Bouncing Oracle db does not give back memory! is this correct?

I changed the memory_max_target and memory_target parameters and bounce the db. And nothing changed.

There maybe two causes: Oracle really doesn't give back the memory allocated. Or some other memory eating processes released what they kept after the restart.

Rebooting the machine helped, total memory utilized decreased. This may be because Oracle kept the memory allocated, or the filecache_max, filecache_min parameters' usage of HP-UX also decreased after reboot. Bouncing the db most probably let OS to take back the memory used by Oracle. After some time, again the OS memory utilization ate up the memory. So, Oracle is innocent, it had already given the memory blocks. OS parameters: filecache_max and filecache_min is the root cause of the problem.

Excerpt from Guy Harrison:

"We might deal with today’s pain but fail to achieve a permanent or scalable solution." matches our case as we need to define  the root cause of the problem, not just descreasing the SGA memory utilization, and sit back.