/*
   *  linux/mm/mempool.c
   *
   *  memory buffer pool support. Such pools are mostly used
   *  for guaranteed, deadlock-free memory allocations during
   *  extreme VM load.
   *
   *  started by Ingo Molnar, Copyright (C) 2001
   */
  
  #include <linux/mm.h>
  #include <linux/slab.h>

  #include <linux/export.h>

  #include <linux/mempool.h>
  #include <linux/blkdev.h>
  #include <linux/writeback.h>
  
  static void add_element(mempool_t *pool, void *element)
  {
  	BUG_ON(pool->curr_nr >= pool->min_nr);
  	pool->elements[pool->curr_nr++] = element;
  }
  
  static void *remove_element(mempool_t *pool)
  {
  	BUG_ON(pool->curr_nr <= 0);
  	return pool->elements[--pool->curr_nr];
  }

  /**
   * mempool_destroy - deallocate a memory pool
   * @pool:      pointer to the memory pool which was allocated via
   *             mempool_create().
   *
   * Free all reserved elements in @pool and @pool itself.  This function
   * only sleeps if the free_fn() function sleeps.
   */
  void mempool_destroy(mempool_t *pool)

  {
  	while (pool->curr_nr) {
  		void *element = remove_element(pool);
  		pool->free(element, pool->pool_data);
  	}
  	kfree(pool->elements);
  	kfree(pool);
  }

  EXPORT_SYMBOL(mempool_destroy);

  
  /**
   * mempool_create - create a memory pool
   * @min_nr:    the minimum number of elements guaranteed to be
   *             allocated for this pool.
   * @alloc_fn:  user-defined element-allocation function.
   * @free_fn:   user-defined element-freeing function.
   * @pool_data: optional private data available to the user-defined functions.
   *
   * this function creates and allocates a guaranteed size, preallocated

   * memory pool. The pool can be used from the mempool_alloc() and mempool_free()

   * functions. This function might sleep. Both the alloc_fn() and the free_fn()

   * functions might sleep - as long as the mempool_alloc() function is not called

   * from IRQ contexts.
   */

  mempool_t *mempool_create(int min_nr, mempool_alloc_t *alloc_fn,

  				mempool_free_t *free_fn, void *pool_data)
  {

  	return  mempool_create_node(min_nr,alloc_fn,free_fn, pool_data,-1);
  }
  EXPORT_SYMBOL(mempool_create);

  mempool_t *mempool_create_node(int min_nr, mempool_alloc_t *alloc_fn,
  			mempool_free_t *free_fn, void *pool_data, int node_id)
  {
  	mempool_t *pool;

  	pool = kmalloc_node(sizeof(*pool), GFP_KERNEL | __GFP_ZERO, node_id);

  	if (!pool)
  		return NULL;

  	pool->elements = kmalloc_node(min_nr * sizeof(void *),
  					GFP_KERNEL, node_id);

  	if (!pool->elements) {
  		kfree(pool);
  		return NULL;
  	}
  	spin_lock_init(&pool->lock);
  	pool->min_nr = min_nr;
  	pool->pool_data = pool_data;
  	init_waitqueue_head(&pool->wait);
  	pool->alloc = alloc_fn;
  	pool->free = free_fn;
  
  	/*
  	 * First pre-allocate the guaranteed number of buffers.
  	 */
  	while (pool->curr_nr < pool->min_nr) {
  		void *element;
  
  		element = pool->alloc(GFP_KERNEL, pool->pool_data);
  		if (unlikely(!element)) {

  			mempool_destroy(pool);

  			return NULL;
  		}
  		add_element(pool, element);
  	}
  	return pool;
  }

  EXPORT_SYMBOL(mempool_create_node);

  
  /**
   * mempool_resize - resize an existing memory pool
   * @pool:       pointer to the memory pool which was allocated via
   *              mempool_create().
   * @new_min_nr: the new minimum number of elements guaranteed to be
   *              allocated for this pool.
   * @gfp_mask:   the usual allocation bitmask.
   *
   * This function shrinks/grows the pool. In the case of growing,
   * it cannot be guaranteed that the pool will be grown to the new
   * size immediately, but new mempool_free() calls will refill it.
   *
   * Note, the caller must guarantee that no mempool_destroy is called
   * while this function is running. mempool_alloc() & mempool_free()
   * might be called (eg. from IRQ contexts) while this function executes.
   */

  int mempool_resize(mempool_t *pool, int new_min_nr, gfp_t gfp_mask)

