Disabling transparent hugepages (THP) on Red Hat Enterprise Linux 6 is not taking effect.

​

環境

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

問題

• Unable to disable transparent hugepages (THP) even after appending "transparent_hugepage=never" to kernel command line in /boot/grub/grub.conf file.

  Eg:

​​Raw​​

# 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
      

決議

Create a customized tuned profile with disabled THP

With this resolution we will create a customized version of the currently running profile. The customized version will disable THP.

Find out which profile is active, create a copy. In the following example we currently use the ​

​throughput-performance​

​ profile:

$ 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
      

We will now disable THP in the new profile and activate the new profile:

$ 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]
      

We will also have to add the ​

​transparent_hugepage=never​

​ parameter to the kernel line ​

​/etc/grub.conf​

​ to ensure that when the system is booted applications already do not request THP, for example:

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

The system should then be rebooted.

Alternative Resolution: Disable ​

​tuned​

​ and ​

​ktune​

​ services.

This resolution will disable the tuned/ktune services.

# service tuned stop
# chkconfig tuned off
# service ktune stop
# chkconfig ktune off
      

OR

# tuned-adm off
      

Note: The ​

​tuned-adm​

​ command will revert all your settings to what they were before tuned started and disable the tuning services from running at boot.

• Append "transparent_hugepage=never" to kernel command line in /boot/grub/grub.conf file.

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

• Reboot the server for changes to take effect.

# reboot
      

根源

• 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 $@
      

• Any time a tuned profile is enabled, whether at bootup via an init.d service, or manually at the command line, transparent hugepages (THP) gets re-enabled.

診斷步驟

• 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
      

• When ​

  ​transparent_hugepage=never​

  ​ is appended to ​

  ​/boot/grub/grub.conf​

  ​ and the system is rebooted, the ​

  ​/sys/kernel/mm/transparent_hugepage/defrag​

  ​ option may still be enabled (ie: set to ​

  ​always​

  ​). This can safely be ignored as THP is disabled, and THP defrag will not come into effect:

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

cat /sys/kernel/mm/transparent_hugepage/defrag
[always] never