enable ksm
make default readahead size a kernel parameter
From: Nikanth Karthikesan <knikanth@suse.de>

Add new kernel parameter "readahead", which would be used instead of the
value of VM_MAX_READAHEAD. If the parameter is not specified, the default
of 128kb would be used.

CC: Ankit Jain <radical@gmail.com>
CC: Dave Chinner <david@fromorbit.com>
CC: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>
Signed-off-by: Nikanth Karthikesan <knikanth@suse.de>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Dan Trifan <jimsth@gmail.com>

Conflicts:
	include/linux/mm.h
mm: finetune the filesystem dynamic read-ahead

Signed-off-by: Dan Trifan <jimsth@gmail.com>

Conflicts:
	include/linux/mm.h

Conflicts:
	include/linux/mm.h

Conflicts:
	include/linux/mm.h
mm: optimize Kernel Samepage Merging(KSM)

Signed-off-by: Dan Trifan <jimsth@gmail.com>