casper configures system to use 50% ram for compressed swap post installation

More information as to how Casper ended up on my laptop:

I installed the usb-creator on Oneiric, which required lupin-capser, which pulled in casper. I upgrade from Oneiric to Precise on 2012-01-07. On 2012-02-01, my host picked up the version of Casper which has the compcache setting.

casper is not installed on the target system during the installation process and afaict usb-creator doesn't require capser or lupin-casper so I'm really not sure what happened to your system.

Additionally, compcache (according to the casper changelog) should only be used on systems (running casper) with less than 512MB of ram.

casper (1.232) lucid; urgency=low

  * bump compcache size to 50% on live images for machines with less than
    512MiB. This makes sure we don't hit OOM errors on systems with only
    256MiB of RAM.

 -- Oliver Grawert <email address hidden> Mon, 12 Apr 2010 08:10:06 +0200

It might make sense to do an additional run-time check to see if you booted with boot=casper, and otherwise not set this variable.

i am closing this bug for two reasons:

a) having compcache enabled isnt actually a bad thing, it raises the amount of usable ram with no known drawbacks (and i dont know what you refer to regarding a "poor experience")
b) on normal installs casper is not installed, during installation casper (and with it the compcache configuration) gets removed by ubiquity

To elaborate on Oli's "no known drawbacks" comment, I think it's clear that some people don't understand how zram works. While you're telling it that you can use up to 50% of your RAM for compressed swap, that doesn't actually kick in until you run out of RAM, precisely the point where you'd normally be hitting disk for swap instead.

So, if you only ever commit 3.9G on a 4G system, zram does essentially nothing. If you overcommit, it'll start swapping from ram to zram and eating memory, but this all happens so much faster than you can swap to disk that I have yet to see it be a bad thing (in fact, I've been arguing for a while that we should just enable zram on all machines, regardless of configuration).

I encountered the same thing here. Remastersys required casper, and casper set the compcache to 50%.

Regardless of the fact that it may be a good thing performance wise, I still think it's not something that should happen without the user's knowledge.

I had to waste quite a bit of time to find out what was the source of the 50% zram swap partition. Also, I would assume this can affect those who want to/can otherwise use hibernate, since this is not a non volatile swap partition.

"Additionally, compcache (according to the casper changelog) should only be used on systems (running casper) with less than 512MB of ram."

I have 5.5 GB of available RAM. Casper apparently isn't using that 512MB limit, or fails to determine the system's available memory properly.