/*
   *  linux/mm/swap_state.c
   *
   *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
   *  Swap reorganised 29.12.95, Stephen Tweedie
   *
   *  Rewritten to use page cache, (C) 1998 Stephen Tweedie
   */
  #include <linux/module.h>
  #include <linux/mm.h>
  #include <linux/kernel_stat.h>
  #include <linux/swap.h>
  #include <linux/init.h>
  #include <linux/pagemap.h>
  #include <linux/buffer_head.h>
  #include <linux/backing-dev.h>

  #include <linux/pagevec.h>

  #include <linux/migrate.h>

  
  #include <asm/pgtable.h>
  
  /*
   * swapper_space is a fiction, retained to simplify the path through

   * vmscan's shrink_page_list, to make sync_page look nicer, and to allow

   * future use of radix_tree tags in the swap cache.
   */

  static const struct address_space_operations swap_aops = {

  	.writepage	= swap_writepage,
  	.sync_page	= block_sync_page,
  	.set_page_dirty	= __set_page_dirty_nobuffers,

  	.migratepage	= migrate_page,

  };
  
  static struct backing_dev_info swap_backing_dev_info = {
  	.capabilities	= BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
  	.unplug_io_fn	= swap_unplug_io_fn,
  };
  
  struct address_space swapper_space = {
  	.page_tree	= RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),

  	.tree_lock	= __RW_LOCK_UNLOCKED(swapper_space.tree_lock),

  	.a_ops		= &swap_aops,
  	.i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear),
  	.backing_dev_info = &swap_backing_dev_info,
  };

  
  #define INC_CACHE_INFO(x)	do { swap_cache_info.x++; } while (0)
  
  static struct {
  	unsigned long add_total;
  	unsigned long del_total;
  	unsigned long find_success;
  	unsigned long find_total;
  	unsigned long noent_race;
  	unsigned long exist_race;
  } swap_cache_info;
  
  void show_swap_cache_info(void)
  {
  	printk("Swap cache: add %lu, delete %lu, find %lu/%lu, race %lu+%lu
  ",
  		swap_cache_info.add_total, swap_cache_info.del_total,
  		swap_cache_info.find_success, swap_cache_info.find_total,
  		swap_cache_info.noent_race, swap_cache_info.exist_race);
  	printk("Free swap  = %lukB
  ", nr_swap_pages << (PAGE_SHIFT - 10));
  	printk("Total swap = %lukB
  ", total_swap_pages << (PAGE_SHIFT - 10));
  }
  
  /*
   * __add_to_swap_cache resembles add_to_page_cache on swapper_space,
   * but sets SwapCache flag and private instead of mapping and index.
   */

  static int __add_to_swap_cache(struct page *page, swp_entry_t entry,

  			       gfp_t gfp_mask)

  {
  	int error;

  	BUG_ON(!PageLocked(page));

  	BUG_ON(PageSwapCache(page));
  	BUG_ON(PagePrivate(page));
  	error = radix_tree_preload(gfp_mask);
  	if (!error) {
  		write_lock_irq(&swapper_space.tree_lock);
  		error = radix_tree_insert(&swapper_space.page_tree,
  						entry.val, page);
  		if (!error) {
  			page_cache_get(page);

  			SetPageSwapCache(page);

  			set_page_private(page, entry.val);

  			total_swapcache_pages++;

  			__inc_zone_page_state(page, NR_FILE_PAGES);

  		}
  		write_unlock_irq(&swapper_space.tree_lock);
  		radix_tree_preload_end();
  	}
  	return error;
  }
  
  static int add_to_swap_cache(struct page *page, swp_entry_t entry)
  {
  	int error;

  	BUG_ON(PageLocked(page));

  	if (!swap_duplicate(entry)) {
  		INC_CACHE_INFO(noent_race);
  		return -ENOENT;
  	}

  	SetPageLocked(page);

  	error = __add_to_swap_cache(page, entry, GFP_KERNEL);
  	/*
  	 * Anon pages are already on the LRU, we don't run lru_cache_add here.
  	 */
  	if (error) {

