/*
   *  linux/mm/swapfile.c
   *
   *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
   *  Swap reorganised 29.12.95, Stephen Tweedie
   */

  #include <linux/mm.h>
  #include <linux/hugetlb.h>
  #include <linux/mman.h>
  #include <linux/slab.h>
  #include <linux/kernel_stat.h>
  #include <linux/swap.h>
  #include <linux/vmalloc.h>
  #include <linux/pagemap.h>
  #include <linux/namei.h>
  #include <linux/shm.h>
  #include <linux/blkdev.h>
  #include <linux/writeback.h>
  #include <linux/proc_fs.h>
  #include <linux/seq_file.h>
  #include <linux/init.h>
  #include <linux/module.h>
  #include <linux/rmap.h>
  #include <linux/security.h>
  #include <linux/backing-dev.h>

  #include <linux/mutex.h>

  #include <linux/capability.h>

  #include <linux/syscalls.h>

  #include <linux/memcontrol.h>

  
  #include <asm/pgtable.h>
  #include <asm/tlbflush.h>
  #include <linux/swapops.h>

  static DEFINE_SPINLOCK(swap_lock);
  static unsigned int nr_swapfiles;

  long total_swap_pages;
  static int swap_overflow;

  static int least_priority;

  static const char Bad_file[] = "Bad swap file entry ";
  static const char Unused_file[] = "Unused swap file entry ";
  static const char Bad_offset[] = "Bad swap offset entry ";
  static const char Unused_offset[] = "Unused swap offset entry ";

  static struct swap_list_t swap_list = {-1, -1};

  static struct swap_info_struct swap_info[MAX_SWAPFILES];

  static DEFINE_MUTEX(swapon_mutex);

  
  /*
   * We need this because the bdev->unplug_fn can sleep and we cannot

   * hold swap_lock while calling the unplug_fn. And swap_lock

   * cannot be turned into a mutex.

   */
  static DECLARE_RWSEM(swap_unplug_sem);

  void swap_unplug_io_fn(struct backing_dev_info *unused_bdi, struct page *page)
  {
  	swp_entry_t entry;
  
  	down_read(&swap_unplug_sem);

  	entry.val = page_private(page);

  	if (PageSwapCache(page)) {
  		struct block_device *bdev = swap_info[swp_type(entry)].bdev;
  		struct backing_dev_info *bdi;
  
  		/*
  		 * If the page is removed from swapcache from under us (with a
  		 * racy try_to_unuse/swapoff) we need an additional reference

  		 * count to avoid reading garbage from page_private(page) above.
  		 * If the WARN_ON triggers during a swapoff it maybe the race

  		 * condition and it's harmless. However if it triggers without
  		 * swapoff it signals a problem.
  		 */
  		WARN_ON(page_count(page) <= 1);
  
  		bdi = bdev->bd_inode->i_mapping->backing_dev_info;

  		blk_run_backing_dev(bdi, page);

  	}
  	up_read(&swap_unplug_sem);
  }

  #define SWAPFILE_CLUSTER	256
  #define LATENCY_LIMIT		256

  static inline unsigned long scan_swap_map(struct swap_info_struct *si)

  {

  	unsigned long offset, last_in_cluster;

  	int latency_ration = LATENCY_LIMIT;

  	/* 

  	 * We try to cluster swap pages by allocating them sequentially
  	 * in swap.  Once we've allocated SWAPFILE_CLUSTER pages this
  	 * way, however, we resort to first-free allocation, starting
  	 * a new cluster.  This prevents us from scattering swap pages
  	 * all over the entire swap partition, so that we reduce
  	 * overall disk seek times between swap pages.  -- sct
  	 * But we do now try to find an empty cluster.  -Andrea
  	 */

  	si->flags += SWP_SCANNING;

  	if (unlikely(!si->cluster_nr)) {
  		si->cluster_nr = SWAPFILE_CLUSTER - 1;
  		if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER)
  			goto lowest;

  		spin_unlock(&swap_lock);

  
  		offset = si->lowest_bit;
  		last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
  
  		/* Locate the first empty (unaligned) cluster */
  		for (; last_in_cluster <= si->highest_bit; offset++) {

  			if (si->swap_map[offset])

  				last_in_cluster = offset + SWAPFILE_CLUSTER;
  			else if (offset == last_in_cluster) {

  				spin_lock(&swap_lock);

  				si->cluster_next = offset-SWAPFILE_CLUSTER+1;

  				goto cluster;

  			}

  			if (unlikely(--latency_ration < 0)) {
  				cond_resched();
  				latency_ration = LATENCY_LIMIT;
  			}

  		}

  		spin_lock(&swap_lock);

  		goto lowest;

  	}

  
  	si->cluster_nr--;
  cluster:
  	offset = si->cluster_next;
  	if (offset > si->highest_bit)
  lowest:		offset = si->lowest_bit;

  checks:	if (!(si->flags & SWP_WRITEOK))
  		goto no_page;

  	if (!si->highest_bit)
  		goto no_page;
  	if (!si->swap_map[offset]) {

  		if (offset == si->lowest_bit)

  			si->lowest_bit++;
  		if (offset == si->highest_bit)
  			si->highest_bit--;

  		si->inuse_pages++;
  		if (si->inuse_pages == si->pages) {

  			si->lowest_bit = si->max;
  			si->highest_bit = 0;
  		}
  		si->swap_map[offset] = 1;

  		si->cluster_next = offset + 1;

  		si->flags -= SWP_SCANNING;

  		return offset;
  	}

  	spin_unlock(&swap_lock);

  	while (++offset <= si->highest_bit) {

  		if (!si->swap_map[offset]) {

  			spin_lock(&swap_lock);

  			goto checks;
  		}

  		if (unlikely(--latency_ration < 0)) {
  			cond_resched();
  			latency_ration = LATENCY_LIMIT;
  		}

  	}

  	spin_lock(&swap_lock);

  	goto lowest;
  
  no_page:

  	si->flags -= SWP_SCANNING;

  	return 0;
  }
  
  swp_entry_t get_swap_page(void)
  {

  	struct swap_info_struct *si;
  	pgoff_t offset;
  	int type, next;
  	int wrapped = 0;

  	spin_lock(&swap_lock);

  	if (nr_swap_pages <= 0)

  		goto noswap;
  	nr_swap_pages--;
  
  	for (type = swap_list.next; type >= 0 && wrapped < 2; type = next) {
  		si = swap_info + type;
  		next = si->next;
  		if (next < 0 ||
  		    (!wrapped && si->prio != swap_info[next].prio)) {
  			next = swap_list.head;
  			wrapped++;

  		}

  
  		if (!si->highest_bit)
  			continue;
  		if (!(si->flags & SWP_WRITEOK))
  			continue;
  
  		swap_list.next = next;

  		offset = scan_swap_map(si);

  		if (offset) {
  			spin_unlock(&swap_lock);

  			return swp_entry(type, offset);

  		}

  		next = swap_list.next;

  	}

  
  	nr_swap_pages++;
  noswap:

  	spin_unlock(&swap_lock);

  	return (swp_entry_t) {0};

