idr: Percpu ida

#ifndef __PERCPU_IDA_H__

#define __PERCPU_IDA_H__

#include <linux/types.h>

#include <linux/bitops.h>

#include <linux/init.h>

#include <linux/spinlock_types.h>

#include <linux/wait.h>

#include <linux/cpumask.h>

struct percpu_ida_cpu;

struct percpu_ida {

	/*

	 * number of tags available to be allocated, as passed to

	 * percpu_ida_init()

	 */

	unsigned			nr_tags;

	struct percpu_ida_cpu __percpu	*tag_cpu;

	/*

	 * Bitmap of cpus that (may) have tags on their percpu freelists:

	 * steal_tags() uses this to decide when to steal tags, and which cpus

	 * to try stealing from.

	 *

	 * It's ok for a freelist to be empty when its bit is set - steal_tags()

	 * will just keep looking - but the bitmap _must_ be set whenever a

	 * percpu freelist does have tags.

	 */

	cpumask_t			cpus_have_tags;

	struct {

		spinlock_t		lock;

		/*

		 * When we go to steal tags from another cpu (see steal_tags()),

		 * we want to pick a cpu at random. Cycling through them every

		 * time we steal is a bit easier and more or less equivalent:

		 */

		unsigned		cpu_last_stolen;

		/* For sleeping on allocation failure */

		wait_queue_head_t	wait;

		/*

		 * Global freelist - it's a stack where nr_free points to the

		 * top

		 */

		unsigned		nr_free;

		unsigned		*freelist;

	} ____cacheline_aligned_in_smp;

};

int percpu_ida_alloc(struct percpu_ida *pool, gfp_t gfp);

void percpu_ida_free(struct percpu_ida *pool, unsigned tag);

void percpu_ida_destroy(struct percpu_ida *pool);

int percpu_ida_init(struct percpu_ida *pool, unsigned long nr_tags);

#endif /* __PERCPU_IDA_H__ */

	 sha1.o md5.o irq_regs.o reciprocal_div.o argv_split.o \

	 proportions.o flex_proportions.o prio_heap.o ratelimit.o show_mem.o \

	 is_single_threaded.o plist.o decompress.o kobject_uevent.o \

	 earlycpio.o percpu-refcount.o

	 earlycpio.o percpu-refcount.o percpu_ida.o

obj-$(CONFIG_ARCH_HAS_DEBUG_STRICT_USER_COPY_CHECKS) += usercopy.o

lib-$(CONFIG_MMU) += ioremap.o

obj-y += bcd.o div64.o sort.o parser.o halfmd4.o debug_locks.o random32.o \

	 bust_spinlocks.o hexdump.o kasprintf.o bitmap.o scatterlist.o \

	 gcd.o lcm.o list_sort.o uuid.o flex_array.o iovec.o clz_ctz.o \

	 bsearch.o find_last_bit.o find_next_bit.o llist.o memweight.o kfifo.o

	 bsearch.o find_last_bit.o find_next_bit.o llist.o memweight.o kfifo.o \

	 percpu_ida.o

obj-y += string_helpers.o

obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o

obj-y += kstrtox.o

/*

 * 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/hardirq.h>

#include <linux/idr.h>

#include <linux/init.h>

#include <linux/kernel.h>

#include <linux/percpu.h>

#include <linux/sched.h>

#include <linux/slab.h>

#include <linux/string.h>

#include <linux/spinlock.h>

#include <linux/percpu_ida.h>

/*

 * Number of tags we move between the percpu freelist and the global freelist at

 * a time

 */

#define IDA_PCPU_BATCH_MOVE	32U

/* Max size of percpu freelist, */

#define IDA_PCPU_SIZE		((IDA_PCPU_BATCH_MOVE * 3) / 2)

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 - we don't steal tags

 * unless enough percpu freelists have tags on them that it's possible more than

 * half the total tags could be stuck on remote percpu freelists.

 *

 * 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 * IDA_PCPU_SIZE > pool->nr_tags / 2;

	     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, IDA_PCPU_BATCH_MOVE));

}

static inline unsigned alloc_local_tag(struct percpu_ida *pool,

				       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

 * @gfp: gfp flags

 *

 * 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

 * __GFP_WAIT, 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_WAIT we may sleep

 * however long it takes until another thread frees an id (same semantics as a

 * mempool).

 *

 * Will not fail if passed __GFP_WAIT.

 */

int percpu_ida_alloc(struct percpu_ida *pool, gfp_t gfp)

{

	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(pool, 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

		 */

		prepare_to_wait(&pool->wait, &wait, TASK_UNINTERRUPTIBLE);

		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 || !(gfp & __GFP_WAIT))

			break;

		schedule();

		local_irq_save(flags);

		tags = this_cpu_ptr(pool->tag_cpu);

	}

	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 == IDA_PCPU_SIZE) {

		spin_lock(&pool->lock);

		/*

		 * Global lock held and irqs disabled, don't need percpu

		 * lock

		 */

		if (tags->nr_free == IDA_PCPU_SIZE) {

			move_tags(pool->freelist, &pool->nr_free,

				  tags->freelist, &tags->nr_free,

				  IDA_PCPU_BATCH_MOVE);

			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 i, cpu, order;

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

	init_waitqueue_head(&pool->wait);

	spin_lock_init(&pool->lock);

	pool->nr_tags = nr_tags;

	/* 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) +

				       IDA_PCPU_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);