Bug 1845198

Summary:	[Doc] Need documentation around usage of huge-pages
Product:	Container Native Virtualization (CNV)	Reporter:	Kedar Bidarkar <kbidarka>
Component:	Documentation	Assignee:	Andrew Burden <aburden>
Status:	CLOSED CURRENTRELEASE	QA Contact:	Nelly Credi <ncredi>
Severity:	high	Docs Contact:
Priority:	high
Version:	2.4.0	CC:	aburden, cnv-qe-bugs, rmohr
Target Milestone:	---
Target Release:	2.4.0
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:
Fixed In Version:	2.4.0	Doc Type:	If docs needed, set a value
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2020-07-31 13:33:20 UTC	Type:	Bug
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description Kedar Bidarkar 2020-06-08 15:55:21 UTC

Document URL: 

CNV-2.3/OCP4.4 

Section Number and Name: 

Describe the issue: 

Use could end up with incorrect hugepages configuration and we would like to have a documentation for this feature.

A bug was raised, with unexpected behaviour. https://bugzilla.redhat.com/show_bug.cgi?id=1822875


Suggestions for improvement: 
We, would want to have documentation, to address the hugepages expected behavior here.

Additional information:

Comment 1 Kedar Bidarkar 2020-06-08 15:55:55 UTC

User could end up with incorrect hugepages configuration and we would like to have a documentation for this feature.

Comment 2 Kedar Bidarkar 2020-06-08 16:01:26 UTC

Current upstream documentation around hugepages is, https://kubevirt.io/2018/Kubevirt-v0.7.0.html 

From the bug, https://bugzilla.redhat.com/show_bug.cgi?id=1822875#c14  

Was expecting, "HugePages_Total:       2", 
but we got     "HugePages_Total:       1"

Memory/RAM was specified as 4Gi in VM spec file and 
we see it as approx 4Gi (3.7G) as seen from above "free -h", in comment 12.

Comment 4 Andrew Burden 2020-07-03 11:08:47 UTC

@Nelly, yes. OpenShift docs cover the node side for pre-allocating hugepages:
https://docs.openshift.com/container-platform/4.4/scalability_and_performance/what-huge-pages-do-and-how-they-are-consumed-by-apps.html#configuring-huge-pages_huge-pages

The work for this then is defining it in the VM config, and the the upstream doc for that looks good. 
We can do this for 2.4. I've updated the flag.

Comment 5 Andrew Burden 2020-07-13 14:04:58 UTC

Moving to ON_QA but adding need_info on Kedar for attention in case he would like to review. 

I have drafted some content to cover configuring VM to use huge pages:

PR: https://github.com/openshift/openshift-docs/pull/23705/files
Build: https://cnv-bz1845198-hugepages--ocpdocs.netlify.app/openshift-enterprise/latest/virt/virtual_machines/advanced_vm_management/virt-using-huge-pages-with-vms.html

Please note, the 'What huge pages do' module is reused from OpenShift docs - I've just conditionalises the final line so that it referes to VMs instead of Pods.

Comment 7 Andrew Burden 2020-07-21 18:22:24 UTC

The hugepages docs PR was merged:
https://github.com/openshift/openshift-docs/pull/23705

I will add a link to the docs when they are published for 2.4

Comment 8 Andrew Burden 2020-07-31 13:33:20 UTC

This was published with the OpenShift Virtualization 2.4 release.

You can view the content here:
https://docs.openshift.com/container-platform/4.5/virt/virtual_machines/advanced_vm_management/virt-using-huge-pages-with-vms.html