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Disable Transparent Huge Pages (THP)

On this page

  • Create a Service File
  • Using tuned and ktune

Transparent Huge Pages (THP) is a Linux memory management system that reduces the overhead of Translation Lookaside Buffer (TLB) lookups on machines with large amounts of memory by using larger memory pages.

However, database workloads often perform poorly with THP enabled, because they tend to have sparse rather than contiguous memory access patterns. When running MongoDB on Linux, THP should be disabled for best performance.

To ensure that THP is disabled before mongod starts, you should create a service file for your platform's initialization system that disables THP at boot. Instructions are provided below for both the systemd and the System V init initialization systems.

Additionally, for RHEL / CentOS systems that make use of ktune and tuned performance profiles, you must create a custom tuned profile as well.

Create a Service File

To create a service file that disables THP, you will use the built-in initialization system for your platform. Recent versions of Linux tend to use systemd (which uses the systemctl command), while older versions of Linux tend to use System V init (which uses the service command). Refer to the documentation for your operating system for more information.

Use the initialization system appropriate for your platform:

1

Create the systemd unit file

Create the following file and save it at /etc/systemd/system/disable-transparent-huge-pages.service:

[Unit]
Description=Disable Transparent Hugepages (THP)
DefaultDependencies=no
After=sysinit.target local-fs.target
Before=mongod.service
[Service]
Type=oneshot
ExecStart=/bin/sh -c 'echo never | tee /sys/kernel/mm/transparent_hugepage/enabled > /dev/null && echo never | tee /sys/kernel/mm/transparent_hugepage/defrag > /dev/null'
[Install]
WantedBy=basic.target

Note

Some versions of Red Hat Enterprise Linux, and potentially other Red Hat-based derivatives, use a different path for the THP enabled file:

/sys/kernel/mm/redhat_transparent_hugepage/enabled

Verify which path is in use on your system and update the disable-transparent-huge-pages.service file accordingly.

2

Reload systemd unit files

To reload the systemd unit files and make disable-transparent-huge-pages.service available for use, run the following command :

sudo systemctl daemon-reload
3

Start the service

Run:

sudo systemctl start disable-transparent-huge-pages

To verify that the relevant THP settings have changed, run the following command:

cat /sys/kernel/mm/transparent_hugepage/enabled && cat /sys/kernel/mm/transparent_hugepage/defrag

On Red Hat Enterprise Linux and potentially other Red Hat-based derivatives, you may instead need to use the following:

cat /sys/kernel/mm/redhat_transparent_hugepage/enabled && cat /sys/kernel/mm/redhat_transparent_hugepage/defrag

The output should resemble the following:

never
never
4

Configure your operating system to run it on boot

To ensure that this setting is applied each time the operating system starts, run the following command:

sudo systemctl enable disable-transparent-huge-pages
5

(Optional) Customize tuned or ktune profile

If you use tuned or ktune profiles on RHEL/ CentOS, you must also create a custom tuned profile.

1

Create the init.d script

Create the following file and save it at /etc/init.d/disable-transparent-hugepages:

#!/bin/bash
### BEGIN INIT INFO
# Provides:          disable-transparent-hugepages
# Required-Start:    $local_fs
# Required-Stop:
# X-Start-Before:    mongod mongodb-mms-automation-agent
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Short-Description: Disable Linux Transparent Hugepages
# Description:       Disable Linux Transparent Hugepages, to improve
#                    database performance.
### END INIT INFO
case $1 in
  start)
    if [ -d /sys/kernel/mm/transparent_hugepage ]; then
      thp_path=/sys/kernel/mm/transparent_hugepage
    elif [ -d /sys/kernel/mm/redhat_transparent_hugepage ]; then
      thp_path=/sys/kernel/mm/redhat_transparent_hugepage
    else
      return 0
    fi
    echo 'never' | tee /sys/kernel/mm/transparent_hugepage/enabled > /dev/null && echo 'never' | tee /sys/kernel/mm/transparent_hugepage/defrag > /dev/null
    unset thp_path
    ;;
esac
2

Make the script executable

Run:

sudo chmod 755 /etc/init.d/disable-transparent-hugepages
3

Run the script

Run:

sudo /etc/init.d/disable-transparent-hugepages start

To verify that the relevant THP settings have changed, run the following command:

cat /sys/kernel/mm/transparent_hugepage/enabled && cat /sys/kernel/mm/transparent_hugepage/defrag

On Red Hat Enterprise Linux and potentially other Red Hat-based derivatives, you may instead need to use the following:

cat /sys/kernel/mm/redhat_transparent_hugepage/enabled && cat /sys/kernel/mm/redhat_transparent_hugepage/defrag

The output should resemble the following:

never
never
4

Configure your operating system to run it on boot

To ensure that this setting is applied each time the operating sytem starts, run the following command for your Linux distribution:

Distribution
Command

Ubuntu and Debian

sudo update-rc.d disable-transparent-hugepages defaults

SUSE

sudo insserv /etc/init.d/disable-transparent-hugepages

Red Hat, CentOS, Amazon Linux, and derivatives

sudo chkconfig --add disable-transparent-hugepages
5

(Optional) Customize tuned or ktune profile

If you are using tuned or ktune profiles on RHEL/ CentOS, you must also create a custom tuned profile.

Using tuned and ktune

Important

If using tuned or ktune, you must also perform the steps in this section after creating the service file above.

tuned and ktune are dynamic kernel tuning tools that can affect the transparent huge pages setting on your system. If you are using tuned / ktune on your RHEL / CentOS system while running mongod, you must create a custom tuned profile to ensure that THP remains disabled.

Red Hat/CentOS 6

1

Create a new profile.

Create a new profile from an existing profile by copying the relevant directory. This example uses the virtual-guest profile as the base, and uses virtual-guest-no-thp as the new profile:

sudo cp -r /etc/tune-profiles/virtual-guest /etc/tune-profiles/virtual-guest-no-thp
2

Edit ktune.sh.

Edit /etc/tune-profiles/virtual-guest-no-thp/ktune.sh and change the set_transparent_hugepages setting to the following:

set_transparent_hugepages never
3

Enable the new profile.

Enable the new profile:

sudo tuned-adm profile virtual-guest-no-thp

Red Hat/CentOS 7 and 8

1

Create a new profile.

Create a new directory to hold the custom tuned profile. This example inherits from the existing virtual-guest profile, and uses virtual-guest-no-thp as the new profile:

sudo mkdir /etc/tuned/virtual-guest-no-thp
2

Edit tuned.conf.

Create and edit /etc/tuned/virtual-guest-no-thp/tuned.conf so that it contains the following:

[main]
include=virtual-guest
[vm]
transparent_hugepages=never

This example inherits from the existing virtual-guest profile. Select the profile most appropriate for your system.

3

Enable the new profile.

Enable the new profile:

sudo tuned-adm profile virtual-guest-no-thp

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