page cache: Rearrange address_space

				loff_t pos, unsigned len, unsigned copied,

				struct page *page, void *fsdata);

/**

 * struct address_space - Contents of a cacheable, mappable object.

 * @host: Owner, either the inode or the block_device.

 * @i_pages: Cached pages.

 * @gfp_mask: Memory allocation flags to use for allocating pages.

 * @i_mmap_writable: Number of VM_SHARED mappings.

 * @i_mmap: Tree of private and shared mappings.

 * @i_mmap_rwsem: Protects @i_mmap and @i_mmap_writable.

 * @nrpages: Number of page entries, protected by the i_pages lock.

 * @nrexceptional: Shadow or DAX entries, protected by the i_pages lock.

 * @writeback_index: Writeback starts here.

 * @a_ops: Methods.

 * @flags: Error bits and flags (AS_*).

 * @wb_err: The most recent error which has occurred.

 * @private_lock: For use by the owner of the address_space.

 * @private_list: For use by the owner of the address_space.

 * @private_data: For use by the owner of the address_space.

 */

struct address_space {

	struct inode		*host;		/* owner: inode, block_device */

	struct radix_tree_root	i_pages;	/* cached pages */

	atomic_t		i_mmap_writable;/* count VM_SHARED mappings */

	struct rb_root_cached	i_mmap;		/* tree of private and shared mappings */

	struct rw_semaphore	i_mmap_rwsem;	/* protect tree, count, list */

	/* Protected by the i_pages lock */

	unsigned long		nrpages;	/* number of total pages */

	/* number of shadow or DAX exceptional entries */

	struct inode		*host;

	struct xarray		i_pages;

	gfp_t			gfp_mask;

	atomic_t		i_mmap_writable;

	struct rb_root_cached	i_mmap;

	struct rw_semaphore	i_mmap_rwsem;

	unsigned long		nrpages;

	unsigned long		nrexceptional;

	pgoff_t			writeback_index;/* writeback starts here */

	const struct address_space_operations *a_ops;	/* methods */

	unsigned long		flags;		/* error bits */

	spinlock_t		private_lock;	/* for use by the address_space */

	gfp_t			gfp_mask;	/* implicit gfp mask for allocations */

	struct list_head	private_list;	/* for use by the address_space */

	void			*private_data;	/* ditto */

	pgoff_t			writeback_index;

	const struct address_space_operations *a_ops;

	unsigned long		flags;

	errseq_t		wb_err;

	spinlock_t		private_lock;

	struct list_head	private_list;

	void			*private_data;

} __attribute__((aligned(sizeof(long)))) __randomize_layout;

	/*

	 * On most architectures that alignment is already the case; but