System V IPC Now Managed By Resource Controls

Oct 27, 2008 | 4 minutes read
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Tag: Resource Management

When it comes to Solaris 10, all IPC facilities are either automatically configured or can be controlled by resource controls. In the same time, they get new default values, when applicable.

As an example, we will assume that we need to change the limit on number of shared memory segments that can be created, and that the new default (128) is not enough either. Before Solaris 10, you've had to set the shmsys:shminfo_shmmni tunable parameter in the /etc/system kernel configuration file, which is a system wide limit, and required a reboot. This parameter is now marked as Obsolete or Have Been Removed, and its use is clearly deprecated.

To increase the corresponding limit up to 256 shared memory segments, we now have to deal with the project.max-shm-ids resource control which is controlled at the project level. The idea is to set the appropriate resource control to a project, then execute a program in the context of this project. One method to achieve this is to create a project at one side (using the project(4) database), and to populate the extended user attributes to do the association between this project and a user account (using the user_attr(4) database) in order to put the new project as the default project for the user. Or it is possible not to create an extended user attribute with this project at all, but use its characteristics explicitly through the newtask(1) command (and the login(1), cron(1M), and su(1M) programs, or the setproject(3PROJECT) function). But the simplest method, and the less intrusive one, is certainly to directly put the project as the default one for a user account. Here is how to do so.

By default, no error message is logged against the syslog daemon for resource controls. To be able to see an appropriate message in the messages log file, you must first enable globally the syslog action for the wanted resource control (the default level is notice).

# rctladm -e syslog project.max-shm-ids
# rctladm -l project.max-shm-ids
project.max-shm-ids   syslog=notice   [ no-basic deny count ]

When the limit on the number of shared memory segments is reached, one message similar to the following is write to the log file:

# grep rctl /var/adm/messages
/var/adm/messages:Oct 21 16:47:29 hostname genunix: [ID 883052 kern.notice] privileged rctl project.max-shm-ids (value 128) exceeded by project 3

Here is the definition of the new project, and its configuration.

# getent project user.username
user.username:1000:Project To Increase The Limit Of SHM Segments:::project.max-shm-ids=(priv,256,deny)
# projects -l user.username
      projid : 1000
      comment: "Project To Increase The Limit Of SHM Segments"
      users  : (none)
      groups : (none)
      attribs: project.max-shm-ids=(priv,256,deny)

When a project name begin with the pattern user., the project will automatically be set as the default one for the corresponding user, without the need to populate the extended user attributes database. Check that the project is set as the default project for the account username.

# id -p username
uid=100(username) gid=100(groupname) projid=1000(user.username)
# projects -d username

After a login phase using the username identity, the programs progname is launched. We can confirm the use of shared memory segments under the context of the project user.username, and we can consult the programs statistics report.

# ipcs -mJ
IPC status from  as of Wed Oct 29 11:39:59 CET 2008
T         ID KEY        MODE    OWNER     GROUP       PROJECT
Shared Memory:
m 1409286255   0 --rw-rw-rw- username groupname user.username
m  469762152   0 --rw-rw-rw- username groupname user.username
m         56   0 --rw-rw-rw- username groupname user.username
# prstat -n5 -cJ
  3704 username  373M  284M cpu24   2   10 0:07:37 2.1% progname/26
  6785 username  285M  196M sleep  29   10 0:04:13 1.1% progname/26
  4480 username  785M  697M sleep  29   10 0:11:40 1.1% progname/26
  5836 username  293M  204M sleep  29   10 0:06:31 1.0% progname/26
  7635 username  277M  188M sleep  29   10 0:01:00 0.9% progname/26
  1000       26 6472M 6333M    26%   3:57:24  23% user.username
     1       17   41M   87M   0.4%   2:39:58 0.0% user.root
     0       43  184M  267M   1.1%   4:07:25 0.0% system
     3        4 5856K   11M   0.0%   0:00:00 0.0% default
Total: 90 processes, 916 lwps, load averages: 4.41, 2.36, 1.04

Last, we can verify the new setting for one progname instance. For example for PID 3704:

# prctl -n project.max-shm-ids 3704
process: 3704: bin/progname 54 80 -Xmx192m
        privileged        256       -   deny                -
        system          16.8M     max   deny                -

The resource management facility can do much more than just tuning IPC settings, such as managing CPU usage, and physical memory control. It is a more fine-grained facility than what is in place before Solaris 10, and did not required a reboot anymore.

As a last word, we can note that there are command line tools to help creating and managing projects and extended user attributes for locally stored databases: respectively projadd(1M), projmod(1M), and useradd(1M), usermod(1M). But since the information sources was hosted in NIS and LDAP network directories, we did not use them for this test case though.