  }

  swp_entry_t get_swap_page_of_type(int type)
  {
  	struct swap_info_struct *si;
  	pgoff_t offset;
  
  	spin_lock(&swap_lock);
  	si = swap_info + type;
  	if (si->flags & SWP_WRITEOK) {
  		nr_swap_pages--;
  		offset = scan_swap_map(si);
  		if (offset) {
  			spin_unlock(&swap_lock);
  			return swp_entry(type, offset);
  		}
  		nr_swap_pages++;
  	}
  	spin_unlock(&swap_lock);
  	return (swp_entry_t) {0};
  }

  static struct swap_info_struct * swap_info_get(swp_entry_t entry)
  {
  	struct swap_info_struct * p;
  	unsigned long offset, type;
  
  	if (!entry.val)
  		goto out;
  	type = swp_type(entry);
  	if (type >= nr_swapfiles)
  		goto bad_nofile;
  	p = & swap_info[type];
  	if (!(p->flags & SWP_USED))
  		goto bad_device;
  	offset = swp_offset(entry);
  	if (offset >= p->max)
  		goto bad_offset;
  	if (!p->swap_map[offset])
  		goto bad_free;

  	spin_lock(&swap_lock);

  	return p;
  
  bad_free:
  	printk(KERN_ERR "swap_free: %s%08lx
  ", Unused_offset, entry.val);
  	goto out;
  bad_offset:
  	printk(KERN_ERR "swap_free: %s%08lx
  ", Bad_offset, entry.val);
  	goto out;
  bad_device:
  	printk(KERN_ERR "swap_free: %s%08lx
  ", Unused_file, entry.val);
  	goto out;
  bad_nofile:
  	printk(KERN_ERR "swap_free: %s%08lx
  ", Bad_file, entry.val);
  out:
  	return NULL;
  }	

  static int swap_entry_free(struct swap_info_struct *p, unsigned long offset)
  {
  	int count = p->swap_map[offset];
  
  	if (count < SWAP_MAP_MAX) {
  		count--;
  		p->swap_map[offset] = count;
  		if (!count) {
  			if (offset < p->lowest_bit)
  				p->lowest_bit = offset;
  			if (offset > p->highest_bit)
  				p->highest_bit = offset;

  			if (p->prio > swap_info[swap_list.next].prio)
  				swap_list.next = p - swap_info;

  			nr_swap_pages++;
  			p->inuse_pages--;
  		}
  	}
  	return count;
  }
  
  /*
   * Caller has made sure that the swapdevice corresponding to entry
   * is still around or has not been recycled.
   */
  void swap_free(swp_entry_t entry)
  {
  	struct swap_info_struct * p;
  
  	p = swap_info_get(entry);
  	if (p) {
  		swap_entry_free(p, swp_offset(entry));

  		spin_unlock(&swap_lock);

  	}
  }
  
  /*

   * How many references to page are currently swapped out?

   */

  static inline int page_swapcount(struct page *page)

  {

  	int count = 0;
  	struct swap_info_struct *p;

  	swp_entry_t entry;

  	entry.val = page_private(page);

  	p = swap_info_get(entry);
  	if (p) {

  		/* Subtract the 1 for the swap cache itself */
  		count = p->swap_map[swp_offset(entry)] - 1;

  		spin_unlock(&swap_lock);

  	}

  	return count;

  }
  
  /*
   * We can use this swap cache entry directly
   * if there are no other references to it.

   */
  int can_share_swap_page(struct page *page)
  {

  	int count;
  
  	BUG_ON(!PageLocked(page));
  	count = page_mapcount(page);
  	if (count <= 1 && PageSwapCache(page))
  		count += page_swapcount(page);
  	return count == 1;

  }
  
  /*
   * Work out if there are any other processes sharing this
   * swap cache page. Free it if you can. Return success.
   */
  int remove_exclusive_swap_page(struct page *page)
  {
  	int retval;
  	struct swap_info_struct * p;
  	swp_entry_t entry;
  
  	BUG_ON(PagePrivate(page));
  	BUG_ON(!PageLocked(page));
  
  	if (!PageSwapCache(page))
  		return 0;
  	if (PageWriteback(page))
  		return 0;
  	if (page_count(page) != 2) /* 2: us + cache */
  		return 0;

  	entry.val = page_private(page);

  	p = swap_info_get(entry);
  	if (!p)
  		return 0;
  
  	/* Is the only swap cache user the cache itself? */
  	retval = 0;
  	if (p->swap_map[swp_offset(entry)] == 1) {
  		/* Recheck the page count with the swapcache lock held.. */

  		spin_lock_irq(&swapper_space.tree_lock);

  		if ((page_count(page) == 2) && !PageWriteback(page)) {
  			__delete_from_swap_cache(page);
  			SetPageDirty(page);
  			retval = 1;
  		}

  		spin_unlock_irq(&swapper_space.tree_lock);

  	}

  	spin_unlock(&swap_lock);

  
  	if (retval) {
  		swap_free(entry);
  		page_cache_release(page);
  	}
  
  	return retval;
  }
  
  /*
   * Free the swap entry like above, but also try to
   * free the page cache entry if it is the last user.
   */
  void free_swap_and_cache(swp_entry_t entry)
  {
  	struct swap_info_struct * p;
  	struct page *page = NULL;

  	if (is_migration_entry(entry))
  		return;

  	p = swap_info_get(entry);
  	if (p) {

  		if (swap_entry_free(p, swp_offset(entry)) == 1) {
  			page = find_get_page(&swapper_space, entry.val);

  			if (page && unlikely(!trylock_page(page))) {

  				page_cache_release(page);
  				page = NULL;
  			}
  		}

  		spin_unlock(&swap_lock);

  	}
  	if (page) {
  		int one_user;
  
  		BUG_ON(PagePrivate(page));

  		one_user = (page_count(page) == 2);
  		/* Only cache user (+us), or swap space full? Free it! */

  		/* Also recheck PageSwapCache after page is locked (above) */
  		if (PageSwapCache(page) && !PageWriteback(page) &&
  					(one_user || vm_swap_full())) {

  			delete_from_swap_cache(page);
  			SetPageDirty(page);
  		}
  		unlock_page(page);
  		page_cache_release(page);
  	}
  }

  #ifdef CONFIG_HIBERNATION

  /*

   * Find the swap type that corresponds to given device (if any).

   *

   * @offset - number of the PAGE_SIZE-sized block of the device, starting
   * from 0, in which the swap header is expected to be located.
   *
   * This is needed for the suspend to disk (aka swsusp).

   */

  int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)

  {

  	struct block_device *bdev = NULL;

  	int i;

  	if (device)
  		bdev = bdget(device);

  	spin_lock(&swap_lock);
  	for (i = 0; i < nr_swapfiles; i++) {

  		struct swap_info_struct *sis = swap_info + i;

  		if (!(sis->flags & SWP_WRITEOK))

  			continue;

  		if (!bdev) {

  			if (bdev_p)
  				*bdev_p = sis->bdev;

  			spin_unlock(&swap_lock);
  			return i;
  		}

  		if (bdev == sis->bdev) {
  			struct swap_extent *se;
  
  			se = list_entry(sis->extent_list.next,
  					struct swap_extent, list);
  			if (se->start_block == offset) {

  				if (bdev_p)
  					*bdev_p = sis->bdev;

  				spin_unlock(&swap_lock);
  				bdput(bdev);
  				return i;
  			}

  		}
  	}
  	spin_unlock(&swap_lock);

  	if (bdev)
  		bdput(bdev);

  	return -ENODEV;
  }
  
  /*
   * Return either the total number of swap pages of given type, or the number
   * of free pages of that type (depending on @free)
   *
   * This is needed for software suspend
   */
  unsigned int count_swap_pages(int type, int free)
  {
  	unsigned int n = 0;
  
  	if (type < nr_swapfiles) {
  		spin_lock(&swap_lock);
  		if (swap_info[type].flags & SWP_WRITEOK) {
  			n = swap_info[type].pages;
  			if (free)
  				n -= swap_info[type].inuse_pages;
  		}
  		spin_unlock(&swap_lock);
  	}
  	return n;
  }
  #endif

  /*

   * No need to decide whether this PTE shares the swap entry with others,
   * just let do_wp_page work it out if a write is requested later - to
   * force COW, vm_page_prot omits write permission from any private vma.

