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- Disable Transparent Huge Pages (THP)
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, because they tend to have sparse rather than contiguous memory access patterns. You should disable THP on Linux machines to ensure best performance with MongoDB.
Init Script¶
Important
If you are using tuned or ktune (for example, if you are running Red Hat or CentOS 6+), you must additionally configure them so that THP is not re-enabled. See Using tuned and ktune.
Create the init.d script.¶
Create the following file at /etc/init.d/disable-transparent-hugepages:
#!/bin/sh
### 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 huge pages
# Description: Disable Linux transparent huge pages, 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' > ${thp_path}/enabled
echo 'never' > ${thp_path}/defrag
unset thp_path
;;
esac
Make it executable.¶
Run the following command to ensure that the init script can be used:
sudo chmod 755 /etc/init.d/disable-transparent-hugepages
Configure your operating system to run it on boot.¶
Use the appropriate command to configure the new init script on 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
|
Override tuned and ktune, if applicable¶
If you are using tuned or ktune (for example, if you are running Red Hat or CentOS 6+) you must now configure them to preserve the above settings.
Using tuned and ktune¶
Important
If using tuned or ktune, you must perform this step in addition to installing the init script.
tuned and ktune are dynamic kernel tuning tools available on Red Hat and CentOS that can disable transparent huge pages.
To disable transparent huge pages in tuned or ktune, you need to edit or create a new profile that sets THP to never.
Red Hat/CentOS 6¶
Create a new profile.¶
Create a new profile from an existing default profile by copying the relevant directory. In the example we use the default profile as the base and call our new profile no-thp.
sudo cp -r /etc/tune-profiles/default /etc/tune-profiles/no-thp
Edit ktune.sh.¶
Edit /etc/tune-profiles/no-thp/ktune.sh and add the following:
set_transparent_hugepages never
to the start() block of the file, before the return 0 statement.
Test Your Changes¶
You can check the status of THP support by issuing the following commands:
cat /sys/kernel/mm/transparent_hugepage/enabled
cat /sys/kernel/mm/transparent_hugepage/defrag
On Red Hat Enterprise Linux, CentOS, 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
For both files, the correct output resembles:
always madvise [never]
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