I'm writing a daemon that is meant to be used in conjunction with Rik van
Riel's OOM killer patch. The following functionality is planned:
1. Per-user memory quotas
These are overcommitted; a user can exceed the quota so long as
system memory is not low. Think of it as a minimum resource
guarantee. There is a soft and a hard limit. If you exceed the
soft limit when system memory is low, your processes are sent a
SIGSTOP. If you exceed the hard limit, a process is selected and
sent SIGTERM, then SIGKILL. Limits are specified in a
configuration file.
2. Per-task priorities (not in the "nice" priority sense though)
Some tasks should never be signalled, like the X server or a login
shell. Other tasks should be the first to go against the wall and
face the firing squad. If the OOM killer patch is to use this new
task priority, I need to add an int to task_struct and a system
call to allow the daemon to set the priority. This places policy
in user-space, while preventing system crashes when OOM.
3. Execution on task startup
It may be worth having the kernel signal or wake-up the daemon
after a new task is started. I don't know how to do this, and I'm
not sure it's even a good idea. Perhaps instead the daemon should
run as a real-time task?
Number 1 is mostly implemented right now (give me a few days before I
release release the code).
Questions:
1. How can I avoid using stack or library functions, especially doing file
IO? Right now I simply ignore the SIGHUP if system memory is low, but
the daemon still must read the /proc/[PID] files periodically.
2. I use mlockall() with MCL_FUTURE. The man page indicates that there is
a limit to the number of locked pages. Could this be a problem on large
machines, since I allocate several K of memory per user to store data?
Any comments would be appreciated.
Dave
David Whysong dwhysong@physics.ucsb.edu
Astrophysics graduate student University of California, Santa Barbara
My public PGP keys are on my web page - http://www.physics.ucsb.edu/~dwhysong
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