Bug 1148419

Summary:	The description of vm.swappiness need to be updated
Product:	Red Hat Enterprise Linux 7	Reporter:	Jerome Marchand <jmarchan>
Component:	doc-Performance_Tuning_Guide	Assignee:	Charlie <cboyle>
Status:	CLOSED NEXTRELEASE	QA Contact:	ecs-bugs
Severity:	unspecified	Docs Contact:
Priority:	medium
Version:	7.0	CC:	cboyle, ecs-bugs, rlandman
Target Milestone:	rc	Keywords:	Documentation
Target Release:	---
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:
Fixed In Version:		Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:	1148414	Environment:
Last Closed:	2015-04-07 23:47:34 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:
Bug Depends On:	1148414
Bug Blocks:

Description Jerome Marchand 2014-10-01 12:30:04 UTC

+++ This bug was initially created as a clone of Bug #1148414 +++

Document URL: 
http://documentation-devel.engineering.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html-single/Performance_Tuning_Guide/index.html

Section Number and Name: 
5.5. Tuning Virtual Memory

Describe the issue: 
The current description of vm.swappiness have two shortcomings:
 - it doesn't explain what swappiness really do: tune the trade-off between page cache and anonymous page. 
 - since rhel 6.4, swappiness==0 is more aggressive in avoiding swapping out. When the I/O activity is high, it increase risk of OOM killing.

Suggestions for improvement:

Current description:
    A value from 0 to 100 which controls the degree to which the system swaps. A high value prioritizes system performance, aggressively swapping processes out of physical memory when they are not active. A low value prioritizes interactivity and avoids swapping processes out of physical memory for as long as possible, which decreases response latency. The default value is 60. 

Proposed description:
    A value from 0 to 100 which controls the degree to which the system favour anonymous memory or the page cache. A high value improves file-system performance, while aggressively swapping less active processes out of RAM. 
A low value avoids swapping processes out of memory, which usually decrease latency, at the cost of I/O performance. The default value is 60.
Warning: Since RHEL 6.4, setting swappiness==0 will even more aggressively avoids swapping out, which increase the risk of OOM killing under strong memory and I/O pressure.


Additional information:

Comment 1 Jerome Marchand 2014-10-01 12:32:46 UTC

On RHEL 7, there is no need to mention the change that occurs in RHEL 6.4.

Proposed description:
    A value from 0 to 100 which controls the degree to which the system favour anonymous memory or the page cache. A high value improves file-system performance, while aggressively swapping less active processes out of RAM. 
A low value avoids swapping processes out of memory, which usually decrease latency, at the cost of I/O performance. The default value is 60.
Warning: Setting swappiness==0 will very aggressively avoids swapping out, which increase the risk of OOM killing under strong memory and I/O pressure.

Comment 3 Laura Bailey 2014-10-13 00:21:58 UTC

Thanks Jerome; marking this docs-async, as fixing it does not need to coincide with a specific release date.

Comment 4 Charlie 2015-04-07 23:47:34 UTC

Thanks Jerome, the text and warning has been included in the manual for the next release. 

http://documentation-devel.engineering.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Performance_Tuning_Guide/sect-Red_Hat_Enterprise_Linux-Performance_Tuning_Guide-Memory-Configuration_tools.html#sect-Red_Hat_Enterprise_Linux-Performance_Tuning_Guide-Configuration_tools-Configuring_system_memory_capacity