[linux.git] / lib / percpu_ida.c

/*
 * Percpu IDA library
 *
 * Copyright (C) 2013 Datera, Inc. Kent Overstreet
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2, or (at
 * your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 */

#include <linux/bitmap.h>
#include <linux/bitops.h>
#include <linux/bug.h>
#include <linux/err.h>
#include <linux/export.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/percpu.h>
#include <linux/sched.h>
#include <linux/string.h>
#include <linux/spinlock.h>
#include <linux/percpu_ida.h>

struct percpu_ida_cpu {
	/*
	 * Even though this is percpu, we need a lock for tag stealing by remote
	 * CPUs:
	 */
	spinlock_t			lock;

	/* nr_free/freelist form a stack of free IDs */
	unsigned			nr_free;
	unsigned			freelist[];
};

static inline void move_tags(unsigned *dst, unsigned *dst_nr,
			     unsigned *src, unsigned *src_nr,
			     unsigned nr)
{
	*src_nr -= nr;
	memcpy(dst + *dst_nr, src + *src_nr, sizeof(unsigned) * nr);
	*dst_nr += nr;
}

/*
 * Try to steal tags from a remote cpu's percpu freelist.
 *
 * We first check how many percpu freelists have tags
 *
 * Then we iterate through the cpus until we find some tags - we don't attempt
 * to find the "best" cpu to steal from, to keep cacheline bouncing to a
 * minimum.
 */
static inline void steal_tags(struct percpu_ida *pool,
			      struct percpu_ida_cpu *tags)
{
	unsigned cpus_have_tags, cpu = pool->cpu_last_stolen;
	struct percpu_ida_cpu *remote;

	for (cpus_have_tags = cpumask_weight(&pool->cpus_have_tags);
	     cpus_have_tags; cpus_have_tags--) {
		cpu = cpumask_next(cpu, &pool->cpus_have_tags);

		if (cpu >= nr_cpu_ids) {
			cpu = cpumask_first(&pool->cpus_have_tags);
			if (cpu >= nr_cpu_ids)
				BUG();
		}

		pool->cpu_last_stolen = cpu;
		remote = per_cpu_ptr(pool->tag_cpu, cpu);

		cpumask_clear_cpu(cpu, &pool->cpus_have_tags);

		if (remote == tags)
			continue;

		spin_lock(&remote->lock);

		if (remote->nr_free) {
			memcpy(tags->freelist,
			       remote->freelist,
			       sizeof(unsigned) * remote->nr_free);

			tags->nr_free = remote->nr_free;
			remote->nr_free = 0;
		}

		spin_unlock(&remote->lock);

		if (tags->nr_free)
			break;
	}
}

/*
 * Pop up to IDA_PCPU_BATCH_MOVE IDs off the global freelist, and push them onto
 * our percpu freelist:
 */
static inline void alloc_global_tags(struct percpu_ida *pool,
				     struct percpu_ida_cpu *tags)
{
	move_tags(tags->freelist, &tags->nr_free,
		  pool->freelist, &pool->nr_free,
		  min(pool->nr_free, pool->percpu_batch_size));
}

static inline unsigned alloc_local_tag(struct percpu_ida_cpu *tags)
{
	int tag = -ENOSPC;

	spin_lock(&tags->lock);
	if (tags->nr_free)
		tag = tags->freelist[--tags->nr_free];
	spin_unlock(&tags->lock);

	return tag;
}

/**
 * percpu_ida_alloc - allocate a tag
 * @pool: pool to allocate from
 * @state: task state for prepare_to_wait
 *
 * Returns a tag - an integer in the range [0..nr_tags) (passed to
 * tag_pool_init()), or otherwise -ENOSPC on allocation failure.
 *
 * Safe to be called from interrupt context (assuming it isn't passed
 * TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE, of course).
 *
 * @gfp indicates whether or not to wait until a free id is available (it's not
 * used for internal memory allocations); thus if passed __GFP_RECLAIM we may sleep
 * however long it takes until another thread frees an id (same semantics as a
 * mempool).
 *
 * Will not fail if passed TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE.
 */
int percpu_ida_alloc(struct percpu_ida *pool, int state)
{
	DEFINE_WAIT(wait);
	struct percpu_ida_cpu *tags;
	unsigned long flags;
	int tag;

	local_irq_save(flags);
	tags = this_cpu_ptr(pool->tag_cpu);

