static int
romfs_readpage(struct file *file, struct page * page)
{
	struct inode *inode = page->mapping->host;
	loff_t offset, avail, readlen;
	void *buf;
	int result = -EIO;

	page_cache_get(page);
	lock_kernel();
	buf = kmap(page);
	if (!buf)
		goto err_out;

	/* 32 bit warning -- but not for us :) */
	offset = page_offset(page);
	if (offset < i_size_read(inode)) {
		avail = inode->i_size-offset;
		readlen = min_t(unsigned long, avail, PAGE_SIZE);
		if (romfs_copyfrom(inode, buf, ROMFS_I(inode)->i_dataoffset+offset, readlen) == readlen) {
			if (readlen < PAGE_SIZE) {
				memset(buf + readlen,0,PAGE_SIZE-readlen);
			}
			SetPageUptodate(page);
			result = 0;
		}
	}

/*
 * __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;

	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;
}

/*
 * Writeback is about to end against a page which has been marked for immediate
 * reclaim.  If it still appears to be reclaimable, move it to the tail of the
 * inactive list.
 *
 * Returns zero if it cleared PG_writeback.
 */
int rotate_reclaimable_page(struct page *page)
{
	struct pagevec *pvec;
	unsigned long flags;

	if (PageLocked(page))
		return 1;
	if (PageDirty(page))
		return 1;
	if (PageActive(page))
		return 1;
	if (!PageLRU(page))
		return 1;

	page_cache_get(page);
	local_irq_save(flags);
	pvec = &__get_cpu_var(lru_rotate_pvecs);
	if (!pagevec_add(pvec, page))
		pagevec_move_tail(pvec);
	local_irq_restore(flags);

	if (!test_clear_page_writeback(page))
		BUG();

	return 0;
}

/*
 * Write a page to the server. This will be used for NFS swapping only
 * (for now), and we currently do this synchronously only.
 *
 * We are called with the page locked and we unlock it when done.
 */
static int
smb_writepage(struct page *page, struct writeback_control *wbc)
{
	struct address_space *mapping = page->mapping;
	struct inode *inode;
	unsigned long end_index;
	unsigned offset = PAGE_CACHE_SIZE;
	int err;

	BUG_ON(!mapping);
	inode = mapping->host;
	BUG_ON(!inode);

	end_index = inode->i_size >> PAGE_CACHE_SHIFT;

	/* easy case */
	if (page->index < end_index)
		goto do_it;
	/* things got complicated... */
	offset = inode->i_size & (PAGE_CACHE_SIZE-1);
	/* OK, are we completely out? */
	if (page->index >= end_index+1 || !offset)
		return 0; /* truncated - don't care */
do_it:
	page_cache_get(page);
	err = smb_writepage_sync(inode, page, 0, offset);
	SetPageUptodate(page);
	unlock_page(page);
	page_cache_release(page);
	return err;
}

/*
 * __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(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);
			SetPageLocked(page);
			SetPageSwapCache(page);
			set_page_private(page, entry.val);
			total_swapcache_pages++;
			pagecache_acct(1);
		}
		write_unlock_irq(&swapper_space.tree_lock);
		radix_tree_preload_end();
	}
	return error;
}

/**
 * get the page associated with the block inside our dedup structure
 */
struct page* dedup_get_block_page(sector_t block)
{
	struct page *res = NULL;

	// Check if the block is inside our range
	if (dedup_is_in_range(block)) {
		// Get the page pointer stored inside the dedup structure
		res = blocksArray.pages[block - start_block];
		if (res != NULL) {
			// If its not NULL, check if the page is up to date and used
			if (PageLRU(res) && PageUptodate(res)) {
				page_cache_get(res);
			}
			else {
				// Cannot use page, need to read from bdev
				blocksArray.pages[block - start_block] = NULL;
				res = NULL;
			}
		}
	}
	else
		printk("get_block_page: block not in range.\n");

	return res;
}

/*
 * 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;

	BUG_ON(!PageLocked(page));
	BUG_ON(PageSwapCache(page));
	BUG_ON(PagePrivate(page));
	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;
}