  {
  	void *element;
  	void **new_elements;
  	unsigned long flags;
  
  	BUG_ON(new_min_nr <= 0);
  
  	spin_lock_irqsave(&pool->lock, flags);
  	if (new_min_nr <= pool->min_nr) {
  		while (new_min_nr < pool->curr_nr) {
  			element = remove_element(pool);
  			spin_unlock_irqrestore(&pool->lock, flags);
  			pool->free(element, pool->pool_data);
  			spin_lock_irqsave(&pool->lock, flags);
  		}
  		pool->min_nr = new_min_nr;
  		goto out_unlock;
  	}
  	spin_unlock_irqrestore(&pool->lock, flags);
  
  	/* Grow the pool */
  	new_elements = kmalloc(new_min_nr * sizeof(*new_elements), gfp_mask);
  	if (!new_elements)
  		return -ENOMEM;
  
  	spin_lock_irqsave(&pool->lock, flags);
  	if (unlikely(new_min_nr <= pool->min_nr)) {
  		/* Raced, other resize will do our work */
  		spin_unlock_irqrestore(&pool->lock, flags);
  		kfree(new_elements);
  		goto out;
  	}
  	memcpy(new_elements, pool->elements,
  			pool->curr_nr * sizeof(*new_elements));
  	kfree(pool->elements);
  	pool->elements = new_elements;
  	pool->min_nr = new_min_nr;
  
  	while (pool->curr_nr < pool->min_nr) {
  		spin_unlock_irqrestore(&pool->lock, flags);
  		element = pool->alloc(gfp_mask, pool->pool_data);
  		if (!element)
  			goto out;
  		spin_lock_irqsave(&pool->lock, flags);
  		if (pool->curr_nr < pool->min_nr) {
  			add_element(pool, element);
  		} else {
  			spin_unlock_irqrestore(&pool->lock, flags);
  			pool->free(element, pool->pool_data);	/* Raced */
  			goto out;
  		}
  	}
  out_unlock:
  	spin_unlock_irqrestore(&pool->lock, flags);
  out:
  	return 0;
  }
  EXPORT_SYMBOL(mempool_resize);
  
  /**

   * mempool_alloc - allocate an element from a specific memory pool
   * @pool:      pointer to the memory pool which was allocated via
   *             mempool_create().
   * @gfp_mask:  the usual allocation bitmask.
   *

   * this function only sleeps if the alloc_fn() function sleeps or

   * returns NULL. Note that due to preallocation, this function
   * *never* fails when called from process contexts. (it might
   * fail if called from an IRQ context.)
   */

  void * mempool_alloc(mempool_t *pool, gfp_t gfp_mask)

  {
  	void *element;
  	unsigned long flags;

  	wait_queue_t wait;

  	gfp_t gfp_temp;

  
  	might_sleep_if(gfp_mask & __GFP_WAIT);

  
  	gfp_mask |= __GFP_NOMEMALLOC;	/* don't allocate emergency reserves */
  	gfp_mask |= __GFP_NORETRY;	/* don't loop in __alloc_pages */
  	gfp_mask |= __GFP_NOWARN;	/* failures are OK */

  	gfp_temp = gfp_mask & ~(__GFP_WAIT|__GFP_IO);

  repeat_alloc:

  
  	element = pool->alloc(gfp_temp, pool->pool_data);

  	if (likely(element != NULL))
  		return element;

  	spin_lock_irqsave(&pool->lock, flags);
  	if (likely(pool->curr_nr)) {
  		element = remove_element(pool);
  		spin_unlock_irqrestore(&pool->lock, flags);

  		/* paired with rmb in mempool_free(), read comment there */
  		smp_wmb();

  		return element;
  	}

  	/*
  	 * We use gfp mask w/o __GFP_WAIT or IO for the first round.  If
  	 * alloc failed with that and @pool was empty, retry immediately.
  	 */
  	if (gfp_temp != gfp_mask) {
  		spin_unlock_irqrestore(&pool->lock, flags);
  		gfp_temp = gfp_mask;
  		goto repeat_alloc;
  	}
  
  	/* We must not sleep if !__GFP_WAIT */

  	if (!(gfp_mask & __GFP_WAIT)) {
  		spin_unlock_irqrestore(&pool->lock, flags);

  		return NULL;

  	}

  	/* Let's wait for someone else to return an element to @pool */

  	init_wait(&wait);

  	prepare_to_wait(&pool->wait, &wait, TASK_UNINTERRUPTIBLE);

  	spin_unlock_irqrestore(&pool->lock, flags);
  