	/* Fastpath */
	tag = alloc_local_tag(tags);
	if (likely(tag >= 0)) {
		local_irq_restore(flags);
		return tag;
	}

	while (1) {
		spin_lock(&pool->lock);

		/*
		 * prepare_to_wait() must come before steal_tags(), in case
		 * percpu_ida_free() on another cpu flips a bit in
		 * cpus_have_tags
		 *
		 * global lock held and irqs disabled, don't need percpu lock
		 */
		if (state != TASK_RUNNING)
			prepare_to_wait(&pool->wait, &wait, state);

		if (!tags->nr_free)
			alloc_global_tags(pool, tags);
		if (!tags->nr_free)
			steal_tags(pool, tags);

		if (tags->nr_free) {
			tag = tags->freelist[--tags->nr_free];
			if (tags->nr_free)
				cpumask_set_cpu(smp_processor_id(),
						&pool->cpus_have_tags);
		}

		spin_unlock(&pool->lock);
		local_irq_restore(flags);

		if (tag >= 0 || state == TASK_RUNNING)
			break;

		if (signal_pending_state(state, current)) {
			tag = -ERESTARTSYS;
			break;
		}

		schedule();

		local_irq_save(flags);
		tags = this_cpu_ptr(pool->tag_cpu);
	}
	if (state != TASK_RUNNING)
		finish_wait(&pool->wait, &wait);

	return tag;
}
EXPORT_SYMBOL_GPL(percpu_ida_alloc);

/**
 * percpu_ida_free - free a tag
 * @pool: pool @tag was allocated from
 * @tag: a tag previously allocated with percpu_ida_alloc()
 *
 * Safe to be called from interrupt context.
 */
void percpu_ida_free(struct percpu_ida *pool, unsigned tag)
{
	struct percpu_ida_cpu *tags;
	unsigned long flags;
	unsigned nr_free;

	BUG_ON(tag >= pool->nr_tags);

	local_irq_save(flags);
	tags = this_cpu_ptr(pool->tag_cpu);

	spin_lock(&tags->lock);
	tags->freelist[tags->nr_free++] = tag;

	nr_free = tags->nr_free;
	spin_unlock(&tags->lock);

	if (nr_free == 1) {
		cpumask_set_cpu(smp_processor_id(),
				&pool->cpus_have_tags);
		wake_up(&pool->wait);
	}

	if (nr_free == pool->percpu_max_size) {
		spin_lock(&pool->lock);

		/*
		 * Global lock held and irqs disabled, don't need percpu
		 * lock
		 */
		if (tags->nr_free == pool->percpu_max_size) {
			move_tags(pool->freelist, &pool->nr_free,
				  tags->freelist, &tags->nr_free,
				  pool->percpu_batch_size);

			wake_up(&pool->wait);
		}
		spin_unlock(&pool->lock);
	}

	local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(percpu_ida_free);

/**
 * percpu_ida_destroy - release a tag pool's resources
 * @pool: pool to free
 *
 * Frees the resources allocated by percpu_ida_init().
 */
void percpu_ida_destroy(struct percpu_ida *pool)
{
	free_percpu(pool->tag_cpu);
	free_pages((unsigned long) pool->freelist,
		   get_order(pool->nr_tags * sizeof(unsigned)));
}
EXPORT_SYMBOL_GPL(percpu_ida_destroy);

