kernel: res_counter: remove the unused API

2.1. Design

The core of the design is a counter called the res_counter. The res_counter

tracks the current memory usage and limit of the group of processes associated

with the controller. Each cgroup has a memory controller specific data

structure (mem_cgroup) associated with it.

The core of the design is a counter called the page_counter. The

page_counter tracks the current memory usage and limit of the group of

processes associated with the controller. Each cgroup has a memory controller

specific data structure (mem_cgroup) associated with it.

2.2. Accounting

		+--------------------+

		|  mem_cgroup        |

		|  (res_counter)     |

		|  (page_counter)    |

		+--------------------+

		 /            ^      \

		/             |       \

0. Configuration

a. Enable CONFIG_CGROUPS

b. Enable CONFIG_RESOURCE_COUNTERS

c. Enable CONFIG_MEMCG

d. Enable CONFIG_MEMCG_SWAP (to use swap extension)

b. Enable CONFIG_MEMCG

c. Enable CONFIG_MEMCG_SWAP (to use swap extension)

d. Enable CONFIG_MEMCG_KMEM (to use kmem extension)

1. Prepare the cgroups (see cgroups.txt, Why are cgroups needed?)

		The Resource Counter

The resource counter, declared at include/linux/res_counter.h,

is supposed to facilitate the resource management by controllers

by providing common stuff for accounting.

This "stuff" includes the res_counter structure and routines

to work with it.

1. Crucial parts of the res_counter structure

 a. unsigned long long usage

 	The usage value shows the amount of a resource that is consumed

	by a group at a given time. The units of measurement should be

	determined by the controller that uses this counter. E.g. it can

	be bytes, items or any other unit the controller operates on.

 b. unsigned long long max_usage

 	The maximal value of the usage over time.

 	This value is useful when gathering statistical information about

	the particular group, as it shows the actual resource requirements

	for a particular group, not just some usage snapshot.

 c. unsigned long long limit

 	The maximal allowed amount of resource to consume by the group. In

	case the group requests for more resources, so that the usage value

	would exceed the limit, the resource allocation is rejected (see

	the next section).

 d. unsigned long long failcnt

 	The failcnt stands for "failures counter". This is the number of

	resource allocation attempts that failed.

 c. spinlock_t lock

 	Protects changes of the above values.

2. Basic accounting routines

 a. void res_counter_init(struct res_counter *rc,

				struct res_counter *rc_parent)

 	Initializes the resource counter. As usual, should be the first

	routine called for a new counter.

	The struct res_counter *parent can be used to define a hierarchical

	child -> parent relationship directly in the res_counter structure,

	NULL can be used to define no relationship.

 c. int res_counter_charge(struct res_counter *rc, unsigned long val,

				struct res_counter **limit_fail_at)

	When a resource is about to be allocated it has to be accounted

	with the appropriate resource counter (controller should determine

	which one to use on its own). This operation is called "charging".

	This is not very important which operation - resource allocation

	or charging - is performed first, but

	  * if the allocation is performed first, this may create a

	    temporary resource over-usage by the time resource counter is

	    charged;

	  * if the charging is performed first, then it should be uncharged

	    on error path (if the one is called).

	If the charging fails and a hierarchical dependency exists, the

	limit_fail_at parameter is set to the particular res_counter element

	where the charging failed.

 d. u64 res_counter_uncharge(struct res_counter *rc, unsigned long val)

	When a resource is released (freed) it should be de-accounted

	from the resource counter it was accounted to.  This is called

	"uncharging". The return value of this function indicate the amount

	of charges still present in the counter.

	The _locked routines imply that the res_counter->lock is taken.

 e. u64 res_counter_uncharge_until

		(struct res_counter *rc, struct res_counter *top,

		 unsigned long val)

	Almost same as res_counter_uncharge() but propagation of uncharge

	stops when rc == top. This is useful when kill a res_counter in

	child cgroup.

 2.1 Other accounting routines

    There are more routines that may help you with common needs, like

    checking whether the limit is reached or resetting the max_usage

    value. They are all declared in include/linux/res_counter.h.

3. Analyzing the resource counter registrations

 a. If the failcnt value constantly grows, this means that the counter's

    limit is too tight. Either the group is misbehaving and consumes too

    many resources, or the configuration is not suitable for the group

    and the limit should be increased.

 b. The max_usage value can be used to quickly tune the group. One may

    set the limits to maximal values and either load the container with

    a common pattern or leave one for a while. After this the max_usage

    value shows the amount of memory the container would require during

    its common activity.