/**
 * lru_cache_add: add a page to the page lists
 * @page: the page to add
 */
void lru_cache_add(struct page *page)
{
    struct pagevec *pvec = &get_cpu_var(lru_add_pvecs);

    page_cache_get(page);
    if (!pagevec_add(pvec, page))
        __pagevec_lru_add(pvec);
    put_cpu_var(lru_add_pvecs);
}

int get_user_pages(struct task_struct *tsk, struct mm_struct *mm, unsigned long start,
		int len, int write, int force, struct page **pages, struct vm_area_struct **vmas)
{
	int i = 0;

	do {
		struct vm_area_struct *	vma;

		vma = find_extend_vma(mm, start);

		if ( !vma ||
		    (!force &&
		     	((write && (!(vma->vm_flags & VM_WRITE))) ||
		    	 (!write && (!(vma->vm_flags & VM_READ))) ) )) {
			if (i) return i;
			return -EFAULT;
		}

		spin_lock(&mm->page_table_lock);
		do {
			struct page *map;
			while (!(map = follow_page(mm, start, write))) {
				spin_unlock(&mm->page_table_lock);
				switch (handle_mm_fault(mm, vma, start, write)) {
				case 1:
					tsk->min_flt++;
					break;
				case 2:
					tsk->maj_flt++;
					break;
				case 0:
					if (i) return i;
					return -EFAULT;
				default:
					if (i) return i;
					return -ENOMEM;
				}
				spin_lock(&mm->page_table_lock);
			}
			if (pages) {
				pages[i] = get_page_map(map);
				/* FIXME: call the correct function,
				 * depending on the type of the found page
				 */
				if (pages[i])
					page_cache_get(pages[i]);
			}
			if (vmas)
				vmas[i] = vma;
			i++;
			start += PAGE_SIZE;
			len--;
		} while(len && start < vma->vm_end);
		spin_unlock(&mm->page_table_lock);
	} while(len);
	return i;
}

void fastcall lru_cache_add_active(struct page *page)
{
	struct pagevec *pvec = &get_cpu_var(lru_add_active_pvecs);

	page_cache_get(page);
	if (!pagevec_add(pvec, page))
		__pagevec_lru_add_active(pvec);
	put_cpu_var(lru_add_active_pvecs);
}

void __lru_cache_add(struct page *page, enum lru_list lru)
{
	struct pagevec *pvec = &get_cpu_var(lru_add_pvecs)[lru];

	page_cache_get(page);
	if (!pagevec_add(pvec, page))
		____pagevec_lru_add(pvec, lru);
	put_cpu_var(lru_add_pvecs);
}

/*
 * Order of operations is important: flush the pagevec when it's already
 * full, not when adding the last page, to make sure that last page is
 * not added to the LRU directly when passed to this function. Because
 * mark_page_accessed() (called after this when writing) only activates
 * pages that are on the LRU, linear writes in subpage chunks would see
 * every PAGEVEC_SIZE page activated, which is unexpected.
 */
void __lru_cache_add(struct page *page, enum lru_list lru)
{
	struct pagevec *pvec = &get_locked_var(swapvec_lock, lru_add_pvecs)[lru];

	page_cache_get(page);
	if (!pagevec_space(pvec))
		__pagevec_lru_add(pvec, lru);
	pagevec_add(pvec, page);
	put_locked_var(swapvec_lock, lru_add_pvecs);
}

/**
 * __lru_cache_add:page加入到lru类型的lru_add_pvecs页缓存中
 */
void __lru_cache_add(struct page *page, enum lru_list lru)
{
	struct pagevec *pvec = &get_cpu_var(lru_add_pvecs)[lru];

	page_cache_get(page);
	/*加入页缓存中,当也缓存满时,才加入到page对应
	 * 的zone的lru链表中*/
	if (!pagevec_add(pvec, page))
		____pagevec_lru_add(pvec, lru);
	put_cpu_var(lru_add_pvecs);
}

/**
 * lru_cache_add: add a page to the page lists
 * @page: the page to add
 */
void fastcall lru_cache_add(struct page *page)
{
	struct pagevec *pvec = &get_cpu_var(lru_add_pvecs);

	page_cache_get(page);
    // dyc: if no space left in pvec, add all pages into zone's inactive list
	if (!pagevec_add(pvec, page)) {
		__pagevec_lru_add(pvec);
    }
	put_cpu_var(lru_add_pvecs);
}

/*
 * We are called with the page locked and we unlock it when done.
 */
static int
smb_readpage(struct file *file, struct page *page)
{
	int		error;
	struct dentry  *dentry = file->f_path.dentry;

	page_cache_get(page);
	error = smb_readpage_sync(dentry, page);
	page_cache_release(page);
	return error;
}

int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
		unsigned long start, int len, int write, int force,
		struct page **pages, struct vm_area_struct **vmas)
{
	int i;
	static struct vm_area_struct dummy_vma;

	for (i = 0; i < len; i++) {
		if (pages) {
			pages[i] = virt_to_page(start);
			if (pages[i])
				page_cache_get(pages[i]);
		}
		if (vmas)
			vmas[i] = &dummy_vma;
		start += PAGE_SIZE;
	}
	return(i);
}

long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
		      unsigned long start, unsigned long nr_pages,
		      unsigned int foll_flags, struct page **pages,
		      struct vm_area_struct **vmas, int *nonblocking)
{
	struct vm_area_struct *vma;
	unsigned long vm_flags;
	int i;

