Record the readahead pattern in ra_flags. This info can be examined by
users via the readahead tracing/stats interfaces.
Currently 7 patterns are defined:
pattern readahead for
-----------------------------------------------------------
RA_PATTERN_INITIAL start-of-file/oversize read
RA_PATTERN_SUBSEQUENT trivial sequential read
RA_PATTERN_CONTEXT interleaved sequential read
RA_PATTERN_THRASH thrashed sequential read
RA_PATTERN_MMAP_AROUND mmap fault
RA_PATTERN_FADVISE posix_fadvise()
RA_PATTERN_RANDOM random read
CC: Ingo Molnar<mingo@xxxxxxx>
CC: Jens Axboe<jens.axboe@xxxxxxxxxx>
CC: Peter Zijlstra<a.p.zijlstra@xxxxxxxxx>
Signed-off-by: Wu Fengguang<fengguang.wu@xxxxxxxxx>