Bug 1376289

Summary:	[Docs] All hosts filtered out when memory underutilized parameter left out
Product:	Red Hat Enterprise Virtualization Manager	Reporter:	Tahlia Richardson <trichard>
Component:	Documentation	Assignee:	rhev-docs <rhev-docs>
Status:	CLOSED DUPLICATE	QA Contact:	rhev-docs <rhev-docs>
Severity:	unspecified	Docs Contact:
Priority:	unspecified
Version:	4.0.0	CC:	gklein, lbopf, lsurette, melewis, rbalakri, srevivo, trichard, ykaul, ylavi
Target Milestone:	ovirt-4.0.7
Target Release:	---
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:
Fixed In Version:		Doc Type:	If docs needed, set a value
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2017-02-01 03:04:18 UTC	Type:	Bug
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	Docs	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	1354281, 1359767
Bug Blocks:

Description Tahlia Richardson 2016-09-15 04:23:07 UTC

The doc text from the following bug has a documentation request:  https://bugzilla.redhat.com/show_bug.cgi?id=1354281

"Cause:
Setting only one of the thresholds for power saving/evenly distributed memory based balancing (high or low) might lead to unexpected results.

Specific to this bug-
In power saving load balancing the threshold for memory over utilized hosts is set with a value and the threshold for memory under utilized host is undefined thus getting a default value of 0.

Consequence:
All hosts are considered as under utilized hosts and are chosen as sources for migration.
No host is chosen as a destination for migration.

Fix:
1.Documentation fix is needed, add the following limitation:

"Setting only one of the thresholds in memory based balancing (high or low) might lead to unexpected results."

2.When the threshold for memory under utilized host is undefined - it gets a default value of Long.MAX

Result:
1.After the documentation fix users will be guided not to choose only one of the memory thresholds for power saving / evenly distributed load balancing (preventing unwanted behaviour)

2.When in power saving load balancing the threshold for memory over utilized hosts is set with a value and the threshold for memory under utilized host is undefined:
- only over utilized hosts will be selected as sources for migration.
- destination hosts will be hosts that are not over utilized"


Comments in the bug are also quite detailed. 

Should just require adding a note to https://access.redhat.com/documentation/en/red-hat-virtualization/4.0/single/administration-guide/#Configuring_scheduling_policy and maybe the settings table.

Comment 1 Megan Lewis 2016-09-21 00:54:47 UTC

A 3.6 doc text bug also requests the same changes: 
https://bugzilla.redhat.com/show_bug.cgi?id=1359767

This bug is a clone of the bug mentioned above. 

"Cause: 
Setting only one of the thresholds for power saving/evenly distributed memory based balancing (high or low) might lead to unexpected results.

Specific to this bug- 
In power saving load balancing the threshold for memory over utilized hosts is set with a value and the threshold for memory under utilized host is undefined thus getting a default value of 0. 

Consequence: 
All hosts are considered as under utilized hosts and are chosen as sources for migration.
No host is chosen as a destination for migration.

Fix:
1.Documentation fix is needed, add the following limitation:

"Setting only one of the thresholds in memory based balancing (high or low) might lead to unexpected results."

2.When the threshold for memory under utilized host is   undefined - it gets a default value of Long.MAX

Result: 
1.After the documentation fix users will be guided not to choose only one of the memory thresholds for power saving / evenly distributed load balancing (preventing unwanted behaviour)

2.When in power saving load balancing the threshold for memory over utilized hosts is set with a value and the threshold for memory under utilized host is undefined:
- only over utilized hosts will be selected as sources for migration.
- destination hosts will be hosts that are not over utilized"

Comment 2 Lucy Bopf 2017-01-31 08:40:10 UTC

Tahlia, I think the same change is requested in bug 1360696. Can you confirm, and close this one as a duplicate if bug 1360696 covers the same change?

Comment 3 Tahlia Richardson 2017-02-01 03:04:18 UTC

Yes, I think this is same, or at least a similar, request. They both reference the same engineering bug. I'll include the doc text from this bug description as a comment in the other bug, and close this one as a duplicate.

*** This bug has been marked as a duplicate of bug 1360696 ***