hugepages: add some details on allocation

This commit add a little more details on pre-allocation
and dynamic allocation of huge pages on the node.

It also links to the Linux documentation for further
details but gives a quick example on multiple page sizes
that is not very obvious from the Linux documentation
currently.

Signed-off-by: Anthony Nandaa <[email protected]>

Author: profnandaa

content/en/docs/tasks/manage-hugepages/scheduling-hugepages.md

@@ -14,15 +14,43 @@ by applications in a Pod. This page describes how users can consume huge pages.
 
 ## {{% heading "prerequisites" %}}
 
+Kubernetes nodes must
+[pre-allocate huge pages](https://www.kernel.org/doc/html/latest/admin-guide/mm/hugetlbpage.html)
+in order for the node to report its huge page capacity.
 
-1. Kubernetes nodes must pre-allocate huge pages in order for the node to report
-   its huge page capacity. A node can pre-allocate huge pages for multiple
-   sizes.
+A node can pre-allocate huge pages for multiple sizes, for instance,
+the following line in `/etc/default/grub` allocates `2*1GiB` of 1 GiB
+and `512*2 MiB` of 2 MiB pages:
+
+```
+GRUB_CMDLINE_LINUX="hugepagesz=1G hugepages=2 hugepagesz=2M hugepages=512"
+```
 
 The nodes will automatically discover and report all huge page resources as
 schedulable resources.
 
+When you describe the node, you should see something similar to the following
+in the following in the `Capacity` and `Allocatable` sections:
+
+```
+Capacity:
+  cpu:                ...
+  ephemeral-storage:  ...
+  hugepages-1Gi:      2Gi
+  hugepages-2Mi:      1Gi
+  memory:             ...
+  pods:               ...
+Allocatable:
+  cpu:                ...
+  ephemeral-storage:  ...
+  hugepages-1Gi:      2Gi
+  hugepages-2Mi:      1Gi
+  memory:             ...
+  pods:               ...
+```
 
+> **NOTE:** For dynamically allocated pages (after boot), the Kubelet
+> needs to be restarted for the new allocations to be refrelected.
 
 <!-- steps -->