I came across this one recently…
|[root@someServer ~]# grep Huge /proc/meminfo|
Starting with RedHat6, OL6, SLES11 and UEK2 kernels, Transparent HugePages are implemented and enabled (default) in an attempt to improve the memory management. Transparent HugePages are similar to the HugePages that have been available in previous Linux releases. The main difference is that the Transparent HugePages are set up dynamically at run time by the khugepaged thread in kernel while the regular HugePages had to be preallocated at the boot up time.
Because Transparent HugePages are known to cause unexpected node reboots and performance problems with RAC, Oracle strongly advises to disable the use of Transparent HugePages. In addition, Transparent Hugepages may cause problems even in a single-instance database environment with unexpected performance problems or delays. As such, Oracle recommends disabling Transparent HugePages on all Database servers running Oracle.
# cat /sys/kernel/mm/*transparent_hugepage/enabled
To disable Transparent HugePages boot time either one of the following 2 methods may be used:
Add the following to the kernel boot line in /etc/grub.conf (a symlink to /boot/grub/grub.conf) and reboot the server (this is the preferred method):
Once modified the line will read similar to the following example:
title Oracle Linux Server (2.6.32-300.25.1.el6uek.x86_64)
kernel /vmlinuz-2.6.32-300.25.1.el6uek.x86_64 ro root=LABEL=/ transparent_hugepage=never
Add the following lines in /etc/rc.local and reboot the server:
if test -f /sys/kernel/mm/transparent_hugepage/enabled;
echo never > /sys/kernel/mm/transparent_hugepage/enabled
if test -f /sys/kernel/mm/transparent_hugepage/defrag;
echo never > /sys/kernel/mm/transparent_hugepage/defrag
Please change the file path for RHEL kernel to /sys/kernel/mm/redhat_transparent_hugepage/ accordingly.
So, there you have it.