disable transparent hugepages

  • We are installing SAP HANA in a RAID machine. As part of the installation step, it is mentioned that,

     To disable the usage of transparent hugepages set the kernel settings 
     at runtime with echo never > /sys/kernel/mm/transparent_hugepage/enabled 
    

    So instead of runtime, if I wanted to make this a permanent change, should I add the above line inside /proc/vmstat file?

    Note that if you're using some of the solutions mentioned here, on a system that also runs 'tuned', tuned may override those solutions. See here for more info: https://bugzilla.redhat.com/show_bug.cgi?id=1189868

  • slm

    slm Correct answer

    7 years ago

    To make options such as this permanent you'll typically add them to the file /etc/sysctl.conf. You can see a full list of the options available using this command:

    $ sysctl -a
    

    Example

    $ sudo sysctl -a | head -5
    kernel.sched_child_runs_first = 0
    kernel.sched_min_granularity_ns = 6000000
    kernel.sched_latency_ns = 18000000
    kernel.sched_wakeup_granularity_ns = 3000000
    kernel.sched_shares_ratelimit = 750000
    

    You can look for hugepage in the output like so:

    $ sudo sysctl -a | grep hugepage
    vm.nr_hugepages = 0
    vm.nr_hugepages_mempolicy = 0
    vm.hugepages_treat_as_movable = 0
    vm.nr_overcommit_hugepages = 0
    

    It's not there?

    However looking through the output I did not see transparent_hugepage. Googling a bit more I did come across this Oracle page which discusses this very topic. The page is titled: Configuring HugePages for Oracle on Linux (x86-64).

    Specifically on that page they mention how to disable the hugepage feature.

    excerpt

    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 you can add the command to your /etc/rc.local file.

    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
    

    I think I would go with the 2nd option, since the first will be at risk of getting unset when you upgrade from one kernel to the next.

    You can confirm that it worked with the following command after rebooting:

    $ cat /sys/kernel/mm/transparent_hugepage/enabled
    always madvise [never]
    

    You can make the first option survive kernel updates by adding transparent_hugepage=never to the GRUB_CMDLINE_LINUX_DEFAULT option in /etc/default/grub on most distributions.

    If the output of ``cat /sys/kernel/mm/transparent_hugepage/enabled`` is ``[always] madvise never``, then the status is ``always`` or that it is enabled (note the ``[]`` brackets around ``always``)

    Don't confuse hugepages and transparent hugepages. The latter can cause many issues, mainly high CPU usage while constantly trying to defragment memory and convert normal 4kB pages into huge 2MB pages.

    @Rwky doesn't seem to work on EC2 instances, for some reason.

    @Rwky -- when tweaking as per your suggestion - I'd emphasize the next action after saving the file is to execute `sudo update-grub` to get the new settings "written in stone". +1 for pointing the grub file line.

    VERY important to heed @Marki555 warning.

    An update for those on EC2, cloudimg adds the file /etc/default/grub.d/50-cloudimg-settings.cfg which overrides the settings in /etc/default/grub adding a file /etc/default/grub.d/99-transparent-hugepage.cfg with the content GRUB_CMDLINE_LINUX_DEFAULT="$GRUB_CMDLINE_LINUX_DEFAULT transparent_hugepage=never" will solve this.

    After adding a file /etc/default/grub.d/99-transparent-hugepage.cfg with the content GRUB_CMDLINE_LINUX_DEFAULT="$GRUB_CMDLINE_LINUX_DEFAULT transparent_hugepage=never" as @Rwky mentioned, run grub-mkconfig -o /boot/grub/grub.cfg to generate the updated grub.cfg. After a restart, cat /proc/cmdline will contain transparent_hugepage=never

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Content dated before 6/26/2020 9:53 AM