readahead stats/tracing, backwards prefetching and more (v2)

Andrew,

This is what the bit fields look like :)

Changes since v1:
- use bit fields: pattern, for_mmap, for_metadata, lseek
- comment the various readahead patterns
- drop boot options "readahead=" and "readahead_stats="
- add for_metadata
- add snapping to EOF

[PATCH 1/9] block: limit default readahead size for small devices [PATCH 2/9] readahead: snap readahead request to EOF [PATCH 3/9] readahead: record readahead patterns
[PATCH 4/9] readahead: tag mmap page fault call sites [PATCH 5/9] readahead: tag metadata call sites
[PATCH 6/9] readahead: add /debug/readahead/stats
[PATCH 7/9] readahead: add vfs/readahead tracing event [PATCH 8/9] readahead: basic support for backwards prefetching [PATCH 9/9] readahead: dont do start-of-file readahead after lseek()

 block/genhd.c              |   20 ++
 fs/ext3/dir.c              |    1 
 fs/ext4/dir.c              |    1 
 fs/read_write.c            |    3 
 include/linux/fs.h         |   41 +++++
 include/linux/mm.h         |    4 
 include/trace/events/vfs.h |   64 ++++++++
 mm/Kconfig                 |   15 ++
 mm/filemap.c               |    9 -
 mm/readahead.c             |  257 ++++++++++++++++++++++++++++++++++-
 10 files changed, 404 insertions(+), 11 deletions(-)

Thanks,
Fengguang