Comment 12 for bug 182960

Note that as of oneiric, pam_limits directly probes the kernel for default limits to set (by reading /proc/1/limits), and it is our stated policy that pam_limits should not impose any policy by default other than the one given by the kernel itself. As such, though a feature to allow specifying memory limits as a percentage in limits.conf may be useful:

 - this should be submitted upstream first rather than being applied as a patch in Ubuntu
 - the default limits.conf shipped in Ubuntu will not use this feature, even if present.

If your aim is to get limits applied by default, please submit a patch to the kernel instead. The kernel already sets several default limits based on available system resources, so there's no problem in principle with doing the same thing for memory limits (though the exact limit chosen will have to be justified to upstream).