How do I view the number of 1GB hugetables (and what documentation should I follow)?

Question

I am trying to figure out hugepages for use by KVM under Ubuntu 20.04. If I change the number of 2048 KiB (the default size) pages, I see that is reflected in /proc/meminfo

:~$ echo 0 |sudo tee /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
0
:~$ cat /proc/meminfo | grep Huge
AnonHugePages:         0 kB
ShmemHugePages:        0 kB
FileHugePages:         0 kB
HugePages_Total:       0
HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
Hugetlb:        50331648 kB
:~$ echo 512 |sudo tee /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
512
:~$ cat /proc/meminfo | grep Huge
AnonHugePages:         0 kB
ShmemHugePages:        0 kB
FileHugePages:         0 kB
HugePages_Total:     512
HugePages_Free:      512
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
Hugetlb:        51380224 kB
:~$ 

However, when I change the number of 1GB pages, I don't see anything to reflect that.

:~$ echo 0 | sudo tee /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages
0
:~$ cat /proc/meminfo | grep Huge
AnonHugePages:         0 kB
ShmemHugePages:        0 kB
FileHugePages:         0 kB
HugePages_Total:     512
HugePages_Free:      512
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
Hugetlb:        51380224 kB
:~$ echo 16 | sudo tee /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages
16
:~$ cat /proc/meminfo | grep Huge
AnonHugePages:         0 kB
ShmemHugePages:        0 kB
FileHugePages:         0 kB
HugePages_Total:     512
HugePages_Free:      512
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
Hugetlb:        51380224 kB

And as I understand it, this means that 1GB hugepages are supported by my system, right?

ls /sys/kernel/mm/hugepages
hugepages-1048576kB  hugepages-2048kB

Are 1Gb pages listed somewhere else? Can I check on their status?

Edit: I can see my 1GB hugepages thanks to @Krackout, but I am still confused about what documentation I should even be following:

I am confused about varying procedures for setting up and monitoring hugepages. I seem to have got them working, but there is still quite a bit that is not clear to me.

Main resources:

• https://help.ubuntu.com/community/KVM%20-%20Using%20Hugepages
• https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/virtualization_tuning_and_optimization_guide/sect-virtualization_tuning_optimization_guide-memory-tuning
• https://mathiashueber.com/configuring-hugepages-use-virtual-machine/
• https://wiki.archlinux.org/index.php/KVM
• https://wiki.debian.org/Hugepages

Each of the above links describes partially overlapping procedures. It seems that differences based on kernel and distro, but it isn't clear to me what exactly they are and I can't seem to find it explcitly spelled out anywhere.

On my Ubuntu 20.04 setup, what works for me is putting the following in crontab -e:

@reboot echo 64 | sudo tee /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages
@reboot mount -t hugetlbfs -o pagesize=1G none /dev/hugepages

After which I can start a KVM VM in virt-manager containing the following XML:

<memoryBacking>
  <hugepages>
    <page size='1048576' unit='KiB'/>
  </hugepages>
</memoryBacking>

So the way I was able to do isn't exactly what any of the guides said.

Answer 1

In Debian Linux a kernel parameter needs to be inserted, hugepagesz=1G (and reboot of course). You can also install libhugetlbfs-bin package and view info using hugeadm command. The Debian wiki page on hugepades should apply to Ubuntu, which is Debian-based.

Answer 2

1. Run virsh capabilities on your host, it will show the enabled hugepages on this host:

   # virsh capabilities
       <topology>
             <cells num='2'>
               <cell id='0'>
                 <memory unit='KiB'>16088120</memory>
                 <pages unit='KiB' size='4'>3382030</pages>
                 <pages unit='KiB' size='2048'>1250</pages>
                 <pages unit='KiB' size='1048576'>0</pages>
                 ----to be continued-----
        <cell id='1'>
                 <memory unit='KiB'>16466052</memory>
                 <pages unit='KiB' size='4'>2427937</pages>
                 <pages unit='KiB' size='2048'>1250</pages>
                 <pages unit='KiB' size='1048576'>4</pages>
                 <distances> 
   

2. Check the system file for the usage and current status for each node:

   # cat /sys/devices/system/node/node0/hugepages/hugepages-1048576kB/free_hugepages
   0
   # cat /sys/devices/system/node/node0/hugepages/hugepages-1048576kB/nr_hugepages
   0
   # cat /sys/devices/system/node/node1/hugepages/hugepages-1048576kB/nr_hugepages
   4
   # cat /sys/devices/system/node/node1/hugepages/hugepages-1048576kB/free_hugepages
   3
   

   (node 0 has no 1G hugepage page; node 1 have 4 1G hugepage, 3 are free)