter *cnt)
> +{
> +	if (cnt->usage + cnt->threshold < cnt->limit)
> +		return true;
> +
> +	return false;
> +}
> +
> +static inline void res_counter_threshold_notify_locked(struct res_counter *cnt)
> +{
> +	if (!res_counter_threshold_check_locked(cnt) &&
> +	    cnt->threshold_notifier)
> +		cnt->threshold_notifier(cnt);
> +}
> +
>  /*
>   * Helper function to detect if the cgroup is within it's limit or
>   * not. It's currently called from cgroup_rss_prepare()
> @@ -147,6 +181,21 @@ static inline bool res_counter_check_under_limit(struct res_counter *cnt)
>  	return ret;
>  }
>  
> +/*
> + * Helper function to detect if the cgroup usage is under it's threshold or
> + * not.
> + */
> +static inline bool res_counter_check_under_threshold(struct res_counter *cnt)
> +{
> +	bool ret;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&cnt->lock, flags);
> +	ret = res_counter_threshold_check_locked(cnt);
> +	spin_unlock_irqrestore(&cnt->lock, flags);
> +	return ret;
> +}
> +
>  static inline void res_counter_reset_max(struct res_counter *cnt)
>  {
>  	unsigned long flags;
> @@ -174,6 +223,26 @@ static inline int res_counter_set_limit(struct res_counter *cnt,
>  	spin_lock_irqsave(&cnt->lock, flags);
>  	if (cnt->usage <= limit) {
>  		cnt->limit = limit;
> +		if (limit <= cnt->threshold)
> +			cnt->threshold = 0;
> +		else
> +			res_counter_threshold_notify_locked(cnt);
> +		ret = 0;
> +	}
> +	spin_unlock_irqrestore(&cnt->lock, flags);
> +	return ret;
> +}
> +
> +static inline int res_counter_set_threshold(struct res_counter *cnt,
> +		unsigned long long threshold)
> +{
> +	unsigned long flags;
> +	int ret = -EINVAL;
> +
> +	spin_lock_irqsave(&cnt->lock, flags);
> +	if (cnt->limit > threshold) {
> +		cnt->threshold = threshold;
> +		res_counter_threshold_notify_locked(cnt);
>  		ret = 0;
>  	}
>  	spin_unlock_irqrestore(&cnt->lock, flags);
> diff --git a/kernel/res_counter.c b/kernel/res_counter.c
> index e1338f0..9b36748 100644
> --- a/kernel/res_counter.c
> +++ b/kernel/res_counter.c
> @@ -5,6 +5,10 @@
>   *
>   * Author: Pavel Emelianov <xemul@openvz.org>
>   *
> + * Resouce usage threshold notification update
> + * Copyright 2009 CE Linux Forum and Embedded Alley Solutions, Inc.
> + * Author: Dan Malek <dan@embeddedalley.com>
> + * Author: Vladislav Buzov <vbuzov@embeddedalley.com>
>   */
>  
>  #include <linux/types.h>
> @@ -32,6 +36,7 @@ int res_counter_charge_locked(struct res_counter *counter, unsigned long val)
>  	counter->usage += val;
>  	if (counter->usage > counter->max_usage)
>  		counter->max_usage = counter->usage;
> +	res_counter_threshold_notify_locked(counter);
>  	return 0;
>  }
>  
> @@ -101,6 +106,8 @@ res_counter_member(struct res_counter *counter, int member)
>  		return &counter->limit;
>  	case RES_FAILCNT:
>  		return &counter->failcnt;
> +	case RES_THRESHOLD:
> +		return &counter->threshold;
>  	};
>  
>  	BUG();
> -- 
> 1.5.6.3
> 
> 

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