Re: [PATCH 02/10] xfs: separate buffer indexing from block map

Mark Tinguely
2012-04-30T19:28:44Z

On 04/24/12 01:33, Dave Chinner wrote:
> From: Dave Chinner<dchinner@redhat.com>
>
> To support discontiguous buffers in the buffer cache, we need to
> separate the cache index variables from the I/O map. While this is
> currently a 1:1 mapping, discontiguous buffer support will break
> this relationship.
>
> However, for caching purposes, we can still treat them the same as a
> contiguous buffer - the block number of the first block and the
> length of the buffer - as that is still a unique representation.
> Also, the only way we will ever access the discontiguous regions of
> buffers is via bulding the complete buffer in the first place, so
> using the initial block number and entire buffer length is a sane
> way to index the buffers.
>
> Add a block mapping vector construct to the xfs_buf and use it in
> the places where we are doing IO instead of the current
> b_bn/b_length variables.
>
> Signed-off-by: Dave Chinner<dchinner@redhat.com>
...
> +struct xfs_buf_map {
> + xfs_daddr_t bm_bn; /* block number for I/O */
> + int bm_len; /* size of I/O */
> +};
> +
> typedef struct xfs_buf {
> /*
> * first cacheline holds all the fields needed for an uncontended cache
> @@ -107,7 +114,7 @@ typedef struct xfs_buf {
> * fast-path on locking.
> */
> struct rb_node b_rbnode; /* rbtree node */
> - xfs_daddr_t b_bn; /* block number for I/O */
> + xfs_daddr_t b_bn; /* block number of buffer */
> int b_length; /* size of buffer in BBs */

Looks good.
Do you plan to eventually remove b_bn and b_length from xfs_buf?

Reviewed-by: Mark Tinguely <tinguely@sgi.com>