/**
 * percpu_ida_init - initialize a percpu tag pool
 * @pool: pool to initialize
 * @nr_tags: number of tags that will be available for allocation
 *
 * Initializes @pool so that it can be used to allocate tags - integers in the
 * range [0, nr_tags). Typically, they'll be used by driver code to refer to a
 * preallocated array of tag structures.
 *
 * Allocation is percpu, but sharding is limited by nr_tags - for best
 * performance, the workload should not span more cpus than nr_tags / 128.
 */
int __percpu_ida_init(struct percpu_ida *pool, unsigned long nr_tags,
	unsigned long max_size, unsigned long batch_size)
{
	unsigned i, cpu, order;

	memset(pool, 0, sizeof(*pool));

	init_waitqueue_head(&pool->wait);
	spin_lock_init(&pool->lock);
	pool->nr_tags = nr_tags;
	pool->percpu_max_size = max_size;
	pool->percpu_batch_size = batch_size;

	/* Guard against overflow */
	if (nr_tags > (unsigned) INT_MAX + 1) {
		pr_err("percpu_ida_init(): nr_tags too large\n");
		return -EINVAL;
	}

	order = get_order(nr_tags * sizeof(unsigned));
	pool->freelist = (void *) __get_free_pages(GFP_KERNEL, order);
	if (!pool->freelist)
		return -ENOMEM;

	for (i = 0; i < nr_tags; i++)
		pool->freelist[i] = i;

	pool->nr_free = nr_tags;

	pool->tag_cpu = __alloc_percpu(sizeof(struct percpu_ida_cpu) +
				       pool->percpu_max_size * sizeof(unsigned),
				       sizeof(unsigned));
	if (!pool->tag_cpu)
		goto err;

	for_each_possible_cpu(cpu)
		spin_lock_init(&per_cpu_ptr(pool->tag_cpu, cpu)->lock);

	return 0;
err:
	percpu_ida_destroy(pool);
	return -ENOMEM;
}
EXPORT_SYMBOL_GPL(__percpu_ida_init);

/**
 * percpu_ida_for_each_free - iterate free ids of a pool
 * @pool: pool to iterate
 * @fn: interate callback function
 * @data: parameter for @fn
 *
 * Note, this doesn't guarantee to iterate all free ids restrictly. Some free
 * ids might be missed, some might be iterated duplicated, and some might
 * be iterated and not free soon.
 */
int percpu_ida_for_each_free(struct percpu_ida *pool, percpu_ida_cb fn,
	void *data)
{
	unsigned long flags;
	struct percpu_ida_cpu *remote;
	unsigned cpu, i, err = 0;

	local_irq_save(flags);
	for_each_possible_cpu(cpu) {
		remote = per_cpu_ptr(pool->tag_cpu, cpu);
		spin_lock(&remote->lock);
		for (i = 0; i < remote->nr_free; i++) {
			err = fn(remote->freelist[i], data);
			if (err)
				break;
		}
		spin_unlock(&remote->lock);
		if (err)
			goto out;
	}

	spin_lock(&pool->lock);
	for (i = 0; i < pool->nr_free; i++) {
		err = fn(pool->freelist[i], data);
		if (err)
			break;
	}
	spin_unlock(&pool->lock);
out:
	local_irq_restore(flags);
	return err;
}
EXPORT_SYMBOL_GPL(percpu_ida_for_each_free);

