database SGA size is not shown as reserved into memory server

Hi:

I am migrating my database from AIX 7.1 to AIX 7.2. My database is standard edition release is 11.2.0.4

the  question is that when I started up database in AIX 7.2 memory server just increase use at 1GB

I mean, according to memory SO monitor, SO is using 4GB, when I start up database, which has been defined to use 20GB,

SO monitor just register 5GB used into memory, it is just 1GB more, when the expeted was it increased on 20GB.

I have review pre-install tasks for oracle and all kernel parameter on operating system are agree with document

if someone has any idea what I can do ...