After the installation, check memory size like this:
ps -o rss,vsz,cmd --sort=rss -u oracle
The rss column means Resident Set Size i.e. actually occupied virtual memory, the vsz tells us what the total virtual memory size is (including stuff that's swapped away). Check the manpage or go here for more information on ps.
[oracle@bkuik-nl orcl]$ ps -o rss,vsz,cmd --sort=rss -u oracle [oracle@bkuik-nl orcl]$