/**
 * percpu_ida_free_tags - return free tags number of a specific cpu or global pool
 * @pool: pool related
 * @cpu: specific cpu or global pool if @cpu == nr_cpu_ids
 *
 * Note: this just returns a snapshot of free tags number.
 */
unsigned percpu_ida_free_tags(struct percpu_ida *pool, int cpu)
{
	struct percpu_ida_cpu *remote;
	if (cpu == nr_cpu_ids)
		return pool->nr_free;
	remote = per_cpu_ptr(pool->tag_cpu, cpu);
	return remote->nr_free;
}
EXPORT_SYMBOL_GPL(percpu_ida_free_tags);
Commit	Line	Data
798ab48e KO	1	/*
	2	* Percpu IDA library
	3	*
	4	* Copyright (C) 2013 Datera, Inc. Kent Overstreet
	5	*
	6	* This program is free software; you can redistribute it and/or
	7	* modify it under the terms of the GNU General Public License as
	8	* published by the Free Software Foundation; either version 2, or (at
	9	* your option) any later version.
	10	*
	11	* This program is distributed in the hope that it will be useful, but
	12	* WITHOUT ANY WARRANTY; without even the implied warranty of
	13	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	14	* General Public License for more details.
	15	*/
	16
	17	#include <linux/bitmap.h>
	18	#include <linux/bitops.h>
	19	#include <linux/bug.h>
	20	#include <linux/err.h>
	21	#include <linux/export.h>
798ab48e KO	22	#include <linux/init.h>
	23	#include <linux/kernel.h>
	24	#include <linux/percpu.h>
	25	#include <linux/sched.h>
798ab48e KO	26	#include <linux/string.h>
	27	#include <linux/spinlock.h>
	28	#include <linux/percpu_ida.h>
	29
798ab48e KO	30	struct percpu_ida_cpu {
	31	/*
	32	* Even though this is percpu, we need a lock for tag stealing by remote
	33	* CPUs:
	34	*/
	35	spinlock_t lock;
	36
	37	/* nr_free/freelist form a stack of free IDs */
	38	unsigned nr_free;
	39	unsigned freelist[];
	40	};
	41
	42	static inline void move_tags(unsigned dst, unsigned dst_nr,
	43	unsigned src, unsigned src_nr,
	44	unsigned nr)
	45	{
	46	*src_nr -= nr;
	47	memcpy(dst + dst_nr, src + src_nr, sizeof(unsigned) * nr);
	48	*dst_nr += nr;
	49	}
	50
	51	/*
	52	* Try to steal tags from a remote cpu's percpu freelist.
	53	*
d835502f	54	* We first check how many percpu freelists have tags
798ab48e KO	55	*
	56	* Then we iterate through the cpus until we find some tags - we don't attempt
	57	* to find the "best" cpu to steal from, to keep cacheline bouncing to a
	58	* minimum.
	59	*/
	60	static inline void steal_tags(struct percpu_ida *pool,
	61	struct percpu_ida_cpu *tags)
	62	{
	63	unsigned cpus_have_tags, cpu = pool->cpu_last_stolen;
	64	struct percpu_ida_cpu *remote;
	65
	66	for (cpus_have_tags = cpumask_weight(&pool->cpus_have_tags);
d835502f	67	cpus_have_tags; cpus_have_tags--) {
798ab48e KO	68	cpu = cpumask_next(cpu, &pool->cpus_have_tags);
	69
	70	if (cpu >= nr_cpu_ids) {
	71	cpu = cpumask_first(&pool->cpus_have_tags);
	72	if (cpu >= nr_cpu_ids)
	73	BUG();
	74	}
	75
	76	pool->cpu_last_stolen = cpu;
	77	remote = per_cpu_ptr(pool->tag_cpu, cpu);
	78
	79	cpumask_clear_cpu(cpu, &pool->cpus_have_tags);
	80
	81	if (remote == tags)
	82	continue;
