Hi

You can check sga free by the following.

select name,
sgasize/1024/1024 "Allocated (M)",
bytes/1024/1024 "Free (K)",
round(bytes/sgasize*100, 2) "% Free"
from (select sum(bytes) sgasize from sys.v_$sgastat) s, sys.v_$sgastat f
where f.name = 'free memory'
/