Bug 1148414

Summary: The description of vm.swappiness need to be updated
Product: Red Hat Enterprise Linux 6 Reporter: Jerome Marchand <jmarchan>
Component: doc-Performance_Tuning_GuideAssignee: Russell Dickenson <rdickens>
Status: CLOSED CURRENTRELEASE QA Contact: ecs-bugs
Severity: unspecified Docs Contact:
Priority: high    
Version: 6.5CC: dayleparker, jmarchan, jsnitsel, mnavrati
Target Milestone: rcKeywords: Documentation
Target Release: ---   
Hardware: Unspecified   
OS: Unspecified   
Fixed In Version: Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of:
: 1148419 1187221 (view as bug list) Environment:
Last Closed: 2016-05-24 15:59:48 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---
Bug Depends On:    
Bug Blocks: 1148419    

Description Jerome Marchand 2014-10-01 12:26:07 UTC
Document URL: 

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 2 Laura Bailey 2014-10-27 00:32:53 UTC
Adding docs-async to Devel Whiteboard, since this can be corrected asynchronous to the release schedule.

Comment 3 Jerry Snitselaar 2014-11-11 17:29:49 UTC
Hello Laura,

Any idea on what the turn around for this would be?


Comment 14 Milan Navratil 2016-05-24 15:59:48 UTC
Latest version of the Red Hat Enterprise Linux 6 Performance Tuning Guide on the Red Hat Customer Portal:


Closing this BZ.