	/* calculate required read or write permissions.
	 * If FOLL_FORCE is set, we only require the "MAY" flags.
	 */
	vm_flags  = (foll_flags & FOLL_WRITE) ?
			(VM_WRITE | VM_MAYWRITE) : (VM_READ | VM_MAYREAD);
	vm_flags &= (foll_flags & FOLL_FORCE) ?
			(VM_MAYREAD | VM_MAYWRITE) : (VM_READ | VM_WRITE);

	for (i = 0; i < nr_pages; i++) {
		vma = find_vma(mm, start);
		if (!vma)
			goto finish_or_fault;

		/* protect what we can, including chardevs */
		if ((vma->vm_flags & (VM_IO | VM_PFNMAP)) ||
		    !(vm_flags & vma->vm_flags))
			goto finish_or_fault;

		if (pages) {
			pages[i] = virt_to_page(start);
			if (pages[i])
				page_cache_get(pages[i]);
		}
		if (vmas)
			vmas[i] = vma;
		start = (start + PAGE_SIZE) & PAGE_MASK;
	}

	return i;

finish_or_fault:
	return i ? : -EFAULT;
}

void nilfs_btnode_delete(struct buffer_head *bh)
{
	struct address_space *mapping;
	struct page *page = bh->b_page;
	pgoff_t index = page_index(page);
	int still_dirty;

	page_cache_get(page);
	lock_page(page);
	wait_on_page_writeback(page);

	nilfs_forget_buffer(bh);
	still_dirty = PageDirty(page);
	mapping = page->mapping;
	unlock_page(page);
	page_cache_release(page);

	if (!still_dirty && mapping)
		invalidate_inode_pages2_range(mapping, index, index);
}

/**
 * nfs_create_request - Create an NFS read/write request.
 * @file: file descriptor to use
 * @inode: inode to which the request is attached
 * @page: page to write
 * @offset: starting offset within the page for the write
 * @count: number of bytes to read/write
 *
 * The page must be locked by the caller. This makes sure we never
 * create two different requests for the same page, and avoids
 * a possible deadlock when we reach the hard limit on the number
 * of dirty pages.
 * User should ensure it is safe to sleep in this function.
 */
struct nfs_page *
nfs_create_request(struct nfs_open_context *ctx, struct inode *inode,
		   struct page *page,
		   unsigned int offset, unsigned int count)
{
	struct nfs_server *server = NFS_SERVER(inode);
	struct nfs_page		*req;

	/* Deal with hard limits.  */
	for (;;) {
		/* try to allocate the request struct */
		req = nfs_page_alloc();
		if (req != NULL)
			break;

		/* Try to free up at least one request in order to stay
		 * below the hard limit
		 */
		if (signalled() && (server->flags & NFS_MOUNT_INTR))
			return ERR_PTR(-ERESTARTSYS);
		yield();
	}

	/* Initialize the request struct. Initially, we assume a
	 * long write-back delay. This will be adjusted in
	 * update_nfs_request below if the region is not locked. */
	req->wb_page    = page;
	atomic_set(&req->wb_complete, 0);
	req->wb_index	= page->index;
	page_cache_get(page);
	BUG_ON(PagePrivate(page));
	BUG_ON(!PageLocked(page));
	BUG_ON(page->mapping->host != inode);
	req->wb_offset  = offset;
	req->wb_pgbase	= offset;
	req->wb_bytes   = count;
	atomic_set(&req->wb_count, 1);
	req->wb_context = get_nfs_open_context(ctx);

	return req;
}

static int
HgfsReadpage(struct file *file, // IN:     File to read from
             struct page *page) // IN/OUT: Page to write to
{
   int result = 0;
   HgfsHandle handle;

   ASSERT(file);
   ASSERT(file->f_dentry);
   ASSERT(file->f_dentry->d_inode);
   ASSERT(page);

   handle = FILE_GET_FI_P(file)->handle;
   LOG(6, (KERN_WARNING "VMware hgfs: HgfsReadPage: reading from handle %u\n",
           handle));

   page_cache_get(page);
   result = HgfsDoReadpage(handle, page, 0, PAGE_CACHE_SIZE);
   page_cache_release(page);
   compat_unlock_page(page);
   return result;
}