42 Huge pages #

When a process uses RAM, the CPU marks it as used by that process. For efficiency, the CPU allocates RAM in chunks 4K bytes is the default value on many platforms. Those chunks are named pages. Pages can be swapped to disk, etc.

Since the process address space is virtual, the CPU and the operating system need to remember which pages belong to which process, and where each page is stored. The greater the number of pages, the longer the search for memory mapping. When a process uses 1 GB of memory, that is 262144 entries to look up (1 GB / 4 K). If a page table entry consumes 8 bytes, that is 2 MB (262144 * 8) to look up.

Most current CPU architectures support larger-than-default pages, which give the CPU/OS fewer entries to look up.

To enable the huge pages, we should add the following kernel parameters. In this example, we configure 40 1G pages, though the huge page size and exact number should be tailored to your application’s memory requirements:

Modify the GRUB file /etc/default/grub to add these parameters in GRUB_CMDLINE_LINUX:

default_hugepagesz=1G hugepagesz=1G hugepages=40 hugepagesz=2M hugepages=0

Update the GRUB configuration and reboot the system to apply the changes:

$ transactional-update grub.cfg
$ reboot

To validate that the parameters are applied after the reboot, you can check the command line:

$ cat /proc/cmdline

To use the huge pages, we need to mount them:

$ mkdir -p /hugepages
$ mount -t hugetlbfs nodev /hugepages

Deploy a Kubernetes workload, creating the resources and the volumes:

...
 resources:
   requests:
     memory: "24Gi"
     hugepages-1Gi: 16Gi
     intel.com/intel_sriov_oru: '4'
   limits:
     memory: "24Gi"
     hugepages-1Gi: 16Gi
     intel.com/intel_sriov_oru: '4'
...

...
volumeMounts:
  - name: hugepage
    mountPath: /hugepages
...
volumes:
  - name: hugepage
    emptyDir:
      medium: HugePages
...