7.3. Configuring HugeTLB Huge Pages

Procedure 7.1. Reserving 1 GB Pages During Early Boot

1. Create a HugeTLB pool for 1 GB pages by appending the following line to the kernel command-line options in the /etc/default/grub file as root:

   default_hugepagesz=1G hugepagesz=1G
   

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2. Regenerate the GRUB2 configuration using the edited default file. If your system uses BIOS firmware, execute the following command:

   # grub2-mkconfig -o /boot/grub2/grub.cfg
   

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   On a system with UEFI firmware, execute the following command:

     # grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg
   

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3. Create a file named /usr/lib/systemd/system/hugetlb-gigantic-pages.service with the following content:

   [Unit]
   Description=HugeTLB Gigantic Pages Reservation
   DefaultDependencies=no
   Before=dev-hugepages.mount
   ConditionPathExists=/sys/devices/system/node
   ConditionKernelCommandLine=hugepagesz=1G
   
   [Service]
   Type=oneshot
   RemainAfterExit=yes
   ExecStart=/usr/lib/systemd/hugetlb-reserve-pages.sh
   
   [Install]
   WantedBy=sysinit.target
   

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4. Create a file named /usr/lib/systemd/hugetlb-reserve-pages.sh with the following content:

   #!/bin/sh
   
   nodes_path=/sys/devices/system/node/
   if [ ! -d $nodes_path ]; then
   	echo "ERROR: $nodes_path does not exist"
   	exit 1
   fi
   
   reserve_pages()
   {
   	echo $1 > $nodes_path/$2/hugepages/hugepages-1048576kB/nr_hugepages
   }
   
   reserve_pages number_of_pages node

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   On the last line, replace number_of_pages with the number of 1GB pages to reserve and node with the name of the node on which to reserve these pages.

   Example 7.1. Reserving Pages on node0 and node1

   For example, to reserve two 1GB pages on node0 and one 1GB page on node1, replace the last line with the following code:

   reserve_pages 2 node0
   reserve_pages 1 node1
   

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   You can modify it to your needs or add more lines to reserve memory in other nodes.
5. Make the script executable:

   # chmod +x /usr/lib/systemd/hugetlb-reserve-pages.sh
   

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6. Enable early boot reservation:

   # systemctl enable hugetlb-gigantic-pages
   

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