percpu_counter.h

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#ifndef _LINUX_PERCPU_COUNTER_H
#define _LINUX_PERCPU_COUNTER_H
/*
 * A simple "approximate counter" for use in ext2 and ext3 superblocks.
 *
 * WARNING: these things are HUGE.  4 kbytes per counter on 32-way P4.
 */

#include <linux/spinlock.h>
#include <linux/smp.h>
#include <linux/list.h>
#include <linux/threads.h>
#include <linux/percpu.h>
#include <linux/types.h>

#ifdef CONFIG_SMP

struct percpu_counter {
    raw_spinlock_t lock;
    s64 count;
#ifdef CONFIG_HOTPLUG_CPU
    struct list_head list;  /* All percpu_counters are on a list */
#endif
    s32 __percpu *counters;
};

extern int percpu_counter_batch;

int __percpu_counter_init(struct percpu_counter *fbc, s64 amount,
              struct lock_class_key *key);

#define percpu_counter_init(fbc, value)                 \
    ({                              \
        static struct lock_class_key __key;         \
                                    \
        __percpu_counter_init(fbc, value, &__key);      \
    })

void percpu_counter_destroy(struct percpu_counter *fbc);
void percpu_counter_set(struct percpu_counter *fbc, s64 amount);
void __percpu_counter_add(struct percpu_counter *fbc, s64 amount, s32 batch);
s64 __percpu_counter_sum(struct percpu_counter *fbc);
int percpu_counter_compare(struct percpu_counter *fbc, s64 rhs);

static inline void percpu_counter_add(struct percpu_counter *fbc, s64 amount)
{
    __percpu_counter_add(fbc, amount, percpu_counter_batch);
}

static inline s64 percpu_counter_sum_positive(struct percpu_counter *fbc)
{
    s64 ret = __percpu_counter_sum(fbc);
    return ret < 0 ? 0 : ret;
}

static inline s64 percpu_counter_sum(struct percpu_counter *fbc)
{
    return __percpu_counter_sum(fbc);
}

static inline s64 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 s64 percpu_counter_read_positive(struct percpu_counter *fbc)
{
    s64 ret = fbc->count;

    barrier();      /* 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);
}

#else

struct percpu_counter {
    s64 count;
};

static inline int percpu_counter_init(struct percpu_counter *fbc, s64 amount)
{
    fbc->count = amount;
    return 0;
}

static inline void percpu_counter_destroy(struct percpu_counter *fbc)
{
}

static inline void percpu_counter_set(struct percpu_counter *fbc, s64 amount)
{
    fbc->count = amount;
}

static inline int percpu_counter_compare(struct percpu_counter *fbc, s64 rhs)
{
    if (fbc->count > rhs)
        return 1;
    else if (fbc->count < rhs)
        return -1;
    else
        return 0;
}

static inline void
percpu_counter_add(struct percpu_counter *fbc, s64 amount)
{
    preempt_disable();
    fbc->count += amount;
    preempt_enable();
}

static inline void
__percpu_counter_add(struct percpu_counter *fbc, s64 amount, s32 batch)
{
    percpu_counter_add(fbc, amount);
}

static inline s64 percpu_counter_read(struct percpu_counter *fbc)
{
    return fbc->count;
}

/*
 * percpu_counter is intended to track positive numbers. In the UP case the
 * number should never be negative.
 */
static inline s64 percpu_counter_read_positive(struct percpu_counter *fbc)
{
    return fbc->count;
}

static inline s64 percpu_counter_sum_positive(struct percpu_counter *fbc)
{
    return percpu_counter_read_positive(fbc);
}

static inline s64 percpu_counter_sum(struct percpu_counter *fbc)
{
    return percpu_counter_read(fbc);
}

static inline int percpu_counter_initialized(struct percpu_counter *fbc)
{
    return 1;
}

#endif  /* CONFIG_SMP */

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, s64 amount)
{
    percpu_counter_add(fbc, -amount);
}

#endif /* _LINUX_PERCPU_COUNTER_H */