During upgrades Bundler uses a lot of memory in relation to the rest of the installation during the assets precompilation. This would hint at some VM object refcount thing not releasing the touched objects (files having been read in?) and thus the GC not firing and doing its job. Most likely this is an artefact of either Bundler itself or the Rails asset pipeline.
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
3952 1000 20 0 3636888 651740 14836 R 86,8 31,8 2:23.24 bundle
3433 1000 20 0 1681992 190036 4776 S 0,0 9,3 0:05.55 ruby
3403 1000 20 0 1688156 172824 4812 S 0,0 8,4 0:05.95 ruby
3391 1000 20 0 1687128 143528 5100 S 0,0 7,0 0:05.95 ruby
3366 1000 20 0 510236 105780 4528 S 0,3 5,2 0:02.84 ruby
2920 1000 20 0 465132 92584 6804 S 0,0 4,5 0:11.59 ruby
For your consideration to maybe take a deeper look at this, as it is causing annoying shuffling for sysadmins with other processes on servers at upgrade times if the servers are provisioned for the runtime memory requirements.