Configure Huge Pages

In Clear Linux OS hugepages are enabled by default. The default hugepage size is 2MB. The total number of hugepages is set to 0 by default. This guide shows you how to add hugepages to the system and how to change the default hugepage size.

1. To check the enabled state, run the following command.

   cat /sys/kernel/mm/transparent_hugepage/enabled
   

   The output will look like

   [always] madvise never
   

   Note

   The active option is enclosed in brackets. In this case, always is active, which means hugepages are enabled for every process. The madvise option means that hugepages are enabled for processes that explicitly call madvise.

2. To check the size of hugepages, run the below command.

   cat /proc/meminfo | grep Huge
   

   The output should look similar to the following. Although hugepages is enabled, there are no hugepages available to allocate.

   AnonHugePages:    624640 kB
   ShmemHugePages:        0 kB
   FileHugePages:         0 kB
   HugePages_Total:       0
   HugePages_Free:        0
   HugePages_Rsvd:        0
   HugePages_Surp:        0
   Hugepagesize:       2048 kB
   Hugetlb:               0 kB
   

3. If you need 1GB (1,048,576 bytes) of hugepages enabled, then HugePages_Total should be set to 512. Enable it temporarily using the following.

   echo 512 | sudo tee /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
   

   To view the change, run the command in the previous setp again.

4. Changing hugepages from the default 2MB to 1GB must be done at system boot through kernel boot parameters. In this example, we configure the size and number of allocatable huge pages at boot.

   sudo mkdir -p /etc/kernel/cmdline.d
   cat << EOF | sudo tee -a /etc/kernel/cmdline.d/hugepages.conf
   default_hugepagesz=1G
   hugepagesz=1G
   hugepages=10
   EOF
   sudo clr-boot-manager update
   sudo reboot