#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 *counters;

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

  void percpu_counter_init(struct percpu_counter *fbc, s64 amount);
  void percpu_counter_destroy(struct percpu_counter *fbc);

  void percpu_counter_mod(struct percpu_counter *fbc, s32 amount);
  s64 percpu_counter_sum(struct percpu_counter *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 void percpu_counter_init(struct percpu_counter *fbc, s64 amount)

  {

  	fbc->count = amount;

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

  percpu_counter_mod(struct percpu_counter *fbc, s32 amount)

  {
  	preempt_disable();
  	fbc->count += amount;
  	preempt_enable();
  }

  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(struct percpu_counter *fbc)

  {
  	return percpu_counter_read_positive(fbc);
  }

  #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);
  }
  
  #endif /* _LINUX_PERCPU_COUNTER_H */