Disableing transparent hugepages (THP) on RHEL/CentOS 6

Reading time ~1 minute

How to

Environment

  • Red Hat Enterprise Linux (RHEL) 6
  • transparent hugepages (THP)
  • tuned
  • ktune

Change the kernel setting on /boot/grub/grub.conf

$ sed -i 's/quiet/quiet transparent_hugepage=never/' /boot/grub/grub.conf

reboot your system

$ reboot

check after reboot

$ grep -i never /boot/grub/grub.conf 
    kernel /boot/vmlinuz-2.6.32-358.el6.x86_64 ro root=UUID=a216d1e5-884f-4e5c-859a-6e2e2530d486 rhgb quiet transparent_hugepage=never

$ cat /sys/kernel/mm/redhat_transparent_hugepage/enabled
always [never]

when it is not taking effect

Issue

  • Unable to disable transparent hugepages (THP) even after appending “transparent_hugepage=never” to kernel command line in /boot/grub/grub.conf file.
$ grep -i never /boot/grub/grub.conf 
    kernel /boot/vmlinuz-2.6.32-358.el6.x86_64 ro root=UUID=a216d1e5-884f-4e5c-859a-6e2e2530d486 rhgb quiet transparent_hugepage=never

$ cat /sys/kernel/mm/redhat_transparent_hugepage/enabled
[always] never

$ grep -i AnonHugePages /proc/meminfo 
AnonHugePages:    206848 kB

Resolution

Create a customized tuned profile with disabled THP

$ tuned-adm  active
Current active profile: throughput-performance
Service tuned: enabled, running
Service ktune: enabled, running
$ cd /etc/tune-profiles/
$ cp -r throughput-performance throughput-performance-no-thp

$ sed -ie 's,set_transparent_hugepages always,set_transparent_hugepages never,' \
      /etc/tune-profiles/throughput-performance-no-thp/ktune.sh
$ grep set_transparent_hugepages /etc/tune-profiles/throughput-performance-no-thp/ktune.sh
        set_transparent_hugepages never
$ tuned-adm profile throughput-performance-no-thp
$ cat /sys/kernel/mm/redhat_transparent_hugepage/enabled
always [never]

Alternative: Disable tuned and ktune services.

$ service tuned stop
$ chkconfig tuned off
$ service ktune stop
$ chkconfig ktune of

or

$ tuned-adm off

Root Cause

  • The ktune service enables transparent hugepages (THP) by default for all profiles.
# cat /etc/tune-profiles/enterprise-storage/ktune.sh 
#!/bin/sh

. /etc/tune-profiles/functions

start() {
    set_cpu_governor performance
    set_transparent_hugepages always  <<<----
    disable_disk_barriers
    multiply_disk_readahead 4

    return 0
}

stop() {
    restore_cpu_governor
    restore_transparent_hugepages
    enable_disk_barriers
    restore_disk_readahead

    return 0
}

process $@

Diagnostic

  • Verify ktune and tuned services;
$ chkconfig --list |egrep -i "ktune|tuned"
ktune           0:off   1:off   2:off   3:on    4:on    5:on    6:off
tuned           0:off   1:off   2:on    3:on    4:on    5:on    6:off

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