11.6. Managing transparent huge pages

Procedure

1. Check the status of THP:

   $ cat /sys/kernel/mm/transparent_hugepage/enabled

2. Configure THP.

   • Enabling THP:

     $ echo always > /sys/kernel/mm/transparent_hugepage/enabled

   • Disabling THP:

     $ echo never > /sys/kernel/mm/transparent_hugepage/enabled

   • Setting THP to madvise:

     $ echo madvise > /sys/kernel/mm/transparent_hugepage/enabled

     To prevent applications from allocating more memory resources than necessary, disable the system-wide transparent huge pages and only enable them for the applications that explicitly request it through the madvise system call.

     注意

     Sometimes, providing low latency to short-lived allocations has higher priority than immediately achieving the best performance with long-lived allocations. In such cases, you can disable direct compaction while leaving THP enabled.

     Direct compaction is a synchronous memory compaction during the huge page allocation. Disabling direct compaction provides no guarantee of saving memory, but can decrease the risk of higher latencies during frequent page faults. Also, disabling direct compaction allows synchronous compaction of Virtual Memory Areas (VMAs) highlighted in madvise only. Note that if the workload benefits significantly from THP, the performance decreases. Disable direct compaction:

     $ echo never > /sys/kernel/mm/transparent_hugepage/defrag

     See the madvise(2) man page on your system for more information.

Procedure

1. Copy the active profile file to the same directory:

   $ sudo cp -R /usr/lib/tuned/my_profile /usr/lib/tuned/my_copied_profile

2. Edit the tune.conf file:

   $ sudo vi /usr/lib/tuned/my_copied_profile/tuned.conf

   • To enable THP, add the line:

     [bootloader]
     
     cmdline = transparent_hugepage=always

   • To disable THP, add the line:

     [bootloader]
     
     cmdline = transparent_hugepage=never

   • To set THP to madvise, add the line:

     [bootloader]
     
     cmdline = transparent_hugepage=madvise

3. Restart the TuneD service:

   $ sudo systemctl restart tuned

4. Set the new profile active:

   $ sudo tuned-adm profile my_copied_profile

Verification

1. Verify that the new profile is active:

   $ sudo tuned-adm active

2. Verify that the required mode of THP is set:

   $ cat /sys/kernel/mm/transparent_hugepage/enabled

Procedure

1. Get the current kernel command line parameters:

   # grubby --info=$(grubby --default-kernel)
   kernel="/boot/vmlinuz-6.12.X-XXX.XX.X.el10_0.x86_64"
   args="ro crashkernel=1G-4G:192M,4G-64G:256M,64G-:512M resume=UUID=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXXX console=tty0 console=ttyS0"
   root="UUID=XXXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX"
   initrd="/boot/initramfs-6.12.X-XXX.XX.X.el10_0.x86_64.img"
   title="Red Hat Enterprise Linux (6.12.X-XXX.XX.X.el10_0.x86_64) 10.0"
   id="XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX-6.12.X-XXX.XX.X.el10_0.x86_64"

2. Configure THP by adding kernel parameters.

   • To enable THP:

     # grubby --args="transparent_hugepage=always" --update-kernel=DEFAULT

   • To disable THP:

     # grubby --args="transparent_hugepage=never" --update-kernel=DEFAULT

   • To set THP to madvise:

     # grubby --args="transparent_hugepage=madvise" --update-kernel=DEFAULT

3. Reboot the system for changes to take effect:

   # reboot

Procedure

1. Create new systemd service files for enabling, disabling and setting THP to madvise. For example, /etc/systemd/system/disable-thp.service.

2. Configure THP by adding the following contents to a new systemd service file.

   • To enable THP, add the following content to <new_thp_file>.service file:

     [Unit]
     Description=Enable Transparent Hugepages
     After=local-fs.target
     Before=sysinit.target
     
     [Service]
     Type=oneshot
     RemainAfterExit=yes
     ExecStart=/bin/sh -c 'echo always > /sys/kernel/mm/transparent_hugepage/enabled
     
     [Install]
     WantedBy=multi-user.target

   • To disable THP, add the following content to <new_thp_file>.service file:

     [Unit]
     Description=Disable Transparent Hugepages
     After=local-fs.target
     Before=sysinit.target
     
     [Service]
     Type=oneshot
     RemainAfterExit=yes
     ExecStart=/bin/sh -c 'echo never > /sys/kernel/mm/transparent_hugepage/enabled
     
     [Install]
     WantedBy=multi-user.target

   • To set THP to madvise, add the following content to <new_thp_file>.service file:

     [Unit]
     Description=Madvise Transparent Hugepages
     After=local-fs.target
     Before=sysinit.target
     
     [Service]
     Type=oneshot
     RemainAfterExit=yes
     ExecStart=/bin/sh -c 'echo madvise > /sys/kernel/mm/transparent_hugepage/enabled
     
     [Install]
     WantedBy=multi-user.target

3. Enable and start the service:

   # systemctl enable <new_thp_file>.service

   # systemctl start <new_thp_file>.service