Monitoring the RSS of a Project

The following example shows project user1, which has an RSS in excess of its RSS cap.

The following command produces five reports at 5-second sampling intervals.

user1machine% rcapstat 5 5

    id project  nproc    vm   rss   cap    at avgat     pg  avgpg
376565   user1      3 6249M 6144M 6144M  690M  220M  5528K  2764K
376565   user1      3 6249M 6144M 6144M    0M  131M  4912K  1637K
376565   user1      3 6249M 6171M 6144M   27M  147M  6048K  2016K
376565   user1      3 6249M 6146M 6144M 4872M  174M  4368K  1456K
376565   user1      3 6249M 6156M 6144M   12M  161M  3376K  1125K

The user1 project has three processes that are actively using physical memory. The positive values in the pg column indicate that rcapd is consistently paging out memory as it attempts to meet the cap by lowering the physical memory utilization of the project's processes. However, rcapd does not succeed in keeping the RSS below the cap value. This is indicated by the varying rss values that do not show a corresponding decrease. As soon as memory is paged out, the workload uses it again and the RSS count goes back up. This means that all of the project's resident memory is being actively used and the working set size (WSS) is greater than the cap. Thus, rcapd is forced to page out some of the working set to meet the cap. Under this condition, the system will continue to experience high page fault rates, and associated I/O, until one of the following occurs:

• The WSS becomes smaller.

• The cap is raised.

• The application changes its memory access pattern.

In this situation, shortening the sample interval might reduce the discrepancy between the RSS value and the cap value by causing rcapd to sample the workload and enforce caps more frequently.

A page fault occurs when either a new page must be created or the system must copy in a page from a swap device.