    Setting the limit a bit above this value gives a pretty good

    configuration that works in most of the cases.

 c. If the max_usage is much less than the limit, but the failcnt value

    is growing, then the group tries to allocate a big chunk of resource

    at once.

 d. If the max_usage is much less than the limit, but the failcnt value

    is 0, then this group is given too high limit, that it does not

    require. It is better to lower the limit a bit leaving more resource

    for other groups.

4. Communication with the control groups subsystem (cgroups)

All the resource controllers that are using cgroups and resource counters

should provide files (in the cgroup filesystem) to work with the resource

counter fields. They are recommended to adhere to the following rules:

 a. File names

 	Field name	File name

	---------------------------------------------------

	usage		usage_in_<unit_of_measurement>

	max_usage	max_usage_in_<unit_of_measurement>

	limit		limit_in_<unit_of_measurement>

	failcnt		failcnt

	lock		no file :)

 b. Reading from file should show the corresponding field value in the

    appropriate format.

 c. Writing to file

 	Field		Expected behavior

	----------------------------------

	usage		prohibited

	max_usage	reset to usage

	limit		set the limit

	failcnt		reset to zero

5. Usage example

 a. Declare a task group (take a look at cgroups subsystem for this) and

    fold a res_counter into it

	struct my_group {

		struct res_counter res;

		<other fields>

	}

 b. Put hooks in resource allocation/release paths

 	int alloc_something(...)

	{

		if (res_counter_charge(res_counter_ptr, amount) < 0)

			return -ENOMEM;

		<allocate the resource and return to the caller>

	}

	void release_something(...)

	{

		res_counter_uncharge(res_counter_ptr, amount);

		<release the resource>

	}

    In order to keep the usage value self-consistent, both the

    "res_counter_ptr" and the "amount" in release_something() should be

    the same as they were in the alloc_something() when the releasing

    resource was allocated.

 c. Provide the way to read res_counter values and set them (the cgroups

    still can help with it).

 c. Compile and run :)

#ifndef __RES_COUNTER_H__

#define __RES_COUNTER_H__

/*

 * Resource Counters

 * Contain common data types and routines for resource accounting

 *

 * Copyright 2007 OpenVZ SWsoft Inc

 *

 * Author: Pavel Emelianov <xemul@openvz.org>

 *

 * See Documentation/cgroups/resource_counter.txt for more

 * info about what this counter is.

 */

#include <linux/spinlock.h>

#include <linux/errno.h>

/*

 * The core object. the cgroup that wishes to account for some

 * resource may include this counter into its structures and use

 * the helpers described beyond

 */

struct res_counter {

	/*

	 * the current resource consumption level

	 */

	unsigned long long usage;

	/*

	 * the maximal value of the usage from the counter creation

	 */

	unsigned long long max_usage;

	/*

	 * the limit that usage cannot exceed

	 */

	unsigned long long limit;

	/*

	 * the limit that usage can be exceed

	 */

	unsigned long long soft_limit;

	/*

	 * the number of unsuccessful attempts to consume the resource

	 */

	unsigned long long failcnt;

	/*

	 * the lock to protect all of the above.

	 * the routines below consider this to be IRQ-safe

	 */

	spinlock_t lock;

	/*

	 * Parent counter, used for hierarchial resource accounting

	 */

	struct res_counter *parent;

};

#define RES_COUNTER_MAX ULLONG_MAX

/**

 * Helpers to interact with userspace

 * res_counter_read_u64() - returns the value of the specified member.

 * res_counter_read/_write - put/get the specified fields from the

 * res_counter struct to/from the user

 *

 * @counter:     the counter in question

 * @member:  the field to work with (see RES_xxx below)

 * @buf:     the buffer to opeate on,...

 * @nbytes:  its size...

 * @pos:     and the offset.

 */

u64 res_counter_read_u64(struct res_counter *counter, int member);

ssize_t res_counter_read(struct res_counter *counter, int member,

		const char __user *buf, size_t nbytes, loff_t *pos,

		int (*read_strategy)(unsigned long long val, char *s));

int res_counter_memparse_write_strategy(const char *buf,

					unsigned long long *res);

/*

 * the field descriptors. one for each member of res_counter

 */

enum {

	RES_USAGE,

	RES_MAX_USAGE,

	RES_LIMIT,

	RES_FAILCNT,

	RES_SOFT_LIMIT,

};

/*

 * helpers for accounting

 */

void res_counter_init(struct res_counter *counter, struct res_counter *parent);

/*

 * charge - try to consume more resource.