   */

  static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,

  		unsigned long addr, swp_entry_t entry, struct page *page)
  {

  	spinlock_t *ptl;
  	pte_t *pte;
  	int ret = 1;

  	if (mem_cgroup_charge(page, vma->vm_mm, GFP_KERNEL))

  		ret = -ENOMEM;
  
  	pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
  	if (unlikely(!pte_same(*pte, swp_entry_to_pte(entry)))) {
  		if (ret > 0)
  			mem_cgroup_uncharge_page(page);
  		ret = 0;
  		goto out;
  	}

  	inc_mm_counter(vma->vm_mm, anon_rss);

  	get_page(page);
  	set_pte_at(vma->vm_mm, addr, pte,
  		   pte_mkold(mk_pte(page, vma->vm_page_prot)));
  	page_add_anon_rmap(page, vma, addr);
  	swap_free(entry);
  	/*
  	 * Move the page to the active list so it is not
  	 * immediately swapped out again after swapon.
  	 */
  	activate_page(page);

  out:
  	pte_unmap_unlock(pte, ptl);
  	return ret;

  }
  
  static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
  				unsigned long addr, unsigned long end,
  				swp_entry_t entry, struct page *page)
  {

  	pte_t swp_pte = swp_entry_to_pte(entry);

  	pte_t *pte;

  	int ret = 0;

  	/*
  	 * We don't actually need pte lock while scanning for swp_pte: since
  	 * we hold page lock and mmap_sem, swp_pte cannot be inserted into the
  	 * page table while we're scanning; though it could get zapped, and on
  	 * some architectures (e.g. x86_32 with PAE) we might catch a glimpse
  	 * of unmatched parts which look like swp_pte, so unuse_pte must
  	 * recheck under pte lock.  Scanning without pte lock lets it be
  	 * preemptible whenever CONFIG_PREEMPT but not CONFIG_HIGHPTE.
  	 */
  	pte = pte_offset_map(pmd, addr);

  	do {
  		/*
  		 * swapoff spends a _lot_ of time in this loop!
  		 * Test inline before going to call unuse_pte.
  		 */
  		if (unlikely(pte_same(*pte, swp_pte))) {

  			pte_unmap(pte);
  			ret = unuse_pte(vma, pmd, addr, entry, page);
  			if (ret)
  				goto out;
  			pte = pte_offset_map(pmd, addr);

  		}
  	} while (pte++, addr += PAGE_SIZE, addr != end);

  	pte_unmap(pte - 1);
  out:

  	return ret;

  }
  
  static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
  				unsigned long addr, unsigned long end,
  				swp_entry_t entry, struct page *page)
  {
  	pmd_t *pmd;
  	unsigned long next;

  	int ret;

  
  	pmd = pmd_offset(pud, addr);
  	do {
  		next = pmd_addr_end(addr, end);
  		if (pmd_none_or_clear_bad(pmd))
  			continue;

  		ret = unuse_pte_range(vma, pmd, addr, next, entry, page);
  		if (ret)
  			return ret;

  	} while (pmd++, addr = next, addr != end);
  	return 0;
  }
  
  static inline int unuse_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
  				unsigned long addr, unsigned long end,
  				swp_entry_t entry, struct page *page)
  {
  	pud_t *pud;
  	unsigned long next;

  	int ret;

  
  	pud = pud_offset(pgd, addr);
  	do {
  		next = pud_addr_end(addr, end);
  		if (pud_none_or_clear_bad(pud))
  			continue;

  		ret = unuse_pmd_range(vma, pud, addr, next, entry, page);
  		if (ret)
  			return ret;

  	} while (pud++, addr = next, addr != end);
  	return 0;
  }
  
  static int unuse_vma(struct vm_area_struct *vma,
  				swp_entry_t entry, struct page *page)
  {
  	pgd_t *pgd;
  	unsigned long addr, end, next;

  	int ret;

  
  	if (page->mapping) {
  		addr = page_address_in_vma(page, vma);
  		if (addr == -EFAULT)
  			return 0;
  		else
  			end = addr + PAGE_SIZE;
  	} else {
  		addr = vma->vm_start;
  		end = vma->vm_end;
  	}
  
  	pgd = pgd_offset(vma->vm_mm, addr);
  	do {
  		next = pgd_addr_end(addr, end);
  		if (pgd_none_or_clear_bad(pgd))
  			continue;

  		ret = unuse_pud_range(vma, pgd, addr, next, entry, page);
  		if (ret)
  			return ret;

  	} while (pgd++, addr = next, addr != end);
  	return 0;
  }
  
  static int unuse_mm(struct mm_struct *mm,
  				swp_entry_t entry, struct page *page)
  {
  	struct vm_area_struct *vma;

  	int ret = 0;

  
  	if (!down_read_trylock(&mm->mmap_sem)) {
  		/*

  		 * Activate page so shrink_inactive_list is unlikely to unmap
  		 * its ptes while lock is dropped, so swapoff can make progress.

  		 */

  		activate_page(page);

  		unlock_page(page);
  		down_read(&mm->mmap_sem);
  		lock_page(page);
  	}

  	for (vma = mm->mmap; vma; vma = vma->vm_next) {

  		if (vma->anon_vma && (ret = unuse_vma(vma, entry, page)))

  			break;
  	}

  	up_read(&mm->mmap_sem);

  	return (ret < 0)? ret: 0;

  }
  
  /*
   * Scan swap_map from current position to next entry still in use.
   * Recycle to start on reaching the end, returning 0 when empty.
   */

  static unsigned int find_next_to_unuse(struct swap_info_struct *si,
  					unsigned int prev)

  {

  	unsigned int max = si->max;
  	unsigned int i = prev;

  	int count;
  
  	/*

  	 * No need for swap_lock here: we're just looking

  	 * for whether an entry is in use, not modifying it; false
  	 * hits are okay, and sys_swapoff() has already prevented new

  	 * allocations from this area (while holding swap_lock).

  	 */
  	for (;;) {
  		if (++i >= max) {
  			if (!prev) {
  				i = 0;
  				break;
  			}
  			/*
  			 * No entries in use at top of swap_map,
  			 * loop back to start and recheck there.
  			 */
  			max = prev + 1;
  			prev = 0;
  			i = 1;
  		}
  		count = si->swap_map[i];
  		if (count && count != SWAP_MAP_BAD)
  			break;
  	}
  	return i;
  }
  
  /*
   * We completely avoid races by reading each swap page in advance,
   * and then search for the process using it.  All the necessary
   * page table adjustments can then be made atomically.
   */
  static int try_to_unuse(unsigned int type)
  {
  	struct swap_info_struct * si = &swap_info[type];
  	struct mm_struct *start_mm;
  	unsigned short *swap_map;
  	unsigned short swcount;
  	struct page *page;
  	swp_entry_t entry;

  	unsigned int i = 0;

  	int retval = 0;
  	int reset_overflow = 0;
  	int shmem;
  
