Setting memory consumption limits with Upstart - process

Question

I've recently become quite fond of Upstart. Previously I've been using God, Monit and Bluepill but I don't really like these solutions so I'm giving Upstart a try.
I've been using the Foreman gem to generate some basic Upstart configuration files for my processes in /etc/init. However, these generated files only handle the respawning of a crashed process. I was wondering whether it's possible to tell Upstart to restart a process that's consuming for example > 150mb of memory, as you would with Monit, God or Bluepill.
I read through the Upstart docs and this looks like the thing I'm looking for. Though I have no clue how to config something like this.
What I basically want is quite simple. I want to restart my web process if the memory usage is > 150mb ram. These are the files I have:
|-- myapp-web-1.conf
|-- myapp-web-2.conf
|-- myapp-web-3.conf
|-- myapp-web.conf
|-- myapp.conf
And their contents are:
myapp.conf
pre-start script
bash << "EOF"
mkdir -p /var/log/myapp
chown -R deployer /var/log/myapp
EOF
end script
myapp-web.conf
start on starting myapp
stop on stopping myapp
myapp-web-1.conf / myapp-web-2.conf / myapp-web-3.conf
start on starting myapp-web
stop on stopping myapp-web
respawn
exec su - deployer -c 'cd /var/applications/releases/20110607140607; cd myapp && bundle exec unicorn -p $PORT >> /var/log/myapp/web-1.log 2>&1'
Any help much appreciated!

Answer 1

Appending this to the end of myapp-web-*.conf will cause any allocation calls trying to allocate more than 150mb of memory to return ENOMEM:
limit rss 157286400 157286400
The process might crash at this point, or it might not. That's up to the process!
Here's a test for this in the Upstart Source.

Answer 2

From the Upstart docs, the limits come from the rlimit system call options. (http://upstart.ubuntu.com/cookbook/#limit)
Since Linux 2.4+ setting the rss (Resident Set Size) has no effect.
An alternative already suggested in other answers is as which sets the virtual memory Address Space size limits. This will have a very different effect of setting 'real' memory limits.
limit as <soft limit> <hard limit>
Excerpt from man pages for setrlimit:
RLIMIT_AS
The maximum size of the process's virtual memory (address space) in bytes. This limit affects calls to brk(2), mmap(2), and mremap(2),
which fail with the error ENOMEM upon exceeding this limit. Also automatic stack expansion will fail (and generate a SIGSEGV that
kills the process if no alternate stack has been made available via sigaltstack(2)). Since the value is a long, on machines with a
32-bit long either this limit is at most 2 GiB, or this resource is unlimited.