如何在ubuntu上默认启用透明的大页面？

$uname -a

Linux yoda 3.5.0-23-generic #35~precise1-Ubuntu SMP Fri Jan 25 17:13:26 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux

~$cd /sys/kernel/mm/transparent_hugepage/

/sys/kernel/mm/transparent_hugepage$ls

defrag enabled khugepaged

/sys/kernel/mm/transparent_hugepage$cat enabled

always [madvise] never

/sys/kernel/mm/transparent_hugepage$sudo echo always > enabled

-bash: enabled: Permission denied

/sys/kernel/mm/transparent_hugepage$sudo ls

[sudo] password for <...>:

defrag enabled khugepaged

/sys/kernel/mm/transparent_hugepage$sudo ls

defrag enabled khugepaged

/sys/kernel/mm/transparent_hugepage$sudo echo always > enabled

-bash: enabled: Permission denied

/sys/kernel/mm/transparent_hugepage$cat enabled

always [madvise] never