  	/*
  	 * When searching mms for an entry, a good strategy is to
  	 * start at the first mm we freed the previous entry from
  	 * (though actually we don't notice whether we or coincidence
  	 * freed the entry).  Initialize this start_mm with a hold.
  	 *
  	 * A simpler strategy would be to start at the last mm we
  	 * freed the previous entry from; but that would take less
  	 * advantage of mmlist ordering, which clusters forked mms
  	 * together, child after parent.  If we race with dup_mmap(), we
  	 * prefer to resolve parent before child, lest we miss entries
  	 * duplicated after we scanned child: using last mm would invert
  	 * that.  Though it's only a serious concern when an overflowed
  	 * swap count is reset from SWAP_MAP_MAX, preventing a rescan.
  	 */
  	start_mm = &init_mm;
  	atomic_inc(&init_mm.mm_users);
  
  	/*
  	 * Keep on scanning until all entries have gone.  Usually,
  	 * one pass through swap_map is enough, but not necessarily:
  	 * there are races when an instance of an entry might be missed.
  	 */
  	while ((i = find_next_to_unuse(si, i)) != 0) {
  		if (signal_pending(current)) {
  			retval = -EINTR;
  			break;
  		}
  
  		/* 
  		 * Get a page for the entry, using the existing swap
  		 * cache page if there is one.  Otherwise, get a clean
  		 * page and read the swap into it. 
  		 */
  		swap_map = &si->swap_map[i];
  		entry = swp_entry(type, i);

  		page = read_swap_cache_async(entry,
  					GFP_HIGHUSER_MOVABLE, NULL, 0);

  		if (!page) {
  			/*
  			 * Either swap_duplicate() failed because entry
  			 * has been freed independently, and will not be
  			 * reused since sys_swapoff() already disabled
  			 * allocation from here, or alloc_page() failed.
  			 */
  			if (!*swap_map)
  				continue;
  			retval = -ENOMEM;
  			break;
  		}
  
  		/*
  		 * Don't hold on to start_mm if it looks like exiting.
  		 */
  		if (atomic_read(&start_mm->mm_users) == 1) {
  			mmput(start_mm);
  			start_mm = &init_mm;
  			atomic_inc(&init_mm.mm_users);
  		}
  
  		/*
  		 * Wait for and lock page.  When do_swap_page races with
  		 * try_to_unuse, do_swap_page can handle the fault much
  		 * faster than try_to_unuse can locate the entry.  This
  		 * apparently redundant "wait_on_page_locked" lets try_to_unuse
  		 * defer to do_swap_page in such a case - in some tests,
  		 * do_swap_page and try_to_unuse repeatedly compete.
  		 */
  		wait_on_page_locked(page);
  		wait_on_page_writeback(page);
  		lock_page(page);
  		wait_on_page_writeback(page);
  
  		/*
  		 * Remove all references to entry.
  		 * Whenever we reach init_mm, there's no address space
  		 * to search, but use it as a reminder to search shmem.
  		 */
  		shmem = 0;
  		swcount = *swap_map;
  		if (swcount > 1) {
  			if (start_mm == &init_mm)
  				shmem = shmem_unuse(entry, page);
  			else
  				retval = unuse_mm(start_mm, entry, page);
  		}
  		if (*swap_map > 1) {
  			int set_start_mm = (*swap_map >= swcount);
  			struct list_head *p = &start_mm->mmlist;
  			struct mm_struct *new_start_mm = start_mm;
  			struct mm_struct *prev_mm = start_mm;
  			struct mm_struct *mm;
  
  			atomic_inc(&new_start_mm->mm_users);
  			atomic_inc(&prev_mm->mm_users);
  			spin_lock(&mmlist_lock);

  			while (*swap_map > 1 && !retval && !shmem &&

  					(p = p->next) != &start_mm->mmlist) {
  				mm = list_entry(p, struct mm_struct, mmlist);

  				if (!atomic_inc_not_zero(&mm->mm_users))

  					continue;

  				spin_unlock(&mmlist_lock);
  				mmput(prev_mm);
  				prev_mm = mm;
  
  				cond_resched();
  
  				swcount = *swap_map;
  				if (swcount <= 1)
  					;
  				else if (mm == &init_mm) {
  					set_start_mm = 1;
  					shmem = shmem_unuse(entry, page);
  				} else
  					retval = unuse_mm(mm, entry, page);
  				if (set_start_mm && *swap_map < swcount) {
  					mmput(new_start_mm);
  					atomic_inc(&mm->mm_users);
  					new_start_mm = mm;
  					set_start_mm = 0;
  				}
  				spin_lock(&mmlist_lock);
  			}
  			spin_unlock(&mmlist_lock);
  			mmput(prev_mm);
  			mmput(start_mm);
  			start_mm = new_start_mm;
  		}

  		if (shmem) {
  			/* page has already been unlocked and released */
  			if (shmem > 0)
  				continue;
  			retval = shmem;
  			break;
  		}

  		if (retval) {
  			unlock_page(page);
  			page_cache_release(page);
  			break;
  		}
  
  		/*
  		 * How could swap count reach 0x7fff when the maximum
  		 * pid is 0x7fff, and there's no way to repeat a swap
  		 * page within an mm (except in shmem, where it's the
  		 * shared object which takes the reference count)?
  		 * We believe SWAP_MAP_MAX cannot occur in Linux 2.4.
  		 *
  		 * If that's wrong, then we should worry more about
  		 * exit_mmap() and do_munmap() cases described above:
  		 * we might be resetting SWAP_MAP_MAX too early here.
  		 * We know "Undead"s can happen, they're okay, so don't
  		 * report them; but do report if we reset SWAP_MAP_MAX.
  		 */
  		if (*swap_map == SWAP_MAP_MAX) {

  			spin_lock(&swap_lock);

  			*swap_map = 1;

  			spin_unlock(&swap_lock);

  			reset_overflow = 1;
  		}
  
  		/*
  		 * If a reference remains (rare), we would like to leave
  		 * the page in the swap cache; but try_to_unmap could
  		 * then re-duplicate the entry once we drop page lock,
  		 * so we might loop indefinitely; also, that page could
  		 * not be swapped out to other storage meanwhile.  So:
  		 * delete from cache even if there's another reference,
  		 * after ensuring that the data has been saved to disk -
  		 * since if the reference remains (rarer), it will be
  		 * read from disk into another page.  Splitting into two
  		 * pages would be incorrect if swap supported "shared
  		 * private" pages, but they are handled by tmpfs files.

  		 */
  		if ((*swap_map > 1) && PageDirty(page) && PageSwapCache(page)) {
  			struct writeback_control wbc = {
  				.sync_mode = WB_SYNC_NONE,
  			};
  
  			swap_writepage(page, &wbc);
  			lock_page(page);
  			wait_on_page_writeback(page);
  		}

  		if (PageSwapCache(page))
  			delete_from_swap_cache(page);

  
  		/*
  		 * So we could skip searching mms once swap count went
  		 * to 1, we did not mark any present ptes as dirty: must

  		 * mark page dirty so shrink_page_list will preserve it.

