LU-618 llite: IO accounting of page read

LU-618 llite: IO accounting of page read

When CONFIG_TASK_IO_ACCOUNTING is used with Lustre, writes are
accounted for but not read.

The accounting is normally done in the kernel for page writeback
and readahead functionlity, Therefore, as Lustre implements its
own readahead, it must also maintain its own accounting on read
(but not for write)

Lustre-change: https://review.whamcloud.com/1636
Lustre-commit: 48de9b195d71cb57ee50636d75c59d78ee068cee

Change-Id: I19f330be65324a8da002f9d61cb9262345ecb012
Signed-off-by: Hongchao Zhang <hongchao.zhang@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-on: https://review.whamcloud.com/30570
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>