readahead cleanups and interleaved readahead take 2

Linus,

To save you from some merge conflicts, I rebased this readahead patchset to 2.6.22-git5.

The following patches are based on yesterday's discussions, compiled and tested OK.

smaller file_ra_state:
[PATCH 1/8] compacting file_ra_state
[PATCH 2/8] mmap read-around simplification
[PATCH 3/8] combine file_ra_state.prev_index/prev_offset into prev_pos

code cleanups:
[PATCH 4/8] trivial filemap.c cleanups
[PATCH 5/8] remove several readahead macros
[PATCH 6/8] remove the limit max_sectors_kb imposed on max_readahead_kb

support of interleaved reads:
[PATCH 7/8] introduce radix_tree_scan_hole() [PATCH 8/8] basic support of interleaved reads

The diffstat is

 block/ll_rw_blk.c          |    9 -----
 fs/ext3/dir.c              |    2 -
 fs/ext4/dir.c              |    2 -
 fs/splice.c                |    2 -
 include/linux/fs.h         |   14 +++-----
 include/linux/mm.h         |    2 -
 include/linux/radix-tree.h |    2 +
 lib/radix-tree.c           |   34 ++++++++++++++++++++
 mm/filemap.c               |   31 +++++++++---------
 mm/readahead.c             |   58 +++++++++++++++++++----------------
 10 files changed, 92 insertions(+), 64 deletions(-)

Regards,
Fengguang Wu
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