#include <linux/swap_cgroup.h>

  #include <linux/vmalloc.h>

  #include <linux/mm.h>

  #include <linux/swapops.h> /* depends on mm.h include */

  
  static DEFINE_MUTEX(swap_cgroup_mutex);
  struct swap_cgroup_ctrl {
  	struct page **map;
  	unsigned long length;

  	spinlock_t	lock;

  };

  static struct swap_cgroup_ctrl swap_cgroup_ctrl[MAX_SWAPFILES];

  struct swap_cgroup {

  	unsigned short		id;

  };
  #define SC_PER_PAGE	(PAGE_SIZE/sizeof(struct swap_cgroup))

  
  /*
   * SwapCgroup implements "lookup" and "exchange" operations.
   * In typical usage, this swap_cgroup is accessed via memcg's charge/uncharge
   * against SwapCache. At swap_free(), this is accessed directly from swap.
   *
   * This means,
   *  - we have no race in "exchange" when we're accessed via SwapCache because
   *    SwapCache(and its swp_entry) is under lock.
   *  - When called via swap_free(), there is no user of this entry and no race.
   * Then, we don't need lock around "exchange".
   *
   * TODO: we can push these buffers out to HIGHMEM.
   */
  
  /*
   * allocate buffer for swap_cgroup.
   */
  static int swap_cgroup_prepare(int type)
  {
  	struct page *page;
  	struct swap_cgroup_ctrl *ctrl;
  	unsigned long idx, max;

  	ctrl = &swap_cgroup_ctrl[type];
  
  	for (idx = 0; idx < ctrl->length; idx++) {
  		page = alloc_page(GFP_KERNEL | __GFP_ZERO);
  		if (!page)
  			goto not_enough_page;
  		ctrl->map[idx] = page;
  	}
  	return 0;
  not_enough_page:
  	max = idx;
  	for (idx = 0; idx < max; idx++)
  		__free_page(ctrl->map[idx]);
  
  	return -ENOMEM;
  }

  static struct swap_cgroup *lookup_swap_cgroup(swp_entry_t ent,
  					struct swap_cgroup_ctrl **ctrlp)
  {
  	pgoff_t offset = swp_offset(ent);
  	struct swap_cgroup_ctrl *ctrl;
  	struct page *mappage;

  	struct swap_cgroup *sc;

  
  	ctrl = &swap_cgroup_ctrl[swp_type(ent)];
  	if (ctrlp)
  		*ctrlp = ctrl;
  
  	mappage = ctrl->map[offset / SC_PER_PAGE];

  	sc = page_address(mappage);
  	return sc + offset % SC_PER_PAGE;

  }

  /**

   * swap_cgroup_cmpxchg - cmpxchg mem_cgroup's id for this swp_entry.

   * @ent: swap entry to be cmpxchged

   * @old: old id
   * @new: new id
   *
   * Returns old id at success, 0 at failure.

   * (There is no mem_cgroup using 0 as its id)

   */
  unsigned short swap_cgroup_cmpxchg(swp_entry_t ent,
  					unsigned short old, unsigned short new)
  {

  	struct swap_cgroup_ctrl *ctrl;

  	struct swap_cgroup *sc;

  	unsigned long flags;
  	unsigned short retval;

  	sc = lookup_swap_cgroup(ent, &ctrl);

  	spin_lock_irqsave(&ctrl->lock, flags);
  	retval = sc->id;
  	if (retval == old)
  		sc->id = new;

  	else

  		retval = 0;
  	spin_unlock_irqrestore(&ctrl->lock, flags);
  	return retval;

  }
  
  /**

   * swap_cgroup_record - record mem_cgroup for this swp_entry.
   * @ent: swap entry to be recorded into

   * @id: mem_cgroup to be recorded

   *

   * Returns old value at success, 0 at failure.
   * (Of course, old value can be 0.)

   */

  unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id)

  {

  	struct swap_cgroup_ctrl *ctrl;

  	struct swap_cgroup *sc;

  	unsigned short old;

  	unsigned long flags;

  	sc = lookup_swap_cgroup(ent, &ctrl);

  	spin_lock_irqsave(&ctrl->lock, flags);
  	old = sc->id;
  	sc->id = id;
  	spin_unlock_irqrestore(&ctrl->lock, flags);

  
  	return old;
  }
  
  /**

   * lookup_swap_cgroup_id - lookup mem_cgroup id tied to swap entry

   * @ent: swap entry to be looked up.
   *

   * Returns ID of mem_cgroup at success. 0 at failure. (0 is invalid ID)

   */

  unsigned short lookup_swap_cgroup_id(swp_entry_t ent)

  {

  	return lookup_swap_cgroup(ent, NULL)->id;

  }
  
  int swap_cgroup_swapon(int type, unsigned long max_pages)
  {
  	void *array;
  	unsigned long array_size;
  	unsigned long length;
  	struct swap_cgroup_ctrl *ctrl;
  
  	if (!do_swap_account)
  		return 0;

  	length = DIV_ROUND_UP(max_pages, SC_PER_PAGE);

  	array_size = length * sizeof(void *);

  	array = vzalloc(array_size);

  	if (!array)
  		goto nomem;

  	ctrl = &swap_cgroup_ctrl[type];
  	mutex_lock(&swap_cgroup_mutex);
  	ctrl->length = length;
  	ctrl->map = array;

  	spin_lock_init(&ctrl->lock);

  	if (swap_cgroup_prepare(type)) {
  		/* memory shortage */
  		ctrl->map = NULL;
  		ctrl->length = 0;

  		mutex_unlock(&swap_cgroup_mutex);

  		vfree(array);

  		goto nomem;
  	}
  	mutex_unlock(&swap_cgroup_mutex);

  	return 0;
  nomem:

  	pr_info("couldn't allocate enough memory for swap_cgroup
  ");
  	pr_info("swap_cgroup can be disabled by swapaccount=0 boot option
  ");

  	return -ENOMEM;
  }
  
  void swap_cgroup_swapoff(int type)
  {

  	struct page **map;
  	unsigned long i, length;

  	struct swap_cgroup_ctrl *ctrl;
  
  	if (!do_swap_account)
  		return;
  
  	mutex_lock(&swap_cgroup_mutex);
  	ctrl = &swap_cgroup_ctrl[type];

  	map = ctrl->map;
  	length = ctrl->length;
  	ctrl->map = NULL;
  	ctrl->length = 0;
  	mutex_unlock(&swap_cgroup_mutex);
  
  	if (map) {
  		for (i = 0; i < length; i++) {
  			struct page *page = map[i];

  			if (page)
  				__free_page(page);
  		}

  		vfree(map);

  	}

  }