Determining the Working Set Size of a Project

The following example is a continuation of the previous example, and it uses the same project.

The previous example shows that the user1 project is using more physical memory than its cap allows. This example shows how much memory the project workload requires.

user1machine% rcapstat 5 5
    id project  nproc    vm   rss   cap    at avgat     pg  avgpg
376565   user1      3 6249M 6144M 6144M  690M    0K   689M     0K
376565   user1      3 6249M 6144M 6144M    0K    0K     0K     0K
376565   user1      3 6249M 6171M 6144M   27M    0K    27M     0K
376565   user1      3 6249M 6146M 6144M 4872K    0K  4816K     0K
376565   user1      3 6249M 6156M 6144M   12M    0K    12M     0K
376565   user1      3 6249M 6150M 6144M 5848K    0K  5816K     0K
376565   user1      3 6249M 6155M 6144M   11M    0K    11M     0K
376565   user1      3 6249M 6150M   10G   32K    0K    32K     0K
376565   user1      3 6249M 6214M   10G    0K    0K     0K     0K
376565   user1      3 6249M 6247M   10G    0K    0K     0K     0K
376565   user1      3 6249M 6247M   10G    0K    0K     0K     0K
376565   user1      3 6249M 6247M   10G    0K    0K     0K     0K
376565   user1      3 6249M 6247M   10G    0K    0K     0K     0K
376565   user1      3 6249M 6247M   10G    0K    0K     0K     0K
376565   user1      3 6249M 6247M   10G    0K    0K     0K     0K

Halfway through the cycle, the cap on the user1 project was increased from 6 gigabytes to 10 gigabytes. This increase stops cap enforcement and allows the resident set size to grow, limited only by other processes and the amount of memory in the machine. The rss column might stabilize to reflect the project working set size (WSS), 6247M in this example. This is the minimum cap value that allows the project's processes to operate without continuously incurring page faults.

While the cap on user1 is 6 gigabytes, in every 5–second sample interval the RSS decreases and I/O increases as rcapd pages out some of the workload's memory. Shortly after a page out completes, the workload, needing those pages, pages them back in as it continues running. This cycle repeats until the cap is raised to 10 gigabytes, approximately halfway through the example. The RSS then stabilizes at 6.1 gigabytes. Since the workload's RSS is now below the cap, no more paging occurs. The I/O associated with paging stops as well. Thus, the project required 6.1 gigabytes to perform the work it was doing at the time it was being observed.

Also see the vmstat(1M) and iostat(1M) man pages.