How to avoid transparent_hugepage/defrag warning from mongodb?
LinuxMongodbLinux KernelLinux Problem Overview
I'm receiving the following warning from mongodb about THP
2015-03-06T21:01:15.526-0800 I CONTROL [initandlisten] ** WARNING: /sys/kernel/mm/transparent_hugepage/defrag is 'always'.
2015-03-06T21:01:15.526-0800 I CONTROL [initandlisten] ** We suggest setting it to 'never'
But I did manage to turned THP off manually
frederick@UbuntuVirtual:~$ cat /sys/kernel/mm/transparent_hugepage/enabled
always madvise [never]
frederick@UbuntuVirtual:~$ cat /sys/kernel/mm/transparent_hugepage/defrag
always madvise [never]
I did the trick by adding transparent_hugepage=never
to GRUB_CMDLINE_LINUX_DEFAULT
in /etc/default/grub
and adding
if test -f /sys/kernel/mm/transparent_hugepage/defrag; then
echo never > /sys/kernel/mm/transparent_hugepage/defrag
fi
to /etc/rc.local
How on earth can I avoid the warning?
Linux Solutions
Solution 1 - Linux
Official MongoDB documentation gives several solutions for this issue. You can also try this solution, which worked for me:
Note: Try official documentation directives if MongoDB version is greater than 3.0
-
Open
/etc/init.d/mongod
file.
(if no such file you might check/etc/init.d/mongod
,/etc/init/mongod.conf
files - credit: the below comments) -
Add the lines below immediately after
chown $DAEMONUSER /var/run/mongodb.pid
and beforeend script
. -
Restart
mongod
(service mongod restart
).
Here are the lines to add to /etc/init.d/mongod
:
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
That's it!
Solution 2 - Linux
MongoDB have updated their recommendation to use an init.d script now: http://docs.mongodb.org/master/tutorial/transparent-huge-pages/
Solution 3 - Linux
For Ubuntu 14.04 using upstart:
Since we are deploying machines with Ansible I don't like modifying rc files or GRUB configs.
I tried using sysfsutils
/ sysfs.conf
but ran into timing issues when starting the services on fast (or slow machines). It looked like sometimes mongod was started before sysfsutils. Sometimes it worked, sometimes it did not.
Since mongod is an upstart process I found that the cleanest solution was to add the file /etc/init/mongod_vm_settings.conf
with the following content:
# Ubuntu upstart file at /etc/init/mongod_vm_settings.conf
#
# This file will set the correct kernel VM settings for MongoDB
# This file is maintained in Ansible
start on (starting mongod)
script
echo "never" > /sys/kernel/mm/transparent_hugepage/enabled
echo "never" > /sys/kernel/mm/transparent_hugepage/defrag
end script
This will run the script just before mongod will be started.
Restart mongod (sudo service mongod restart
) and done.
Solution 4 - Linux
-
Open /etc/default/grub
sudo vi /etc/default/grub
-
Update
GRUB_CMDLINE_LINUX_DEFAULT="" to GRUB_CMDLINE_LINUX_DEFAULT="transparent_hugepage=never" -
Save file
:wq (in vi) -
Run update-grub
sudo update-grub
-
Reboot machine
Update: If you are using a virtual hosting provider, this will work IFF grub boot is supported. DigitalOcean DOES NOT support grub boot.
Solution 5 - Linux
Verified that the defrag is examined without regard to the enabled:
$ cat /sys/kernel/mm/transparent_hugepage/enabled
always madvise [never]
$ cat /sys/kernel/mm/transparent_hugepage/defrag
[always] madvise never
$ service mongod start
... (in log) WARNING: /sys/kernel/mm/transparent_hugepage/defrag is 'always'
$ echo 'never' > /sys/kernel/mm/transparent_hugepage/defrag
$ cat /sys/kernel/mm/transparent_hugepage/defrag
always madvise [never]
$ service mongod stop
$ service mongod start
... (no warning in log)
Therefore, the fix to this bug is to first look at transparent_hugepage/enabled, and if it is never, don't bother looking at the irrelevant transparent_hugepage/defrag setting.
Solution 6 - Linux
Ubuntu 16.04 using systemd:
systemctl edit mongod
Paste the following:
[Service]
PermissionsStartOnly=true
ExecStartPre=/bin/sh -c "echo never > /sys/kernel/mm/transparent_hugepage/enabled"
ExecStartPre=/bin/sh -c "echo never > /sys/kernel/mm/transparent_hugepage/defrag"