kern/include/percpu_counter.h

/* Copyright (C) 1991-2017, the Linux Kernel authors */

#ifndef _LINUX_PERCPU_COUNTER_H
#define _LINUX_PERCPU_COUNTER_H
/*
 * A simple "approximate counter".
 */

#include <atomic.h>
#include <list.h>

struct percpu_counter {
	spinlock_t lock;
	int64_t count;
#ifdef CONFIG_HOTPLUG_CPU
	struct list_head list;	/* All percpu_counters are on a list */
#endif
	int32_t *counters;
};

extern int percpu_counter_batch;

int percpu_counter_init(struct percpu_counter *fbc, int64_t amount, int gfp);
void percpu_counter_destroy(struct percpu_counter *fbc);
void percpu_counter_set(struct percpu_counter *fbc, int64_t amount);
void percpu_counter_add_batch(struct percpu_counter *fbc, int64_t amount,
			      int32_t batch);
int64_t __percpu_counter_sum(struct percpu_counter *fbc);
int __percpu_counter_compare(struct percpu_counter *fbc, int64_t rhs,
			     int32_t batch);

static inline int percpu_counter_compare(struct percpu_counter *fbc,
					 int64_t rhs)
{
	return __percpu_counter_compare(fbc, rhs, percpu_counter_batch);
}

static inline void percpu_counter_add(struct percpu_counter *fbc,
				      int64_t amount)
{
	percpu_counter_add_batch(fbc, amount, percpu_counter_batch);
}

static inline int64_t percpu_counter_sum_positive(struct percpu_counter *fbc)
{
	int64_t ret = __percpu_counter_sum(fbc);
	return ret < 0 ? 0 : ret;
}

static inline int64_t percpu_counter_sum(struct percpu_counter *fbc)
{
	return __percpu_counter_sum(fbc);
}

static inline int64_t percpu_counter_read(struct percpu_counter *fbc)
{
	return fbc->count;
}

/*
 * It is possible for the percpu_counter_read() to return a small negative
 * number for some counter which should never be negative.
 *
 */
static inline int64_t percpu_counter_read_positive(struct percpu_counter *fbc)
{
	int64_t ret = fbc->count;

	cmb();		/* Prevent reloads of fbc->count */
	if (ret >= 0)
		return ret;
	return 0;
}

static inline int percpu_counter_initialized(struct percpu_counter *fbc)
{
	return (fbc->counters != NULL);
}

static inline void percpu_counter_inc(struct percpu_counter *fbc)
{
	percpu_counter_add(fbc, 1);
}

static inline void percpu_counter_dec(struct percpu_counter *fbc)
{
	percpu_counter_add(fbc, -1);
}

static inline void percpu_counter_sub(struct percpu_counter *fbc,
				      int64_t amount)
{
	percpu_counter_add(fbc, -amount);
}

#endif /* _LINUX_PERCPU_COUNTER_H */