[Oracle] ORA-00845 : MEMORY TARGET not supported on this system2

I used Oracle 11g in CentOS VM image. this image is allocated 16GB memory. But after reducing memory to 8GB, oracle instance was not started.

1. Create pfile from spfile

cd $ORACLE_HOME/dbs

sqlplus / as sysdba

CREATE pfile='[PFILE_NAME]' from spfile='[SPFILE_NAME]'

2. Edit pfile

$> vi myinit.ora

3. Startup as pfile

$> sqlplus / as sysdba

startup pfile='[PFILE_NAME]';

4. Create sfpile from pfile

create spfile'spfile[INSTANCE_NAME].ora' from pfile'[PFILE_NAME]';