The 11g AMM feature is enabled by the MEMORY_TARGET / MEMORY_MAX_TARGET
instance initialization parameters. That is also the case with a default
database instance created using Database Configuration Assistant (DBCA).
With AMM all SGA memory is allocated by creating files under /dev/shm. When Oracle DB does SGA allocations that way HugePages are not reserved/used. The use of AMM is absolutely incompatible with HugePages.
Please also note that ramfs (instead of tmpfs mount over /dev/shm) is not supported for AMM at all. With AMM the Oracle database needs to grow and reduce the size of SGA dynamically. This is not possible with ramfs where it possible and supported with tmpfs (which is the default for the OS installation).
If you want to use HugePages make sure that both MEMORY_TARGET / MEMORY_MAX_TARGET initialization parameters are unset (i.e. using "ALTER SYSTEM RESET") for the database instance.