  		 */
  		SetPageDirty(page);
  		unlock_page(page);
  		page_cache_release(page);
  
  		/*
  		 * Make sure that we aren't completely killing
  		 * interactive performance.
  		 */
  		cond_resched();
  	}
  
  	mmput(start_mm);
  	if (reset_overflow) {
  		printk(KERN_WARNING "swapoff: cleared swap entry overflow
  ");
  		swap_overflow = 0;
  	}
  	return retval;
  }
  
  /*

   * After a successful try_to_unuse, if no swap is now in use, we know
   * we can empty the mmlist.  swap_lock must be held on entry and exit.
   * Note that mmlist_lock nests inside swap_lock, and an mm must be

   * added to the mmlist just after page_duplicate - before would be racy.
   */
  static void drain_mmlist(void)
  {
  	struct list_head *p, *next;
  	unsigned int i;
  
  	for (i = 0; i < nr_swapfiles; i++)
  		if (swap_info[i].inuse_pages)
  			return;
  	spin_lock(&mmlist_lock);
  	list_for_each_safe(p, next, &init_mm.mmlist)
  		list_del_init(p);
  	spin_unlock(&mmlist_lock);
  }
  
  /*
   * Use this swapdev's extent info to locate the (PAGE_SIZE) block which
   * corresponds to page offset `offset'.
   */
  sector_t map_swap_page(struct swap_info_struct *sis, pgoff_t offset)
  {
  	struct swap_extent *se = sis->curr_swap_extent;
  	struct swap_extent *start_se = se;
  
  	for ( ; ; ) {
  		struct list_head *lh;
  
  		if (se->start_page <= offset &&
  				offset < (se->start_page + se->nr_pages)) {
  			return se->start_block + (offset - se->start_page);
  		}

  		lh = se->list.next;

  		if (lh == &sis->extent_list)

  			lh = lh->next;

  		se = list_entry(lh, struct swap_extent, list);
  		sis->curr_swap_extent = se;
  		BUG_ON(se == start_se);		/* It *must* be present */
  	}
  }

  #ifdef CONFIG_HIBERNATION

  /*
   * Get the (PAGE_SIZE) block corresponding to given offset on the swapdev
   * corresponding to given index in swap_info (swap type).
   */
  sector_t swapdev_block(int swap_type, pgoff_t offset)
  {
  	struct swap_info_struct *sis;
  
  	if (swap_type >= nr_swapfiles)
  		return 0;
  
  	sis = swap_info + swap_type;
  	return (sis->flags & SWP_WRITEOK) ? map_swap_page(sis, offset) : 0;
  }

  #endif /* CONFIG_HIBERNATION */

  /*
   * Free all of a swapdev's extent information
   */
  static void destroy_swap_extents(struct swap_info_struct *sis)
  {
  	while (!list_empty(&sis->extent_list)) {
  		struct swap_extent *se;
  
  		se = list_entry(sis->extent_list.next,
  				struct swap_extent, list);
  		list_del(&se->list);
  		kfree(se);
  	}

  }
  
  /*
   * Add a block range (and the corresponding page range) into this swapdev's

   * extent list.  The extent list is kept sorted in page order.

   *

   * This function rather assumes that it is called in ascending page order.

   */
  static int
  add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
  		unsigned long nr_pages, sector_t start_block)
  {
  	struct swap_extent *se;
  	struct swap_extent *new_se;
  	struct list_head *lh;

  	lh = sis->extent_list.prev;	/* The highest page extent */
  	if (lh != &sis->extent_list) {

  		se = list_entry(lh, struct swap_extent, list);

  		BUG_ON(se->start_page + se->nr_pages != start_page);
  		if (se->start_block + se->nr_pages == start_block) {

  			/* Merge it */
  			se->nr_pages += nr_pages;
  			return 0;
  		}

  	}
  
  	/*
  	 * No merge.  Insert a new extent, preserving ordering.
  	 */
  	new_se = kmalloc(sizeof(*se), GFP_KERNEL);
  	if (new_se == NULL)
  		return -ENOMEM;
  	new_se->start_page = start_page;
  	new_se->nr_pages = nr_pages;
  	new_se->start_block = start_block;

  	list_add_tail(&new_se->list, &sis->extent_list);

  	return 1;

  }
  
  /*
   * A `swap extent' is a simple thing which maps a contiguous range of pages
   * onto a contiguous range of disk blocks.  An ordered list of swap extents
   * is built at swapon time and is then used at swap_writepage/swap_readpage
   * time for locating where on disk a page belongs.
   *
   * If the swapfile is an S_ISBLK block device, a single extent is installed.
   * This is done so that the main operating code can treat S_ISBLK and S_ISREG
   * swap files identically.
   *
   * Whether the swapdev is an S_ISREG file or an S_ISBLK blockdev, the swap
   * extent list operates in PAGE_SIZE disk blocks.  Both S_ISREG and S_ISBLK
   * swapfiles are handled *identically* after swapon time.
   *
   * For S_ISREG swapfiles, setup_swap_extents() will walk all the file's blocks
   * and will parse them into an ordered extent list, in PAGE_SIZE chunks.  If
   * some stray blocks are found which do not fall within the PAGE_SIZE alignment
   * requirements, they are simply tossed out - we will never use those blocks
   * for swapping.
   *

   * For S_ISREG swapfiles we set S_SWAPFILE across the life of the swapon.  This

   * prevents root from shooting her foot off by ftruncating an in-use swapfile,
   * which will scribble on the fs.
   *
   * The amount of disk space which a single swap extent represents varies.
   * Typically it is in the 1-4 megabyte range.  So we can have hundreds of
   * extents in the list.  To avoid much list walking, we cache the previous
   * search location in `curr_swap_extent', and start new searches from there.
   * This is extremely effective.  The average number of iterations in
   * map_swap_page() has been measured at about 0.3 per page.  - akpm.
   */

  static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)

  {
  	struct inode *inode;
  	unsigned blocks_per_page;
  	unsigned long page_no;
  	unsigned blkbits;
  	sector_t probe_block;
  	sector_t last_block;

  	sector_t lowest_block = -1;
  	sector_t highest_block = 0;
  	int nr_extents = 0;

  	int ret;
  
  	inode = sis->swap_file->f_mapping->host;
  	if (S_ISBLK(inode->i_mode)) {
  		ret = add_swap_extent(sis, 0, sis->max, 0);

  		*span = sis->pages;

  		goto done;
  	}
  
  	blkbits = inode->i_blkbits;
  	blocks_per_page = PAGE_SIZE >> blkbits;
  
  	/*
  	 * Map all the blocks into the extent list.  This code doesn't try
  	 * to be very smart.
  	 */
  	probe_block = 0;
  	page_no = 0;
  	last_block = i_size_read(inode) >> blkbits;
  	while ((probe_block + blocks_per_page) <= last_block &&
  			page_no < sis->max) {
  		unsigned block_in_page;
  		sector_t first_block;
  
  		first_block = bmap(inode, probe_block);
  		if (first_block == 0)
  			goto bad_bmap;
  
  		/*
  		 * It must be PAGE_SIZE aligned on-disk
  		 */
  		if (first_block & (blocks_per_page - 1)) {
  			probe_block++;
  			goto reprobe;
  		}
  
  		for (block_in_page = 1; block_in_page < blocks_per_page;
  					block_in_page++) {
  			sector_t block;
  
  			block = bmap(inode, probe_block + block_in_page);
  			if (block == 0)
  				goto bad_bmap;
  			if (block != first_block + block_in_page) {
  				/* Discontiguity */
  				probe_block++;
  				goto reprobe;
  			}
  		}

  		first_block >>= (PAGE_SHIFT - blkbits);
  		if (page_no) {	/* exclude the header page */
  			if (first_block < lowest_block)
  				lowest_block = first_block;
  			if (first_block > highest_block)
  				highest_block = first_block;
  		}