  		ClearPageLocked(page);

  		swap_free(entry);
  		if (error == -EEXIST)
  			INC_CACHE_INFO(exist_race);
  		return error;
  	}
  	INC_CACHE_INFO(add_total);
  	return 0;
  }
  
  /*
   * This must be called only on pages that have
   * been verified to be in the swap cache.
   */
  void __delete_from_swap_cache(struct page *page)
  {
  	BUG_ON(!PageLocked(page));
  	BUG_ON(!PageSwapCache(page));
  	BUG_ON(PageWriteback(page));

  	BUG_ON(PagePrivate(page));

  	radix_tree_delete(&swapper_space.page_tree, page_private(page));
  	set_page_private(page, 0);

  	ClearPageSwapCache(page);
  	total_swapcache_pages--;

  	__dec_zone_page_state(page, NR_FILE_PAGES);

  	INC_CACHE_INFO(del_total);
  }
  
  /**
   * add_to_swap - allocate swap space for a page
   * @page: page we want to move to swap
   *
   * Allocate swap space for the page and add the page to the
   * swap cache.  Caller needs to hold the page lock. 
   */

  int add_to_swap(struct page * page, gfp_t gfp_mask)

  {
  	swp_entry_t entry;

  	int err;

  	BUG_ON(!PageLocked(page));

  
  	for (;;) {
  		entry = get_swap_page();
  		if (!entry.val)
  			return 0;

  		/*
  		 * Radix-tree node allocations from PF_MEMALLOC contexts could
  		 * completely exhaust the page allocator. __GFP_NOMEMALLOC
  		 * stops emergency reserves from being allocated.

  		 *

  		 * TODO: this could cause a theoretical memory reclaim
  		 * deadlock in the swap out path.

  		 */

  		/*
  		 * Add it to the swap cache and mark it dirty
  		 */

  		err = __add_to_swap_cache(page, entry,

  				gfp_mask|__GFP_NOMEMALLOC|__GFP_NOWARN);

  
  		switch (err) {
  		case 0:				/* Success */
  			SetPageUptodate(page);
  			SetPageDirty(page);
  			INC_CACHE_INFO(add_total);
  			return 1;
  		case -EEXIST:
  			/* Raced with "speculative" read_swap_cache_async */
  			INC_CACHE_INFO(exist_race);
  			swap_free(entry);
  			continue;
  		default:
  			/* -ENOMEM radix-tree allocation failure */
  			swap_free(entry);
  			return 0;
  		}
  	}
  }
  
  /*
   * This must be called only on pages that have
   * been verified to be in the swap cache and locked.
   * It will never put the page into the free list,
   * the caller has a reference on the page.
   */
  void delete_from_swap_cache(struct page *page)
  {
  	swp_entry_t entry;

  	entry.val = page_private(page);

  
  	write_lock_irq(&swapper_space.tree_lock);
  	__delete_from_swap_cache(page);
  	write_unlock_irq(&swapper_space.tree_lock);
  
  	swap_free(entry);
  	page_cache_release(page);
  }
  
  /*
   * Strange swizzling function only for use by shmem_writepage
   */
  int move_to_swap_cache(struct page *page, swp_entry_t entry)
  {
  	int err = __add_to_swap_cache(page, entry, GFP_ATOMIC);
  	if (!err) {
  		remove_from_page_cache(page);
  		page_cache_release(page);	/* pagecache ref */
  		if (!swap_duplicate(entry))
  			BUG();
  		SetPageDirty(page);
  		INC_CACHE_INFO(add_total);
  	} else if (err == -EEXIST)
  		INC_CACHE_INFO(exist_race);
  	return err;
  }
  
