Free memory in server and session PGA memory

Hi Friends,

Environment : Solaris 10 , oracle 11.2.0.2

We have our production databases monitored by the BMC portal application. We 
often get alerts and warnings on free memory on the server. Say my server has 
24 GB physical memory, we will get an alert when it comes down 2.4GB which is 
10%. 

We troubleshoot this starting with vmstat command and we can see the 'free' 
part in vmstat do report a value less than 3 GB. This server is part of a two 
node rac which hosts two databases. If I do a ps command sort on pmem I can see 
that the processes consuming most memory  ( which has pmem field , which is a 
ratio as 4 - 5 ) are oracle server processes ( oracle<ORACLE_SID>(LOCAL=NO)). 
Now IF I check what these processes are  doing I can see that these are coming 
from jdbc thin client ( yes, we use weblogic). Most of these sessions coming 
top in ps command are now INACTIVE. So my understanding is that these are app 
server connections which were once took for doing something and later released 
to connection pool. The question here are

1. Why memory taken by these processes ( of course from PGA ) are not released 
to OS after use. 
2. I understand this is default weblogic behavior of keeping connections in 
pool and use them when they need. But considering memory associated with these 
are still not released to OS , is this an efficient way ?
3. If I check the wait event of these INACTIVE sessions they have ' SQL Net 
wait '. Again , is this a good behavior from weblogic ?
4. I have also run Tanel's procmm and noticed the Anon memory almost equals to 
'PGA used by this session' from v$sesstat which again confirms that 'unused 
memory' ( once used) is still associated with the process.  

I would like to get help from experts who might have already thought about this 
and will have answer to my questions, which in a way may not e relevant. 

PS : I already have an SR open for which I did not get a proper response.  

Best Regards,
Sreejith
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