/*
 * add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
 * but sets SwapCache flag and private instead of mapping and index.
 */
int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
{
	int error;

	VM_BUG_ON(!PageLocked(page));
	VM_BUG_ON(PageSwapCache(page));
	VM_BUG_ON(!PageSwapBacked(page));

	error = radix_tree_preload(gfp_mask);
	if (!error) {
		page_cache_get(page);
		SetPageSwapCache(page);
		set_page_private(page, entry.val);

		spin_lock_irq(&swapper_space.tree_lock);
		error = radix_tree_insert(&swapper_space.page_tree,
						entry.val, page);
		if (likely(!error)) {
			total_swapcache_pages++;
			__inc_zone_page_state(page, NR_FILE_PAGES);
			INC_CACHE_INFO(add_total);
		}
		spin_unlock_irq(&swapper_space.tree_lock);
		radix_tree_preload_end();

		if (unlikely(error)) {
			set_page_private(page, 0UL);
			ClearPageSwapCache(page);
			page_cache_release(page);
		}
	}
	return error;
}

/*
 * __add_to_swap_cache resembles add_to_page_cache_locked 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)
{
	int error;

	VM_BUG_ON(!PageLocked(page));
	VM_BUG_ON(PageSwapCache(page));
	VM_BUG_ON(!PageSwapBacked(page));

	page_cache_get(page);
	SetPageSwapCache(page);
	set_page_private(page, entry.val);

	spin_lock_irq(&swapper_space.tree_lock);
	error = radix_tree_insert(&swapper_space.page_tree, entry.val, page);
	if (likely(!error)) {
		total_swapcache_pages++;
		__inc_zone_page_state(page, NR_FILE_PAGES);
		INC_CACHE_INFO(add_total);
	}
	spin_unlock_irq(&swapper_space.tree_lock);

	if (unlikely(error)) {
		/*
		 * Only the context which have set SWAP_HAS_CACHE flag
		 * would call add_to_swap_cache().
		 * So add_to_swap_cache() doesn't returns -EEXIST.
		 */
		VM_BUG_ON(error == -EEXIST);
		set_page_private(page, 0UL);
		ClearPageSwapCache(page);
		page_cache_release(page);
	}

	return error;
}

/**
 * __delete_from_swap_cache:page从交换区高速缓存中删去
 */
void __delete_from_swap_cache(struct page *page)
{
	VM_BUG_ON(!PageLocked(page));
	VM_BUG_ON(!PageSwapCache(page));
	VM_BUG_ON(PageWriteback(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);
}

/*
 * 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--;
	pagecache_acct(-1);
	INC_CACHE_INFO(del_total);
}

/*
 * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
 * but sets SwapCache flag and private instead of mapping and index.
 */
int __add_to_swap_cache(struct page *page, swp_entry_t entry)
{
	int error, i, nr = hpage_nr_pages(page);
	struct address_space *address_space;
	pgoff_t idx = swp_offset(entry);

	VM_BUG_ON_PAGE(!PageLocked(page), page);
	VM_BUG_ON_PAGE(PageSwapCache(page), page);
	VM_BUG_ON_PAGE(!PageSwapBacked(page), page);

	page_ref_add(page, nr);
	SetPageSwapCache(page);

	address_space = swap_address_space(entry);
	spin_lock_irq(&address_space->tree_lock);
	for (i = 0; i < nr; i++) {
		set_page_private(page + i, entry.val + i);
		error = radix_tree_insert(&address_space->page_tree,
					  idx + i, page + i);
		if (unlikely(error))
			break;
	}
	if (likely(!error)) {
		address_space->nrpages += nr;
		__mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, nr);
		ADD_CACHE_INFO(add_total, nr);
	} else {
		/*
		 * Only the context which have set SWAP_HAS_CACHE flag
		 * would call add_to_swap_cache().
		 * So add_to_swap_cache() doesn't returns -EEXIST.
		 */
		VM_BUG_ON(error == -EEXIST);
		set_page_private(page + i, 0UL);
		while (i--) {
			radix_tree_delete(&address_space->page_tree, idx + i);
			set_page_private(page + i, 0UL);
		}
		ClearPageSwapCache(page);
		page_ref_sub(page, nr);
	}
	spin_unlock_irq(&address_space->tree_lock);

	return error;
}

/*
 * 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)
{
    swp_entry_t entry;
    struct address_space *address_space;

    VM_BUG_ON_PAGE(!PageLocked(page), page);
    VM_BUG_ON_PAGE(!PageSwapCache(page), page);
    VM_BUG_ON_PAGE(PageWriteback(page), page);

    entry.val = page_private(page);
    address_space = swap_address_space(entry);
    radix_tree_delete(&address_space->page_tree, page_private(page));
    set_page_private(page, 0);
    ClearPageSwapCache(page);
    address_space->nrpages--;
    __dec_zone_page_state(page, NR_FILE_PAGES);
    INC_CACHE_INFO(del_total);
}

/*
 * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
 * but sets SwapCache flag and private instead of mapping and index.
 */
int __add_to_swap_cache(struct page *page, swp_entry_t entry)
{
    int error;
    struct address_space *address_space;

    VM_BUG_ON_PAGE(!PageLocked(page), page);
    VM_BUG_ON_PAGE(PageSwapCache(page), page);
    VM_BUG_ON_PAGE(!PageSwapBacked(page), page);

    get_page(page);
    SetPageSwapCache(page);
    set_page_private(page, entry.val);

    address_space = swap_address_space(entry);
    spin_lock_irq(&address_space->tree_lock);
    error = radix_tree_insert(&address_space->page_tree,
                              entry.val, page);
    if (likely(!error)) {
        address_space->nrpages++;
        __inc_zone_page_state(page, NR_FILE_PAGES);
        INC_CACHE_INFO(add_total);
    }
    spin_unlock_irq(&address_space->tree_lock);

    if (unlikely(error)) {
        /*
         * Only the context which have set SWAP_HAS_CACHE flag
         * would call add_to_swap_cache().
         * So add_to_swap_cache() doesn't returns -EEXIST.
         */
        VM_BUG_ON(error == -EEXIST);
        set_page_private(page, 0UL);
        ClearPageSwapCache(page);
        put_page(page);
    }

    return error;
}

/*
 * 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)
{
	struct address_space *address_space;
	int i, nr = hpage_nr_pages(page);
	swp_entry_t entry;
	pgoff_t idx;

	VM_BUG_ON_PAGE(!PageLocked(page), page);
	VM_BUG_ON_PAGE(!PageSwapCache(page), page);
	VM_BUG_ON_PAGE(PageWriteback(page), page);

	entry.val = page_private(page);
	address_space = swap_address_space(entry);
	idx = swp_offset(entry);
	for (i = 0; i < nr; i++) {
		radix_tree_delete(&address_space->page_tree, idx + i);
		set_page_private(page + i, 0);
	}
	ClearPageSwapCache(page);
	address_space->nrpages -= nr;
	__mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, -nr);
	ADD_CACHE_INFO(del_total, nr);
}