#ifndef __PERCPU_IDA_H__
  #define __PERCPU_IDA_H__
  
  #include <linux/types.h>
  #include <linux/bitops.h>
  #include <linux/init.h>
  #include <linux/sched.h>
  #include <linux/spinlock_types.h>
  #include <linux/wait.h>
  #include <linux/cpumask.h>
  
  struct percpu_ida_cpu;
  
  struct percpu_ida {
  	/*
  	 * number of tags available to be allocated, as passed to
  	 * percpu_ida_init()
  	 */
  	unsigned			nr_tags;
  	unsigned			percpu_max_size;
  	unsigned			percpu_batch_size;
  
  	struct percpu_ida_cpu __percpu	*tag_cpu;
  
  	/*
  	 * Bitmap of cpus that (may) have tags on their percpu freelists:
  	 * steal_tags() uses this to decide when to steal tags, and which cpus
  	 * to try stealing from.
  	 *
  	 * It's ok for a freelist to be empty when its bit is set - steal_tags()
  	 * will just keep looking - but the bitmap _must_ be set whenever a
  	 * percpu freelist does have tags.
  	 */
  	cpumask_t			cpus_have_tags;
  
  	struct {
  		spinlock_t		lock;
  		/*
  		 * When we go to steal tags from another cpu (see steal_tags()),
  		 * we want to pick a cpu at random. Cycling through them every
  		 * time we steal is a bit easier and more or less equivalent:
  		 */
  		unsigned		cpu_last_stolen;
  
  		/* For sleeping on allocation failure */
  		wait_queue_head_t	wait;
  
  		/*
  		 * Global freelist - it's a stack where nr_free points to the
  		 * top
  		 */
  		unsigned		nr_free;
  		unsigned		*freelist;
  	} ____cacheline_aligned_in_smp;
  };
  
  /*
   * Number of tags we move between the percpu freelist and the global freelist at
   * a time
   */
  #define IDA_DEFAULT_PCPU_BATCH_MOVE	32U
  /* Max size of percpu freelist, */
  #define IDA_DEFAULT_PCPU_SIZE	((IDA_DEFAULT_PCPU_BATCH_MOVE * 3) / 2)
  
  int percpu_ida_alloc(struct percpu_ida *pool, int state);
  void percpu_ida_free(struct percpu_ida *pool, unsigned tag);
  
  void percpu_ida_destroy(struct percpu_ida *pool);
  int __percpu_ida_init(struct percpu_ida *pool, unsigned long nr_tags,
  	unsigned long max_size, unsigned long batch_size);
  static inline int percpu_ida_init(struct percpu_ida *pool, unsigned long nr_tags)
  {
  	return __percpu_ida_init(pool, nr_tags, IDA_DEFAULT_PCPU_SIZE,
  		IDA_DEFAULT_PCPU_BATCH_MOVE);
  }
  
  typedef int (*percpu_ida_cb)(unsigned, void *);
  int percpu_ida_for_each_free(struct percpu_ida *pool, percpu_ida_cb fn,
  	void *data);
  
  unsigned percpu_ida_free_tags(struct percpu_ida *pool, int cpu);
  #endif /* __PERCPU_IDA_H__ */