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/*
 * 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/config.h>
#include <linux/spinlock.h>
#include <linux/smp.h>
#include <linux/threads.h>

#ifdef CONFIG_SMP

struct __percpu_counter {
        long count;
} ____cacheline_aligned;

struct percpu_counter {
        spinlock_t lock;
        long count;
        struct __percpu_counter counters[NR_CPUS];
};

#if NR_CPUS >= 16
#define FBC_BATCH       (NR_CPUS*2)
#else
#define FBC_BATCH       (NR_CPUS*4)
#endif

static inline void percpu_counter_init(struct percpu_counter *fbc)
{
        int i;

        spin_lock_init(&fbc->lock);
        fbc->count = 0;
        for (i = 0; i < NR_CPUS; i++)
                fbc->counters[i].count = 0;
}

void percpu_counter_mod(struct percpu_counter *fbc, long amount);

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

        barrier();              /* Prevent reloads of fbc->count */
        if (ret > 0)
                return ret;
        return 1;
}

#else

struct percpu_counter {
        long count;
};

static inline void percpu_counter_init(struct percpu_counter *fbc)
{
        fbc->count = 0;
}

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

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

static inline long percpu_counter_read_positive(struct percpu_counter *fbc)
{
        return fbc->count;
}

#endif  /* CONFIG_SMP */

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

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