	83
	84	spin_lock(&remote->lock);
	85
	86	if (remote->nr_free) {
	87	memcpy(tags->freelist,
	88	remote->freelist,
	89	sizeof(unsigned) * remote->nr_free);
	90
	91	tags->nr_free = remote->nr_free;
	92	remote->nr_free = 0;
	93	}
	94
	95	spin_unlock(&remote->lock);
	96
	97	if (tags->nr_free)
	98	break;
	99	}
	100	}
	101
	102	/*
	103	* Pop up to IDA_PCPU_BATCH_MOVE IDs off the global freelist, and push them onto
	104	* our percpu freelist:
	105	*/
	106	static inline void alloc_global_tags(struct percpu_ida *pool,
	107	struct percpu_ida_cpu *tags)
	108	{
	109	move_tags(tags->freelist, &tags->nr_free,
	110	pool->freelist, &pool->nr_free,
e26b53d0	111	min(pool->nr_free, pool->percpu_batch_size));
798ab48e KO	112	}
798ab48e KO	113
6b378382	114	static inline unsigned alloc_local_tag(struct percpu_ida_cpu *tags)
798ab48e KO	115	{
	116	int tag = -ENOSPC;
	117
	118	spin_lock(&tags->lock);
	119	if (tags->nr_free)
	120	tag = tags->freelist[--tags->nr_free];
	121	spin_unlock(&tags->lock);
	122
	123	return tag;
	124	}
	125
	126	/**
	127	* percpu_ida_alloc - allocate a tag
	128	* @pool: pool to allocate from
6f6b5d1e	129	* @state: task state for prepare_to_wait
798ab48e KO	130	*
	131	* Returns a tag - an integer in the range [0..nr_tags) (passed to
	132	* tag_pool_init()), or otherwise -ENOSPC on allocation failure.
	133	*
	134	* Safe to be called from interrupt context (assuming it isn't passed
555b270e	135	* TASK_UNINTERRUPTIBLE \| TASK_INTERRUPTIBLE, of course).
798ab48e KO	136	*
798ab48e KO	137	* @gfp indicates whether or not to wait until a free id is available (it's not
71baba4b	138	* used for internal memory allocations); thus if passed __GFP_RECLAIM we may sleep
798ab48e KO	139	* however long it takes until another thread frees an id (same semantics as a
	140	* mempool).
	141	*
555b270e	142	* Will not fail if passed TASK_UNINTERRUPTIBLE \| TASK_INTERRUPTIBLE.
798ab48e	143	*/
6f6b5d1e	144	int percpu_ida_alloc(struct percpu_ida *pool, int state)
798ab48e KO	145	{
	146	DEFINE_WAIT(wait);
	147	struct percpu_ida_cpu *tags;
	148	unsigned long flags;
	149	int tag;
	150
	151	local_irq_save(flags);
	152	tags = this_cpu_ptr(pool->tag_cpu);
	153
	154	/* Fastpath */
6b378382	155	tag = alloc_local_tag(tags);
798ab48e KO	156	if (likely(tag >= 0)) {
	157	local_irq_restore(flags);
	158	return tag;
	159	}
	160
	161	while (1) {
	162	spin_lock(&pool->lock);
	163
	164	/*
	165	* prepare_to_wait() must come before steal_tags(), in case
	166	* percpu_ida_free() on another cpu flips a bit in
	167	* cpus_have_tags
	168	*
	169	* global lock held and irqs disabled, don't need percpu lock
	170	*/
6f6b5d1e KO	171	if (state != TASK_RUNNING)
6f6b5d1e KO	172	prepare_to_wait(&pool->wait, &wait, state);
798ab48e KO	173
	174	if (!tags->nr_free)
	175	alloc_global_tags(pool, tags);
	176	if (!tags->nr_free)
	177	steal_tags(pool, tags);
	178
	179	if (tags->nr_free) {
	180	tag = tags->freelist[--tags->nr_free];
	181	if (tags->nr_free)
	182	cpumask_set_cpu(smp_processor_id(),
	183	&pool->cpus_have_tags);
