xfs: pack xfs_buf structure more tightly

#define XB_PAGES	2

typedef struct xfs_buf {

	/*

	 * first cacheline holds all the fields needed for an uncontended cache

	 * hit to be fully processed. The semaphore straddles the cacheline

	 * boundary, but the counter and lock sits on the first cacheline,

	 * which is the only bit that is touched if we hit the semaphore

	 * fast-path on locking.

	 */

	struct rb_node		b_rbnode;	/* rbtree node */

	xfs_off_t		b_file_offset;	/* offset in file */

	size_t			b_buffer_length;/* size of buffer in bytes */

	atomic_t		b_hold;		/* reference count */

	xfs_buf_flags_t		b_flags;	/* status flags */

	struct semaphore	b_sema;		/* semaphore for lockables */

	unsigned long		b_queuetime;	/* time buffer was queued */

	atomic_t		b_pin_count;	/* pin count */

	wait_queue_head_t	b_waiters;	/* unpin waiters */

	struct list_head	b_list;

	xfs_buf_flags_t		b_flags;	/* status flags */

	struct rb_node		b_rbnode;	/* rbtree node */

	struct xfs_perag	*b_pag;		/* contains rbtree root */

	xfs_buftarg_t		*b_target;	/* buffer target (device) */

	atomic_t		b_hold;		/* reference count */

	xfs_daddr_t		b_bn;		/* block number for I/O */

	xfs_off_t		b_file_offset;	/* offset in file */

	size_t			b_buffer_length;/* size of buffer in bytes */

	size_t			b_count_desired;/* desired transfer size */

	void			*b_addr;	/* virtual address of buffer */

	struct work_struct	b_iodone_work;

	atomic_t		b_io_remaining;	/* #outstanding I/O requests */

	xfs_buf_iodone_t	b_iodone;	/* I/O completion function */

	xfs_buf_relse_t		b_relse;	/* releasing function */

	struct completion	b_iowait;	/* queue for I/O waiters */

	void			*b_fspriv;

	void			*b_fspriv2;

	unsigned short		b_error;	/* error code on I/O */

	unsigned int		b_page_count;	/* size of page array */

	unsigned int		b_offset;	/* page offset in first page */

	struct page		**b_pages;	/* array of page pointers */

	struct page		*b_page_array[XB_PAGES]; /* inline pages */

	unsigned long		b_queuetime;	/* time buffer was queued */

	atomic_t		b_pin_count;	/* pin count */

	atomic_t		b_io_remaining;	/* #outstanding I/O requests */

	unsigned int		b_page_count;	/* size of page array */

	unsigned int		b_offset;	/* page offset in first page */

	unsigned short		b_error;	/* error code on I/O */

#ifdef XFS_BUF_LOCK_TRACKING

	int			b_last_holder;

#endif