[RFC, PATCH 0/12] xfs: compound buffers for directory blocks

[Christoph Hellwig]

I've been really busy the last days and only managed to look over this
a bit while waiting for compiles and benchmarks.

The only really major comment I have is that I start to really dislike
the way struct xfs_bmbt_irec is used in the compound buffers.  The
XFS_EXT_DADDR flag basically gives the data types in there a totally
different meaning and is really confusing for anyone reading the code:
either we're using a "normal" one passes in from the directory code,
or an artificial one used internally, which uses different units.

I suspect we'd really be much better off introducing a new, smaller type
here, especially as it's only seen inside the buffer code:

struct xfs_buf_map {
	sector_t	bm_bno;
	size_t		bm_len;
};

any use it consistently, that is also use it to replace
b_file_offset/b_buffer_length and b_bn.    This will also make my number
two suggestion a lot cleaner, that is make sure the new abstraction can
be implemented for reading/writing log buffers that wrap around, and
allow to kill off xfs_buf_associate_memory entirely.