	184	}
	185
	186	spin_unlock(&pool->lock);
	187	local_irq_restore(flags);
	188
6f6b5d1e	189	if (tag >= 0 \|\| state == TASK_RUNNING)
798ab48e KO	190	break;
798ab48e KO	191
555b270e NB	192	if (signal_pending_state(state, current)) {
	193	tag = -ERESTARTSYS;
	194	break;
	195	}
	196
798ab48e KO	197	schedule();
	198
	199	local_irq_save(flags);
	200	tags = this_cpu_ptr(pool->tag_cpu);
	201	}
6f6b5d1e KO	202	if (state != TASK_RUNNING)
6f6b5d1e KO	203	finish_wait(&pool->wait, &wait);
798ab48e	204
798ab48e KO	205	return tag;
	206	}
	207	EXPORT_SYMBOL_GPL(percpu_ida_alloc);
	208
	209	/**
	210	* percpu_ida_free - free a tag
	211	* @pool: pool @tag was allocated from
	212	* @tag: a tag previously allocated with percpu_ida_alloc()
	213	*
	214	* Safe to be called from interrupt context.
	215	*/
	216	void percpu_ida_free(struct percpu_ida *pool, unsigned tag)
	217	{
	218	struct percpu_ida_cpu *tags;
	219	unsigned long flags;
	220	unsigned nr_free;
	221
	222	BUG_ON(tag >= pool->nr_tags);
	223
	224	local_irq_save(flags);
	225	tags = this_cpu_ptr(pool->tag_cpu);
	226
	227	spin_lock(&tags->lock);
	228	tags->freelist[tags->nr_free++] = tag;
	229
	230	nr_free = tags->nr_free;
	231	spin_unlock(&tags->lock);
	232
	233	if (nr_free == 1) {
	234	cpumask_set_cpu(smp_processor_id(),
	235	&pool->cpus_have_tags);
	236	wake_up(&pool->wait);
	237	}
	238
e26b53d0	239	if (nr_free == pool->percpu_max_size) {
798ab48e KO	240	spin_lock(&pool->lock);
	241
	242	/*
	243	* Global lock held and irqs disabled, don't need percpu
	244	* lock
	245	*/
e26b53d0	246	if (tags->nr_free == pool->percpu_max_size) {
798ab48e KO	247	move_tags(pool->freelist, &pool->nr_free,
798ab48e KO	248	tags->freelist, &tags->nr_free,
e26b53d0	249	pool->percpu_batch_size);
798ab48e KO	250
	251	wake_up(&pool->wait);
	252	}
	253	spin_unlock(&pool->lock);
	254	}
	255
	256	local_irq_restore(flags);
	257	}
	258	EXPORT_SYMBOL_GPL(percpu_ida_free);
	259
	260	/**
	261	* percpu_ida_destroy - release a tag pool's resources
	262	* @pool: pool to free
	263	*
	264	* Frees the resources allocated by percpu_ida_init().
	265	*/
	266	void percpu_ida_destroy(struct percpu_ida *pool)
	267	{
	268	free_percpu(pool->tag_cpu);
	269	free_pages((unsigned long) pool->freelist,
	270	get_order(pool->nr_tags * sizeof(unsigned)));
	271	}
	272	EXPORT_SYMBOL_GPL(percpu_ida_destroy);
	273
	274	/**
	275	* percpu_ida_init - initialize a percpu tag pool
	276	* @pool: pool to initialize
	277	* @nr_tags: number of tags that will be available for allocation
	278	*
	279	* Initializes @pool so that it can be used to allocate tags - integers in the
	280	* range [0, nr_tags). Typically, they'll be used by driver code to refer to a
	281	* preallocated array of tag structures.
	282	*
	283	* Allocation is percpu, but sharding is limited by nr_tags - for best
	284	* performance, the workload should not span more cpus than nr_tags / 128.
	285	*/
e26b53d0 SL	286	int __percpu_ida_init(struct percpu_ida *pool, unsigned long nr_tags,
e26b53d0 SL	287	unsigned long max_size, unsigned long batch_size)
