Bumping the read-ahead count once more, to value equivalent to 512 KiB on most system, based on benchmark results on a low-end fibre channel SAN under VMWare:
Bumping the read-ahead count once more, to value equivalent to 512 KiB on
most system, based on benchmark results on a low-end fibre channel SAN
under VMWare:

vfs.read_max		read performance
8  (historical default)	83 MB/s
16 (recent bump)	131 MB/s
32 (this version)	152 MB/s
64			157 MB/s

(results are +/- 3 MB/s)

As read-ahead is heuristic, based on past IO requests, it shouldn't be
problematic. The new default is still smaller then in other OSes.

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