Disabling Transparent HugePages

Disabling Transparent HugePages (RHEL6/OL6)

Starting from RHEL6/OL6, Transparent HugePages are implemented and enabled by default. They are meant to improve memory management by allowing HugePages to be allocated dynamically by the "khugepaged" kernel thread, rather than at boot time like conventional HugePages. That sounds like a good idea, but unfortunately Transparent HugePages don't play well with Oracle databases and are associated with node reboots in RAC installations and performance problems on both single instance and RAC installations. As a result Oracle recommends disabling Transparent HugePages on all servers running Oracle databases, as described in this MOS note.

ALERT: Disable Transparent HugePages on SLES11, RHEL6, OEL6 and UEK2 Kernels [ID 1557478.1]
You can check the current setting using the following command, which is displaying the default value of "enabled=[always]".

# cat /sys/kernel/mm/transparent_hugepage/enabled
[always] madvise never
#
The preferred method to disable Transparent HugePages is to add "transparent_hugepage=never" to the kernel boot line in the "/etc/grub.conf" file.

title Oracle Linux Server (2.6.39-400.24.1.el6uek.x86_64)
root (hd0,0)
kernel /vmlinuz-2.6.39-400.24.1.el6uek.x86_64 ro root=/dev/mapper/vg_ol6112-lv_root rd_NO_LUKS  KEYBOARDTYPE=pc KEYTABLE=uk
LANG=en_US.UTF-8 rd_NO_MD SYSFONT=latarcyrheb-sun16  rd_NO_DM rd_LVM_LV=vg_ol6112/lv_swap rd_LVM_LV=vg_ol6112/lv_root rhgb quiet numa=off
transparent_hugepage=never
initrd /initramfs-2.6.39-400.24.1.el6uek.x86_64.img
The server must be rebooted for this to take effect.

Alternatively, add the following lines into the "/etc/rc.local" file and reboot the server.

if test -f /sys/kernel/mm/transparent_hugepage/enabled; then
echo never > /sys/kernel/mm/transparent_hugepage/enabled
fi
if test -f /sys/kernel/mm/transparent_hugepage/defrag; then
echo never > /sys/kernel/mm/transparent_hugepage/defrag
fi
Whichever method you choose, remember to check the change has work after reboot.

# cat /sys/kernel/mm/transparent_hugepage/enabled
always madvise [never]
#
With Transparent HugePages disabled, you should proceed to configure conventional HugePages, as described above.