#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 {
  	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 1;
  }
  
  #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;
  }

  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);
  }

  #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 */