Capping a Solaris processes memory

Solaris 10 introduced numerous capabilities, including the ability to use memory caps to limit the amount of memory available to a project. Memory caps are configured through the project(4) facility, and use the rcap.max-rss resource control to limit the amount of memory that a project can consume. Memory caps are enforced by the rcapd daemon, which is a userland process that periodically checks process memory usage, and takes action when a process has exceeded it’s alloted amount of memory. To use memory caps on a server or inside a zone, the rcapadm utility needs to be run with the “-E” (enable memory caps) option to enable memory caps:

$ rcapadm -E

In addition to starting rcapd, the capadm utility will enable the SMF services to start rcapd when the system boots. To see if memory caps are enabled on a system, the rcapadm utility can be run without any arguments:

$ rcapadm

                                 state: enabled
      memory cap enforcement threshold: 0%
               process scan rate (sec): 15
            reconfiguration rate (sec): 60
                     report rate (sec): 5
               RSS sampling rate (sec): 5

After memory capping is enabled, the projmod utility can be used to configure memory caps. To configure a 512MB memory cap for all processes that run as the user apache, the projmod utility can be run with the “-K” option, and the rcap.max-rss resource control set to the amount of memory you would like to assign to the project:

$ projmod -s -K rcap.max-rss=512MB user.apache

This will add a new entry similar to the following to the project database, which is stored in the file /etc/project:

$ grep user.apache /etc/project

Once a project is configured, you can enforce a memory cap in two ways (there may be more, but these are the two methods I have come across while reading the RM documentation). The first method uses the newtask utility to start a process in a project that has been configured with memory caps. The following example shows how to start the apache web server in the user.apache project, which was configured above:

$ /usr/bin/newtask -p user.apache /home/apps/apache/httpd/bin/httpd -k start

The second way to enforce a memory cap is to force a user to establish a new login session. If the user has been added to the project database, they will inherit the resource controls that are associated with their user id in /etc/project. To view the project a user is assigned to, the id command can be run with the “-p” option:

$ su – apache
Sun Microsystems Inc. SunOS 5.10 Generic January 2005

$ id -p
uid=103(apache) gid=1(other) projid=100(user.apache)

Once a process is started and associated with a project that has memory caps configured, you can use the rcapstat utility to monitor memory usage, and the paging activity that occurs due to the processes in the project utilizing more memory than has been alloted to them:

$ rcapstat 10

    id project         nproc    vm   rss   cap    at avgat    pg avgpg
   100 user.apache        15  266M  164M  512M    0K    0K    0K    0K
   101 user.mysql          1   59M   11M  256M    0K    0K    0K    0K
    id project         nproc    vm   rss   cap    at avgat    pg avgpg
   100 user.apache        15  266M  164M  512M    0K    0K    0K    0K
   101 user.mysql          1   59M   11M  256M    0K    0K    0K    0K

Memory caps are super useful, but they do have a few issues. The biggest issue is that shared memory is not accounted for properly, so processes that use shared memory can suck up more memory that the amount configured in the memory cap. The second issue is that you can’t use memory caps in the global zone to limit how much memory is used in a local zone. Both of these issues are being worked on by Sun, and hopefully a fix will be out in the coming months.

1 thought on “Capping a Solaris processes memory”

  1. Nice article. When a mem cap is set (say 512MB), is it a cap for a project or for each process in a project? If latter, Is there a way to set a cap for a project such that the accumulated mem usage by all the processes in a project cannot exceed that limit?

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