Transparent Huge Pages (THP) is a Linux memory management feature designed to reduce the overhead of translation lookaside buffer (page table) lookups on machines with large amounts of memory by using larger virtual memory pages. However, THP often causes performance problems for database workloads, because they tend to have sparse, rather than contiguous, memory access patterns. MongoDB, Inc. recommends disabling THP on servers running MongoDB.
Define a service unit to disable THP
Create a file on the master build server (casdev-master) called /etc/systemd/system/mongod-disable-thp.service with the following contents:
[Unit]
Description="Disable Transparent Huge Pages (THP) before mongod starts"
Before=mongod.service
[Service]
Type=oneshot
ExecStart=/bin/sh -c 'echo never > /sys/kernel/mm/transparent_hugepage/enabled'
ExecStart=/bin/sh -c 'echo never > /sys/kernel/mm/transparent_hugepage/defrag'
[Install]
RequiredBy=mongod.service
Install and enable the service unit
Run the commands
casdev-master# restorecon /etc/systemd/system/mongod-disable-thp.service
casdev-master# chmod 644 /etc/systemd/system/mongod-disable-thp.service
casdev-master# for i in 01 02 03
> do
> scp -p /etc/systemd/system/mongod-disable-thp.service casdev-srv${i}:/etc/systemd/system/mongod-disable-thp.service
> ssh casdev-srv${i} systemctl enable mongod-disable-thp
> done
mongod-disable-thp.service 100% 321 984.7KB/s 00:00
Created symlink from /etc/systemd/system/mongod.service.requires/mongod-disable-thp.service to /etc/systemd/system/mongod-disable-thp.service.
mongod-disable-thp.service 100% 321 1.0MB/s 00:00
Created symlink from /etc/systemd/system/mongod.service.requires/mongod-disable-thp.service to /etc/systemd/system/mongod-disable-thp.service.
mongod-disable-thp.service 100% 321 441.2KB/s 00:00
Created symlink from /etc/systemd/system/mongod.service.requires/mongod-disable-thp.service to /etc/systemd/system/mongod-disable-thp.service.
casdev-master#
to copy the service unit to the CAS servers and enable it to be executed by systemd. Do not enable the service unit on the master build server (casdev-master), since mongod will not be running there.