 *

 * @counter: the counter

 * @val: the amount of the resource. each controller defines its own

 *       units, e.g. numbers, bytes, Kbytes, etc

 *

 * returns 0 on success and <0 if the counter->usage will exceed the

 * counter->limit

 *

 * charge_nofail works the same, except that it charges the resource

 * counter unconditionally, and returns < 0 if the after the current

 * charge we are over limit.

 */

int __must_check res_counter_charge(struct res_counter *counter,

		unsigned long val, struct res_counter **limit_fail_at);

int res_counter_charge_nofail(struct res_counter *counter,

		unsigned long val, struct res_counter **limit_fail_at);

/*

 * uncharge - tell that some portion of the resource is released

 *

 * @counter: the counter

 * @val: the amount of the resource

 *

 * these calls check for usage underflow and show a warning on the console

 *

 * returns the total charges still present in @counter.

 */

u64 res_counter_uncharge(struct res_counter *counter, unsigned long val);

u64 res_counter_uncharge_until(struct res_counter *counter,

			       struct res_counter *top,

			       unsigned long val);

/**

 * res_counter_margin - calculate chargeable space of a counter

 * @cnt: the counter

 *

 * Returns the difference between the hard limit and the current usage

 * of resource counter @cnt.

 */

static inline unsigned long long res_counter_margin(struct res_counter *cnt)

{

	unsigned long long margin;

	unsigned long flags;

	spin_lock_irqsave(&cnt->lock, flags);

	if (cnt->limit > cnt->usage)

		margin = cnt->limit - cnt->usage;

	else

		margin = 0;

	spin_unlock_irqrestore(&cnt->lock, flags);

	return margin;

}

/**

 * Get the difference between the usage and the soft limit

 * @cnt: The counter

 *

 * Returns 0 if usage is less than or equal to soft limit

 * The difference between usage and soft limit, otherwise.

 */

static inline unsigned long long

res_counter_soft_limit_excess(struct res_counter *cnt)

{

	unsigned long long excess;

	unsigned long flags;

	spin_lock_irqsave(&cnt->lock, flags);

	if (cnt->usage <= cnt->soft_limit)

		excess = 0;

	else

		excess = cnt->usage - cnt->soft_limit;

	spin_unlock_irqrestore(&cnt->lock, flags);

	return excess;

}

static inline void res_counter_reset_max(struct res_counter *cnt)

{

	unsigned long flags;

	spin_lock_irqsave(&cnt->lock, flags);

	cnt->max_usage = cnt->usage;

	spin_unlock_irqrestore(&cnt->lock, flags);

}

static inline void res_counter_reset_failcnt(struct res_counter *cnt)

{

	unsigned long flags;

	spin_lock_irqsave(&cnt->lock, flags);

	cnt->failcnt = 0;

	spin_unlock_irqrestore(&cnt->lock, flags);

}

static inline int res_counter_set_limit(struct res_counter *cnt,

		unsigned long long limit)

{

	unsigned long flags;

	int ret = -EBUSY;

	spin_lock_irqsave(&cnt->lock, flags);

	if (cnt->usage <= limit) {

		cnt->limit = limit;

		ret = 0;

	}

	spin_unlock_irqrestore(&cnt->lock, flags);

	return ret;

}

static inline int

res_counter_set_soft_limit(struct res_counter *cnt,

				unsigned long long soft_limit)

{

	unsigned long flags;

	spin_lock_irqsave(&cnt->lock, flags);

	cnt->soft_limit = soft_limit;

	spin_unlock_irqrestore(&cnt->lock, flags);

	return 0;

}

#endif

	  Provides a simple Resource Controller for monitoring the

	  total CPU consumed by the tasks in a cgroup.

config RESOURCE_COUNTERS

	bool "Resource counters"

	help

	  This option enables controller independent resource accounting

	  infrastructure that works with cgroups.

config PAGE_COUNTER

       bool

obj-$(CONFIG_USER_NS) += user_namespace.o

obj-$(CONFIG_PID_NS) += pid_namespace.o

obj-$(CONFIG_IKCONFIG) += configs.o

obj-$(CONFIG_RESOURCE_COUNTERS) += res_counter.o

obj-$(CONFIG_SMP) += stop_machine.o

obj-$(CONFIG_KPROBES_SANITY_TEST) += test_kprobes.o

obj-$(CONFIG_AUDIT) += audit.o auditfilter.o