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: