[Discuss] memory management

[slitt at troubleshooters.com (Steve Litt)]

On Tue, 23 Jun 2015 11:38:30 -0400
Matthew Gillen <me at mattgillen.net> wrote:

> On 06/23/2015 10:18 AM, John Abreau wrote:
> > A bit of googling turned up a page about using cgroups to limit
> > firefox's memory usage.
> > 
> > http://jlebar.com/2011/6/15/Limiting_the_amount_of_RAM_a_program_can_use.html
> 
> 
> ulimit, and prlimit could do the trick I suppose, but the hard-limits
> there would be quite a bit of use-case-specific tuning.
> CGroups are much closer to what I want, but not for the rogue
> processes: I think making a cgroup for core processes and setting
> their swappiness to zero actually gets me closer to what I'm looking
> for.
> 
> What I really wanted was the rogue process to pay the cost of memory
> access, instead of spreading that pain throughout the system.  But
> CGroups gets me close I think:
> 
> According to this:
>  https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Resource_Management_Guide/sec-memory.html
> 
> you can create a group, and set swappiness and oom-killer eligibility
> for that group.  So ideally I would put certain critical things needed
> for recovery (e.g. ssh daemon, agetty, maybe even the window manager;
> any process that allows me to find and kill what I need to help the
> system recover) in a group that would effectively exempt them from the
> thrashing.
> 
> HOWEVER, there is still a problem. For instance, my current system
> doesn't actually launch an 'agetty' (login) process on the virtual
> terminals until you switch to them.  That means you need some
> 'reserved' memory, which my quick reading of cgroups doesn't seem to
> allow you to do.  I'd be happy if there were just a small amount of
> memory reserved, enough to:
>  - launch agetty and login
>  - launch root's login shell
>  - run killall eclipse

Wait a minute. Once upon a time I had a daemon for almost this same use
case, but it was for rogue dbus-daemons instead of rogue eclipses or
rogue firefoxes.

It doesn't even need to be a daemon. You could run it every 5 seconds
with cron, and if twice in a row it shows evidence of a rogue eclipse,
it killalls eclipse. Same with firefox, etc. With firefox, I'd
recommend killall plugin-container first, because that's the usual
subject, and you can keep your windows so you know which to bookmark.

To do this, you need the following:

* A command to define runaway eclipse. Probably some sort of parsed ps
  command.

* A file to store the last value of Eclipse's "runaway value", so you
  can tell whether it's two in a row.

* A script to combine the preceding with a killall

* Connecting the preceding script to cron. Every 5 seconds ought to do
  it.

HTH,

SteveT

Steve Litt 
June 2015 featured book: The Key to Everyday Excellence
http://www.troubleshooters.com/key