798ab48e KO	288	{
	289	unsigned i, cpu, order;
	290
	291	memset(pool, 0, sizeof(*pool));
	292
	293	init_waitqueue_head(&pool->wait);
	294	spin_lock_init(&pool->lock);
	295	pool->nr_tags = nr_tags;
e26b53d0 SL	296	pool->percpu_max_size = max_size;
e26b53d0 SL	297	pool->percpu_batch_size = batch_size;
798ab48e KO	298
	299	/* Guard against overflow */
	300	if (nr_tags > (unsigned) INT_MAX + 1) {
	301	pr_err("percpu_ida_init(): nr_tags too large\n");
	302	return -EINVAL;
	303	}
	304
	305	order = get_order(nr_tags * sizeof(unsigned));
	306	pool->freelist = (void *) __get_free_pages(GFP_KERNEL, order);
	307	if (!pool->freelist)
	308	return -ENOMEM;
	309
	310	for (i = 0; i < nr_tags; i++)
	311	pool->freelist[i] = i;
	312
	313	pool->nr_free = nr_tags;
	314
	315	pool->tag_cpu = __alloc_percpu(sizeof(struct percpu_ida_cpu) +
e26b53d0	316	pool->percpu_max_size * sizeof(unsigned),
798ab48e KO	317	sizeof(unsigned));
	318	if (!pool->tag_cpu)
	319	goto err;
	320
	321	for_each_possible_cpu(cpu)
	322	spin_lock_init(&per_cpu_ptr(pool->tag_cpu, cpu)->lock);
	323
	324	return 0;
	325	err:
	326	percpu_ida_destroy(pool);
	327	return -ENOMEM;
	328	}
e26b53d0	329	EXPORT_SYMBOL_GPL(__percpu_ida_init);
7fc2ba17 SL	330
	331	/**
	332	* percpu_ida_for_each_free - iterate free ids of a pool
	333	* @pool: pool to iterate
	334	* @fn: interate callback function
	335	* @data: parameter for @fn
	336	*
	337	* Note, this doesn't guarantee to iterate all free ids restrictly. Some free
	338	* ids might be missed, some might be iterated duplicated, and some might
	339	* be iterated and not free soon.
	340	*/
	341	int percpu_ida_for_each_free(struct percpu_ida *pool, percpu_ida_cb fn,
	342	void *data)
	343	{
	344	unsigned long flags;
	345	struct percpu_ida_cpu *remote;
	346	unsigned cpu, i, err = 0;
	347
	348	local_irq_save(flags);
	349	for_each_possible_cpu(cpu) {
	350	remote = per_cpu_ptr(pool->tag_cpu, cpu);
	351	spin_lock(&remote->lock);
	352	for (i = 0; i < remote->nr_free; i++) {
	353	err = fn(remote->freelist[i], data);
	354	if (err)
	355	break;
	356	}
	357	spin_unlock(&remote->lock);
	358	if (err)
	359	goto out;
	360	}
	361
	362	spin_lock(&pool->lock);
	363	for (i = 0; i < pool->nr_free; i++) {
	364	err = fn(pool->freelist[i], data);
	365	if (err)
	366	break;
	367	}
	368	spin_unlock(&pool->lock);
	369	out:
	370	local_irq_restore(flags);
	371	return err;
	372	}
	373	EXPORT_SYMBOL_GPL(percpu_ida_for_each_free);
1dddc01a SL	374
	375	/**
	376	* percpu_ida_free_tags - return free tags number of a specific cpu or global pool
	377	* @pool: pool related
	378	* @cpu: specific cpu or global pool if @cpu == nr_cpu_ids
	379	*
	380	* Note: this just returns a snapshot of free tags number.
	381	*/
	382	unsigned percpu_ida_free_tags(struct percpu_ida *pool, int cpu)
	383	{
	384	struct percpu_ida_cpu *remote;
	385	if (cpu == nr_cpu_ids)
	386	return pool->nr_free;
	387	remote = per_cpu_ptr(pool->tag_cpu, cpu);
	388	return remote->nr_free;
	389	}
	390	EXPORT_SYMBOL_GPL(percpu_ida_free_tags);