  		/*
  		 * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
  		 */

  		ret = add_swap_extent(sis, page_no, 1, first_block);
  		if (ret < 0)

  			goto out;

  		nr_extents += ret;

  		page_no++;
  		probe_block += blocks_per_page;
  reprobe:
  		continue;
  	}

  	ret = nr_extents;
  	*span = 1 + highest_block - lowest_block;

  	if (page_no == 0)

  		page_no = 1;	/* force Empty message */

  	sis->max = page_no;

  	sis->pages = page_no - 1;

  	sis->highest_bit = page_no - 1;
  done:
  	sis->curr_swap_extent = list_entry(sis->extent_list.prev,
  					struct swap_extent, list);
  	goto out;
  bad_bmap:
  	printk(KERN_ERR "swapon: swapfile has holes
  ");
  	ret = -EINVAL;
  out:
  	return ret;
  }
  
  #if 0	/* We don't need this yet */
  #include <linux/backing-dev.h>
  int page_queue_congested(struct page *page)
  {
  	struct backing_dev_info *bdi;
  
  	BUG_ON(!PageLocked(page));	/* It pins the swap_info_struct */
  
  	if (PageSwapCache(page)) {

  		swp_entry_t entry = { .val = page_private(page) };

  		struct swap_info_struct *sis;
  
  		sis = get_swap_info_struct(swp_type(entry));
  		bdi = sis->bdev->bd_inode->i_mapping->backing_dev_info;
  	} else
  		bdi = page->mapping->backing_dev_info;
  	return bdi_write_congested(bdi);
  }
  #endif
  
  asmlinkage long sys_swapoff(const char __user * specialfile)
  {
  	struct swap_info_struct * p = NULL;
  	unsigned short *swap_map;
  	struct file *swap_file, *victim;
  	struct address_space *mapping;
  	struct inode *inode;
  	char * pathname;
  	int i, type, prev;
  	int err;
  	
  	if (!capable(CAP_SYS_ADMIN))
  		return -EPERM;
  
  	pathname = getname(specialfile);
  	err = PTR_ERR(pathname);
  	if (IS_ERR(pathname))
  		goto out;
  
  	victim = filp_open(pathname, O_RDWR|O_LARGEFILE, 0);
  	putname(pathname);
  	err = PTR_ERR(victim);
  	if (IS_ERR(victim))
  		goto out;
  
  	mapping = victim->f_mapping;
  	prev = -1;

  	spin_lock(&swap_lock);

  	for (type = swap_list.head; type >= 0; type = swap_info[type].next) {
  		p = swap_info + type;
  		if ((p->flags & SWP_ACTIVE) == SWP_ACTIVE) {
  			if (p->swap_file->f_mapping == mapping)
  				break;
  		}
  		prev = type;
  	}
  	if (type < 0) {
  		err = -EINVAL;

  		spin_unlock(&swap_lock);

  		goto out_dput;
  	}
  	if (!security_vm_enough_memory(p->pages))
  		vm_unacct_memory(p->pages);
  	else {
  		err = -ENOMEM;

  		spin_unlock(&swap_lock);

  		goto out_dput;
  	}
  	if (prev < 0) {
  		swap_list.head = p->next;
  	} else {
  		swap_info[prev].next = p->next;
  	}
  	if (type == swap_list.next) {
  		/* just pick something that's safe... */
  		swap_list.next = swap_list.head;
  	}

  	if (p->prio < 0) {
  		for (i = p->next; i >= 0; i = swap_info[i].next)
  			swap_info[i].prio = p->prio--;
  		least_priority++;
  	}

  	nr_swap_pages -= p->pages;
  	total_swap_pages -= p->pages;
  	p->flags &= ~SWP_WRITEOK;

  	spin_unlock(&swap_lock);

  	current->flags |= PF_SWAPOFF;
  	err = try_to_unuse(type);
  	current->flags &= ~PF_SWAPOFF;

  	if (err) {
  		/* re-insert swap space back into swap_list */

  		spin_lock(&swap_lock);

  		if (p->prio < 0)
  			p->prio = --least_priority;
  		prev = -1;
  		for (i = swap_list.head; i >= 0; i = swap_info[i].next) {

  			if (p->prio >= swap_info[i].prio)
  				break;

  			prev = i;
  		}

  		p->next = i;
  		if (prev < 0)
  			swap_list.head = swap_list.next = p - swap_info;
  		else
  			swap_info[prev].next = p - swap_info;
  		nr_swap_pages += p->pages;
  		total_swap_pages += p->pages;
  		p->flags |= SWP_WRITEOK;

  		spin_unlock(&swap_lock);

  		goto out_dput;
  	}

  
  	/* wait for any unplug function to finish */
  	down_write(&swap_unplug_sem);
  	up_write(&swap_unplug_sem);

  	destroy_swap_extents(p);

  	mutex_lock(&swapon_mutex);

  	spin_lock(&swap_lock);
  	drain_mmlist();

  	/* wait for anyone still in scan_swap_map */

  	p->highest_bit = 0;		/* cuts scans short */
  	while (p->flags >= SWP_SCANNING) {

  		spin_unlock(&swap_lock);

  		schedule_timeout_uninterruptible(1);

  		spin_lock(&swap_lock);

  	}

  	swap_file = p->swap_file;
  	p->swap_file = NULL;
  	p->max = 0;
  	swap_map = p->swap_map;
  	p->swap_map = NULL;
  	p->flags = 0;

  	spin_unlock(&swap_lock);

  	mutex_unlock(&swapon_mutex);

  	vfree(swap_map);
  	inode = mapping->host;
  	if (S_ISBLK(inode->i_mode)) {
  		struct block_device *bdev = I_BDEV(inode);
  		set_blocksize(bdev, p->old_block_size);
  		bd_release(bdev);
  	} else {

  		mutex_lock(&inode->i_mutex);

  		inode->i_flags &= ~S_SWAPFILE;

  		mutex_unlock(&inode->i_mutex);

  	}
  	filp_close(swap_file, NULL);
  	err = 0;
  
  out_dput:
  	filp_close(victim, NULL);
  out:
  	return err;
  }
  
  #ifdef CONFIG_PROC_FS
  /* iterator */
  static void *swap_start(struct seq_file *swap, loff_t *pos)
  {
  	struct swap_info_struct *ptr = swap_info;
  	int i;
  	loff_t l = *pos;

  	mutex_lock(&swapon_mutex);

  	if (!l)
  		return SEQ_START_TOKEN;

  	for (i = 0; i < nr_swapfiles; i++, ptr++) {
  		if (!(ptr->flags & SWP_USED) || !ptr->swap_map)
  			continue;

  		if (!--l)

  			return ptr;
  	}
  
  	return NULL;
  }
  
  static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
  {

  	struct swap_info_struct *ptr;

  	struct swap_info_struct *endptr = swap_info + nr_swapfiles;

  	if (v == SEQ_START_TOKEN)
  		ptr = swap_info;
  	else {
  		ptr = v;
  		ptr++;
  	}
  
  	for (; ptr < endptr; ptr++) {

  		if (!(ptr->flags & SWP_USED) || !ptr->swap_map)
  			continue;
  		++*pos;
  		return ptr;
  	}
  
  	return NULL;
  }
  
  static void swap_stop(struct seq_file *swap, void *v)
  {

  	mutex_unlock(&swapon_mutex);

  }
  
  static int swap_show(struct seq_file *swap, void *v)
  {
  	struct swap_info_struct *ptr = v;
  	struct file *file;
  	int len;

  	if (ptr == SEQ_START_TOKEN) {
  		seq_puts(swap,"Filename\t\t\t\tType\t\tSize\tUsed\tPriority
  ");
  		return 0;
  	}

  
  	file = ptr->swap_file;

  	len = seq_path(swap, &file->f_path, " \t
  \\");

  	seq_printf(swap, "%*s%s\t%u\t%u\t%d
  ",

  		       len < 40 ? 40 - len : 1, " ",

  		       S_ISBLK(file->f_path.dentry->d_inode->i_mode) ?

