struct percpu_counter {
	atomic_long_t count;
	atomic_long_t *counters;
};

#ifdef CONFIG_SMP
void percpu_counter_mod(struct percpu_counter *fbc, long amount)
{
	long old, new;
	atomic_long_t *pcount;

	pcount = per_cpu_ptr(fbc->counters, get_cpu());
start:
	old = atomic_long_read(pcount);
	new = old + amount;
	if (new >= FBC_BATCH || new <= -FBC_BATCH) {
		if (unlikely(atomic_long_cmpxchg(pcount, old, 0) != old))
			goto start;
		atomic_long_add(new, &fbc->count);
	} else
		atomic_long_add(amount, pcount);

	put_cpu();
}
EXPORT_SYMBOL(percpu_counter_mod);

long percpu_counter_read_accurate(struct percpu_counter *fbc)
{
	long res = 0;
	int cpu;
	atomic_long_t *pcount;

	for_each_cpu(cpu) {
		pcount = per_cpu_ptr(fbc->counters, cpu);
		/* dont dirty cache line if not necessary */
		if (atomic_long_read(pcount))
			res += atomic_long_xchg(pcount, 0);
	}
	return res;
}
EXPORT_SYMBOL(percpu_counter_read_accurate);
#endif /* CONFIG_SMP */