Now that we lifts readahead size from 128KB to 512KB,
the MMAP_LOTSAMISS shall be shrinked accordingly.
We shrink it a bit more, so that for sparse random access patterns,
only 10*512KB or ~5MB memory will be wasted, instead of the previous
100*128KB or ~12MB. The new threshold "10" is still big enough to avoid
turning off read-around for typical executable/lib page faults.
CC: Nick Piggin<npiggin@xxxxxxx>
Signed-off-by: Wu Fengguang<fengguang.wu@xxxxxxxxx>