  	/*
  	 * FIXME: this should be io_schedule().  The timeout is there as a
  	 * workaround for some DM problems in 2.6.18.
  	 */
  	io_schedule_timeout(5*HZ);
  
  	finish_wait(&pool->wait, &wait);

  	goto repeat_alloc;
  }
  EXPORT_SYMBOL(mempool_alloc);
  
  /**
   * mempool_free - return an element to the pool.
   * @element:   pool element pointer.
   * @pool:      pointer to the memory pool which was allocated via
   *             mempool_create().
   *
   * this function only sleeps if the free_fn() function sleeps.
   */
  void mempool_free(void *element, mempool_t *pool)
  {
  	unsigned long flags;

  	if (unlikely(element == NULL))
  		return;

  	/*
  	 * Paired with the wmb in mempool_alloc().  The preceding read is
  	 * for @element and the following @pool->curr_nr.  This ensures
  	 * that the visible value of @pool->curr_nr is from after the
  	 * allocation of @element.  This is necessary for fringe cases
  	 * where @element was passed to this task without going through
  	 * barriers.
  	 *
  	 * For example, assume @p is %NULL at the beginning and one task
  	 * performs "p = mempool_alloc(...);" while another task is doing
  	 * "while (!p) cpu_relax(); mempool_free(p, ...);".  This function
  	 * may end up using curr_nr value which is from before allocation
  	 * of @p without the following rmb.
  	 */
  	smp_rmb();
  
  	/*
  	 * For correctness, we need a test which is guaranteed to trigger
  	 * if curr_nr + #allocated == min_nr.  Testing curr_nr < min_nr
  	 * without locking achieves that and refilling as soon as possible
  	 * is desirable.
  	 *
  	 * Because curr_nr visible here is always a value after the
  	 * allocation of @element, any task which decremented curr_nr below
  	 * min_nr is guaranteed to see curr_nr < min_nr unless curr_nr gets
  	 * incremented to min_nr afterwards.  If curr_nr gets incremented
  	 * to min_nr after the allocation of @element, the elements
  	 * allocated after that are subject to the same guarantee.
  	 *
  	 * Waiters happen iff curr_nr is 0 and the above guarantee also
  	 * ensures that there will be frees which return elements to the
  	 * pool waking up the waiters.
  	 */

  	if (pool->curr_nr < pool->min_nr) {
  		spin_lock_irqsave(&pool->lock, flags);
  		if (pool->curr_nr < pool->min_nr) {
  			add_element(pool, element);
  			spin_unlock_irqrestore(&pool->lock, flags);
  			wake_up(&pool->wait);
  			return;
  		}
  		spin_unlock_irqrestore(&pool->lock, flags);
  	}
  	pool->free(element, pool->pool_data);
  }
  EXPORT_SYMBOL(mempool_free);
  
  /*
   * A commonly used alloc and free fn.
   */

  void *mempool_alloc_slab(gfp_t gfp_mask, void *pool_data)

  {

  	struct kmem_cache *mem = pool_data;

  	return kmem_cache_alloc(mem, gfp_mask);
  }
  EXPORT_SYMBOL(mempool_alloc_slab);
  
  void mempool_free_slab(void *element, void *pool_data)
  {

  	struct kmem_cache *mem = pool_data;

  	kmem_cache_free(mem, element);
  }
  EXPORT_SYMBOL(mempool_free_slab);

  
  /*

   * A commonly used alloc and free fn that kmalloc/kfrees the amount of memory

   * specified by pool_data

   */
  void *mempool_kmalloc(gfp_t gfp_mask, void *pool_data)
  {

  	size_t size = (size_t)pool_data;

  	return kmalloc(size, gfp_mask);
  }
  EXPORT_SYMBOL(mempool_kmalloc);
  
  void mempool_kfree(void *element, void *pool_data)
  {
  	kfree(element);
  }
  EXPORT_SYMBOL(mempool_kfree);
  
  /*

   * A simple mempool-backed page allocator that allocates pages
   * of the order specified by pool_data.
   */
  void *mempool_alloc_pages(gfp_t gfp_mask, void *pool_data)
  {
  	int order = (int)(long)pool_data;
  	return alloc_pages(gfp_mask, order);
  }
  EXPORT_SYMBOL(mempool_alloc_pages);
  
  void mempool_free_pages(void *element, void *pool_data)
  {
  	int order = (int)(long)pool_data;
  	__free_pages(element, order);
  }
  EXPORT_SYMBOL(mempool_free_pages);