Disable Transparent Huge Pages (THP)
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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:
- systemd (systemctl)
- System V Init (service)
Create the systemd
unit file.
Create the following file at /etc/systemd/system/disable-transparent-huge-pages.service
:
Note
Some versions of Red Hat Enterprise Linux, and potentially other Red Hat-based derivatives, use a different path for the THP enabled
file:
Check to see which path is in use on your system, and update the disable-transparent-huge-pages.service
file accordingly.
Note
Prior to version 4.2, MongoDB also checks the THP defrag setting and presents a startup warning if defrag is enabled. As long as THP itself is disabled in the systemd
unit file, MongoDB is unaffected by the defrag setting. However, to avoid this message, you may set defrag to never
by adding the following additional line to the systemd
unit file, just after the existing ExecStart
statement:
If on Red Hat or similar, the path to the defrag
file might be different. See the note above for more details, and and update the disable-transparent-huge-pages.service
file accordingly.
Start the service.
Start the service manually once to ensure that the appropriate THP setting has been changed:
Verify that THP has successfully been set to [never]
by running the following command:
On Red Hat Enterprise Linux and potentially other Red Hat-based derivatives, you may instead need to use the following:
Create the init.d
script.
Create the following file at /etc/init.d/disable-transparent-hugepages
:
Note
MongoDB 3.6 also checks the THP defrag setting and presents a startup warning if defrag is enabled. As long as THP itself is disabled in the init.d
script, MongoDB is unaffected by the defrag setting. However, to avoid this message, you may set defrag to never
by adding the following line to the init.d
script, just before the unset thp_path
statement:
Run the script.
Run the script manually once to ensure that the appropriate THP setting has been changed:
Verify that THP has successfully been set to [never]
by running the following command:
On Red Hat Enterprise Linux and potentially other Red Hat-based derivatives, you may instead need to use the following:
Configure your operating system to run it on boot.
To ensure that this setting is applied each time your system boots, 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
|
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.