  				"partition" : "file\t",
  		       ptr->pages << (PAGE_SHIFT - 10),
  		       ptr->inuse_pages << (PAGE_SHIFT - 10),
  		       ptr->prio);
  	return 0;
  }

  static const struct seq_operations swaps_op = {

  	.start =	swap_start,
  	.next =		swap_next,
  	.stop =		swap_stop,
  	.show =		swap_show
  };
  
  static int swaps_open(struct inode *inode, struct file *file)
  {
  	return seq_open(file, &swaps_op);
  }

  static const struct file_operations proc_swaps_operations = {

  	.open		= swaps_open,
  	.read		= seq_read,
  	.llseek		= seq_lseek,
  	.release	= seq_release,
  };
  
  static int __init procswaps_init(void)
  {

  	proc_create("swaps", 0, NULL, &proc_swaps_operations);

  	return 0;
  }
  __initcall(procswaps_init);
  #endif /* CONFIG_PROC_FS */
  
  /*
   * Written 01/25/92 by Simmule Turner, heavily changed by Linus.
   *
   * The swapon system call
   */
  asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags)
  {
  	struct swap_info_struct * p;
  	char *name = NULL;
  	struct block_device *bdev = NULL;
  	struct file *swap_file = NULL;
  	struct address_space *mapping;
  	unsigned int type;
  	int i, prev;
  	int error;

  	union swap_header *swap_header = NULL;
  	int swap_header_version;

  	unsigned int nr_good_pages = 0;
  	int nr_extents = 0;

  	sector_t span;

  	unsigned long maxpages = 1;
  	int swapfilesize;

  	unsigned short *swap_map = NULL;

  	struct page *page = NULL;
  	struct inode *inode = NULL;
  	int did_down = 0;
  
  	if (!capable(CAP_SYS_ADMIN))
  		return -EPERM;

  	spin_lock(&swap_lock);

  	p = swap_info;
  	for (type = 0 ; type < nr_swapfiles ; type++,p++)
  		if (!(p->flags & SWP_USED))
  			break;
  	error = -EPERM;

  	if (type >= MAX_SWAPFILES) {

  		spin_unlock(&swap_lock);

  		goto out;
  	}
  	if (type >= nr_swapfiles)
  		nr_swapfiles = type+1;

  	memset(p, 0, sizeof(*p));

  	INIT_LIST_HEAD(&p->extent_list);
  	p->flags = SWP_USED;

  	p->next = -1;

  	spin_unlock(&swap_lock);

  	name = getname(specialfile);
  	error = PTR_ERR(name);
  	if (IS_ERR(name)) {
  		name = NULL;
  		goto bad_swap_2;
  	}
  	swap_file = filp_open(name, O_RDWR|O_LARGEFILE, 0);
  	error = PTR_ERR(swap_file);
  	if (IS_ERR(swap_file)) {
  		swap_file = NULL;
  		goto bad_swap_2;
  	}
  
  	p->swap_file = swap_file;
  	mapping = swap_file->f_mapping;
  	inode = mapping->host;
  
  	error = -EBUSY;
  	for (i = 0; i < nr_swapfiles; i++) {
  		struct swap_info_struct *q = &swap_info[i];
  
  		if (i == type || !q->swap_file)
  			continue;
  		if (mapping == q->swap_file->f_mapping)
  			goto bad_swap;
  	}
  
  	error = -EINVAL;
  	if (S_ISBLK(inode->i_mode)) {
  		bdev = I_BDEV(inode);
  		error = bd_claim(bdev, sys_swapon);
  		if (error < 0) {
  			bdev = NULL;

  			error = -EINVAL;

  			goto bad_swap;
  		}
  		p->old_block_size = block_size(bdev);
  		error = set_blocksize(bdev, PAGE_SIZE);
  		if (error < 0)
  			goto bad_swap;
  		p->bdev = bdev;
  	} else if (S_ISREG(inode->i_mode)) {
  		p->bdev = inode->i_sb->s_bdev;

  		mutex_lock(&inode->i_mutex);

  		did_down = 1;
  		if (IS_SWAPFILE(inode)) {
  			error = -EBUSY;
  			goto bad_swap;
  		}
  	} else {
  		goto bad_swap;
  	}
  
  	swapfilesize = i_size_read(inode) >> PAGE_SHIFT;
  
  	/*
  	 * Read the swap header.
  	 */
  	if (!mapping->a_ops->readpage) {
  		error = -EINVAL;
  		goto bad_swap;
  	}

  	page = read_mapping_page(mapping, 0, swap_file);

  	if (IS_ERR(page)) {
  		error = PTR_ERR(page);
  		goto bad_swap;
  	}

  	kmap(page);
  	swap_header = page_address(page);
  
  	if (!memcmp("SWAP-SPACE",swap_header->magic.magic,10))
  		swap_header_version = 1;
  	else if (!memcmp("SWAPSPACE2",swap_header->magic.magic,10))
  		swap_header_version = 2;
  	else {

  		printk(KERN_ERR "Unable to find swap-space signature
  ");

  		error = -EINVAL;
  		goto bad_swap;
  	}
  	
  	switch (swap_header_version) {
  	case 1:
  		printk(KERN_ERR "version 0 swap is no longer supported. "
  			"Use mkswap -v1 %s
  ", name);
  		error = -EINVAL;
  		goto bad_swap;
  	case 2:

  		/* swap partition endianess hack... */
  		if (swab32(swap_header->info.version) == 1) {
  			swab32s(&swap_header->info.version);
  			swab32s(&swap_header->info.last_page);
  			swab32s(&swap_header->info.nr_badpages);
  			for (i = 0; i < swap_header->info.nr_badpages; i++)
  				swab32s(&swap_header->info.badpages[i]);
  		}

  		/* Check the swap header's sub-version and the size of
                     the swap file and bad block lists */
  		if (swap_header->info.version != 1) {
  			printk(KERN_WARNING
  			       "Unable to handle swap header version %d
  ",
  			       swap_header->info.version);
  			error = -EINVAL;
  			goto bad_swap;
  		}
  
  		p->lowest_bit  = 1;

  		p->cluster_next = 1;

  		/*
  		 * Find out how many pages are allowed for a single swap
  		 * device. There are two limiting factors: 1) the number of
  		 * bits for the swap offset in the swp_entry_t type and
  		 * 2) the number of bits in the a swap pte as defined by
  		 * the different architectures. In order to find the
  		 * largest possible bit mask a swap entry with swap type 0
  		 * and swap offset ~0UL is created, encoded to a swap pte,
  		 * decoded to a swp_entry_t again and finally the swap
  		 * offset is extracted. This will mask all the bits from
  		 * the initial ~0UL mask that can't be encoded in either
  		 * the swp_entry_t or the architecture definition of a
  		 * swap pte.
  		 */
  		maxpages = swp_offset(pte_to_swp_entry(swp_entry_to_pte(swp_entry(0,~0UL)))) - 1;
  		if (maxpages > swap_header->info.last_page)
  			maxpages = swap_header->info.last_page;
  		p->highest_bit = maxpages - 1;
  
  		error = -EINVAL;

  		if (!maxpages)
  			goto bad_swap;

  		if (swapfilesize && maxpages > swapfilesize) {
  			printk(KERN_WARNING
  			       "Swap area shorter than signature indicates
  ");
  			goto bad_swap;
  		}

  		if (swap_header->info.nr_badpages && S_ISREG(inode->i_mode))
  			goto bad_swap;

  		if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
  			goto bad_swap;

