I've been using gnu/linux as my main daily work system for about 12 years, and
been using Ubuntu since Feisty (2007?). Some of my games have even made it
into the repository. Ubuntu's great stuff.
Every once in a while, in my work, or due to a leak/bug in some application
(e.g., Firefox), one process will start allocating an unexpected amount of
memory. For example, if I try to process too big of an image by accident with
ImageMagick. As the process demands more memory, the kernel tries to provide
it. Other processes, including system critical ones, get swapped out. This
renders the system almost completely unresponsive. Of course, as the user, you
realize what's going on and try to kill the process. But sometimes, when Xorg
gets swapped out, and your terminal shell gets swapped out, and the mouse
stutters... well, you can't really do anything. Sometimes, if it gets really
bad (like two processes in a swap war), even virtual terminals (cntrl-alt-F4,
e.g.) can't properly log in. Some keyboards (like mine!) don't have a SysRq
key. Sometime, hitting the power button is the only solution.
Obviously, this is user or programmer error. Tons of people online claim this
is "normal" behavior. But consider the end-user experience---frustrating even
for the power-user. Yes, this happens on OSX and Windows sometimes too, but...
you know, Linux can do better than that! It should be rock solid no matter
what your processes do.
If you look at how the kernel handles CPU hogging processes, it hardly affects
the system responsiveness at all (great!). But when it comes to RAM-hogging
processes, the kernel allows one process to dominate, by default. And
/etc/security/limits.conf has been de-toothed since 2.4.30 to ignore the rss
limit that could help with this problem (and limits.conf ships with all limits
off by default anyway).
Enter the new (as of 2.6.24) kernel feature: cgroups
Here, we can set a hard RSS limit for all processes of a given user, or even
group of users. A limit on the total. Which is actually what we want, and
better than a per-process limit. If a user spawns several memory-hungry
processes at the same time, a per-process limit would still allow Xorg to get
swapped out. But a group limit can ensure there's always some physical RAM
left for critical (root-owned) processes.
I've tried cgroups on my system (basically setting a limit for myself that is a
portion of my physical RAM, leaving enough RAM for system critical processes
always). And the results are DRAMATIC. No matter what I do, the system never
becomes unresponsive now. Even in the biggest swap war between MY processes, I
can still switch virtual desktops instantly, switch windows, kill a process,
etc.
After 12 years of suffering from this occasional (and pretty much only)
instability of Linux, I think I've finally fixed it.
Of course, I had to install libcgroup1 and cgroup-bin, which weren't there by
default. And I had to study the (extremely complicated) cgroup documentation
to get this setup for myself. Unlikely that most users are going to go out of
their way to set this up.
FINALLY, after all that background, here's my suggestion:
Why isn't this the DEFAULT configuration for desktop users? Set some fraction
of physical RAM aside for system-critical processes, and then give the users
the rest with a cgroup. Then, the user's system would never become
unresponsive due to user error. And I can't think of a situation when you'd
really WANT to have all physical RAM devoted to a user process at the expense
of system-critical processes. At least not in a desktop environment.
You know, the default Ubuntu behavior is not to dump core files (so as not to
waste disk space of unsuspecting users). I think all non-root user processes
should be in a RAM-limited cgroup as default Ubuntu behavior (so as to never
cause unsuspecting users to reach for the power button as a last resort).
Thoughts?
And pasted below is a description of what I did (on my 512MB system). Simple,
assuming you can figure out how to do it.
Thanks for your time,
Jason
$ sudo apt-get install libcgroup1 cgroup-bin
Then, edit /etc/cgconf.conf to add a new control group:
group regularUsers {
memory {
memory.limit_in_bytes = 256M;
}
}
Then, edit /etc/cgrules.conf to add a given user to the regularUsers group:
jasonrohrer memory regularUsers/
Finally, restart cgroups (or reboot):
$ sudo service cgconfig restart
$ sudo service cgred restart
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