  /*
   * Strange swizzling function for shmem_getpage (and shmem_unuse)
   */
  int move_from_swap_cache(struct page *page, unsigned long index,
  		struct address_space *mapping)
  {
  	int err = add_to_page_cache(page, mapping, index, GFP_ATOMIC);
  	if (!err) {
  		delete_from_swap_cache(page);
  		/* shift page from clean_pages to dirty_pages list */
  		ClearPageDirty(page);
  		set_page_dirty(page);
  	}
  	return err;
  }
  
  /* 
   * If we are the only user, then try to free up the swap cache. 
   * 
   * Its ok to check for PageSwapCache without the page lock
   * here because we are going to recheck again inside 
   * exclusive_swap_page() _with_ the lock. 
   * 					- Marcelo
   */
  static inline void free_swap_cache(struct page *page)
  {
  	if (PageSwapCache(page) && !TestSetPageLocked(page)) {
  		remove_exclusive_swap_page(page);
  		unlock_page(page);
  	}
  }
  
  /* 
   * Perform a free_page(), also freeing any swap cache associated with

   * this page if it is the last user of the page.

   */
  void free_page_and_swap_cache(struct page *page)
  {
  	free_swap_cache(page);
  	page_cache_release(page);
  }
  
  /*
   * Passed an array of pages, drop them all from swapcache and then release
   * them.  They are removed from the LRU and freed if this is their last use.
   */
  void free_pages_and_swap_cache(struct page **pages, int nr)
  {

  	struct page **pagep = pages;
  
  	lru_add_drain();
  	while (nr) {

  		int todo = min(nr, PAGEVEC_SIZE);

  		int i;
  
  		for (i = 0; i < todo; i++)
  			free_swap_cache(pagep[i]);
  		release_pages(pagep, todo, 0);
  		pagep += todo;
  		nr -= todo;
  	}
  }
  
  /*
   * Lookup a swap entry in the swap cache. A found page will be returned
   * unlocked and with its refcount incremented - we rely on the kernel
   * lock getting page table operations atomic even if we drop the page
   * lock before returning.
   */
  struct page * lookup_swap_cache(swp_entry_t entry)
  {
  	struct page *page;
  
  	page = find_get_page(&swapper_space, entry.val);
  
  	if (page)
  		INC_CACHE_INFO(find_success);
  
  	INC_CACHE_INFO(find_total);
  	return page;
  }
  
  /* 
   * Locate a page of swap in physical memory, reserving swap cache space
   * and reading the disk if it is not already cached.
   * A failure return means that either the page allocation failed or that
   * the swap entry is no longer in use.
   */
  struct page *read_swap_cache_async(swp_entry_t entry,
  			struct vm_area_struct *vma, unsigned long addr)
  {
  	struct page *found_page, *new_page = NULL;
  	int err;
  
  	do {
  		/*
  		 * First check the swap cache.  Since this is normally
  		 * called after lookup_swap_cache() failed, re-calling
  		 * that would confuse statistics.
  		 */
  		found_page = find_get_page(&swapper_space, entry.val);
  		if (found_page)
  			break;
  
  		/*
  		 * Get a new page to read into from swap.
  		 */
  		if (!new_page) {

  			new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE,
  								vma, addr);

  			if (!new_page)
  				break;		/* Out of memory */
  		}
  
  		/*
  		 * Associate the page with swap entry in the swap cache.
  		 * May fail (-ENOENT) if swap entry has been freed since
  		 * our caller observed it.  May fail (-EEXIST) if there
  		 * is already a page associated with this entry in the
  		 * swap cache: added by a racing read_swap_cache_async,
  		 * or by try_to_swap_out (or shmem_writepage) re-using
  		 * the just freed swap entry for an existing page.
  		 * May fail (-ENOMEM) if radix-tree node allocation failed.
  		 */
  		err = add_to_swap_cache(new_page, entry);
  		if (!err) {
  			/*
  			 * Initiate read into locked page and return.
  			 */
  			lru_cache_add_active(new_page);
  			swap_readpage(NULL, new_page);
  			return new_page;
  		}
  	} while (err != -ENOENT && err != -ENOMEM);
  
  	if (new_page)
  		page_cache_release(new_page);
  	return found_page;
  }