  		/* OK, set up the swap map and apply the bad block list */

  		swap_map = vmalloc(maxpages * sizeof(short));
  		if (!swap_map) {

  			error = -ENOMEM;
  			goto bad_swap;
  		}
  
  		error = 0;

  		memset(swap_map, 0, maxpages * sizeof(short));

  		for (i = 0; i < swap_header->info.nr_badpages; i++) {
  			int page_nr = swap_header->info.badpages[i];
  			if (page_nr <= 0 || page_nr >= swap_header->info.last_page)

  				error = -EINVAL;
  			else

  				swap_map[page_nr] = SWAP_MAP_BAD;

  		}
  		nr_good_pages = swap_header->info.last_page -
  				swap_header->info.nr_badpages -
  				1 /* header page */;

  		if (error)

  			goto bad_swap;
  	}

  	if (nr_good_pages) {

  		swap_map[0] = SWAP_MAP_BAD;

  		p->max = maxpages;
  		p->pages = nr_good_pages;

  		nr_extents = setup_swap_extents(p, &span);
  		if (nr_extents < 0) {
  			error = nr_extents;

  			goto bad_swap;

  		}

  		nr_good_pages = p->pages;
  	}

  	if (!nr_good_pages) {
  		printk(KERN_WARNING "Empty swap-file
  ");
  		error = -EINVAL;
  		goto bad_swap;
  	}

  	mutex_lock(&swapon_mutex);

  	spin_lock(&swap_lock);

  	if (swap_flags & SWAP_FLAG_PREFER)
  		p->prio =
  		  (swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SHIFT;
  	else
  		p->prio = --least_priority;
  	p->swap_map = swap_map;

  	p->flags = SWP_ACTIVE;
  	nr_swap_pages += nr_good_pages;
  	total_swap_pages += nr_good_pages;

  	printk(KERN_INFO "Adding %uk swap on %s.  "

  			"Priority:%d extents:%d across:%lluk
  ",
  		nr_good_pages<<(PAGE_SHIFT-10), name, p->prio,
  		nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10));

  
  	/* insert swap space into swap_list: */
  	prev = -1;
  	for (i = swap_list.head; i >= 0; i = swap_info[i].next) {
  		if (p->prio >= swap_info[i].prio) {
  			break;
  		}
  		prev = i;
  	}
  	p->next = i;
  	if (prev < 0) {
  		swap_list.head = swap_list.next = p - swap_info;
  	} else {
  		swap_info[prev].next = p - swap_info;
  	}

  	spin_unlock(&swap_lock);

  	mutex_unlock(&swapon_mutex);

  	error = 0;
  	goto out;
  bad_swap:
  	if (bdev) {
  		set_blocksize(bdev, p->old_block_size);
  		bd_release(bdev);
  	}

  	destroy_swap_extents(p);

  bad_swap_2:

  	spin_lock(&swap_lock);

  	p->swap_file = NULL;

  	p->flags = 0;

  	spin_unlock(&swap_lock);

  	vfree(swap_map);
  	if (swap_file)
  		filp_close(swap_file, NULL);
  out:
  	if (page && !IS_ERR(page)) {
  		kunmap(page);
  		page_cache_release(page);
  	}
  	if (name)
  		putname(name);
  	if (did_down) {
  		if (!error)
  			inode->i_flags |= S_SWAPFILE;

  		mutex_unlock(&inode->i_mutex);

  	}
  	return error;
  }
  
  void si_swapinfo(struct sysinfo *val)
  {
  	unsigned int i;
  	unsigned long nr_to_be_unused = 0;

  	spin_lock(&swap_lock);

  	for (i = 0; i < nr_swapfiles; i++) {
  		if (!(swap_info[i].flags & SWP_USED) ||
  		     (swap_info[i].flags & SWP_WRITEOK))
  			continue;
  		nr_to_be_unused += swap_info[i].inuse_pages;
  	}
  	val->freeswap = nr_swap_pages + nr_to_be_unused;
  	val->totalswap = total_swap_pages + nr_to_be_unused;

  	spin_unlock(&swap_lock);

  }
  
  /*
   * Verify that a swap entry is valid and increment its swap map count.
   *
   * Note: if swap_map[] reaches SWAP_MAP_MAX the entries are treated as
   * "permanent", but will be reclaimed by the next swapoff.
   */
  int swap_duplicate(swp_entry_t entry)
  {
  	struct swap_info_struct * p;
  	unsigned long offset, type;
  	int result = 0;

  	if (is_migration_entry(entry))
  		return 1;

  	type = swp_type(entry);
  	if (type >= nr_swapfiles)
  		goto bad_file;
  	p = type + swap_info;
  	offset = swp_offset(entry);

  	spin_lock(&swap_lock);

  	if (offset < p->max && p->swap_map[offset]) {
  		if (p->swap_map[offset] < SWAP_MAP_MAX - 1) {
  			p->swap_map[offset]++;
  			result = 1;
  		} else if (p->swap_map[offset] <= SWAP_MAP_MAX) {
  			if (swap_overflow++ < 5)
  				printk(KERN_WARNING "swap_dup: swap entry overflow
  ");
  			p->swap_map[offset] = SWAP_MAP_MAX;
  			result = 1;
  		}
  	}

  	spin_unlock(&swap_lock);

  out:
  	return result;
  
  bad_file:
  	printk(KERN_ERR "swap_dup: %s%08lx
  ", Bad_file, entry.val);
  	goto out;
  }
  
  struct swap_info_struct *
  get_swap_info_struct(unsigned type)
  {
  	return &swap_info[type];
  }
  
  /*

   * swap_lock prevents swap_map being freed. Don't grab an extra

   * reference on the swaphandle, it doesn't matter if it becomes unused.
   */
  int valid_swaphandles(swp_entry_t entry, unsigned long *offset)
  {

  	struct swap_info_struct *si;

  	int our_page_cluster = page_cluster;

  	pgoff_t target, toff;
  	pgoff_t base, end;
  	int nr_pages = 0;

  	if (!our_page_cluster)	/* no readahead */

  		return 0;

  
  	si = &swap_info[swp_type(entry)];
  	target = swp_offset(entry);
  	base = (target >> our_page_cluster) << our_page_cluster;
  	end = base + (1 << our_page_cluster);
  	if (!base)		/* first page is swap header */
  		base++;

  	spin_lock(&swap_lock);

  	if (end > si->max)	/* don't go beyond end of map */
  		end = si->max;
  
  	/* Count contiguous allocated slots above our target */
  	for (toff = target; ++toff < end; nr_pages++) {
  		/* Don't read in free or bad pages */
  		if (!si->swap_map[toff])
  			break;
  		if (si->swap_map[toff] == SWAP_MAP_BAD)

  			break;

  	}
  	/* Count contiguous allocated slots below our target */
  	for (toff = target; --toff >= base; nr_pages++) {

  		/* Don't read in free or bad pages */

  		if (!si->swap_map[toff])

  			break;

  		if (si->swap_map[toff] == SWAP_MAP_BAD)

  			break;

  	}

  	spin_unlock(&swap_lock);

  
  	/*
  	 * Indicate starting offset, and return number of pages to get:
  	 * if only 1, say 0, since there's then no readahead to be done.
  	 */
  	*offset = ++toff;
  	return nr_pages? ++nr_pages: 0;

  }