Memory used by oracle

[Alba]

Hello,

I have a server running Oracle 10g on a RHEL 5.3. I need to determine how
much memory Oracle is using but I ran into some problems while trying to do
that with the shared memory segments.

[root at abcserver ~]# free -m
             total       used       free     shared    buffers     cached
Mem:          8988       8906         82          0        102       5411
-/+ buffers/cache:       3392       5596
Swap:         3999       1577       2422

[root at abcserver ~]# ipcs -m

------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status
0x0a008088 0          root      666        4096       2
0x1400808a 32769      root      666        4          0
0x0400808a 65538      root      600        4096       0
0x0a159d08 98307      oracle    640        132120576  19
0x1f361e94 131076     oracle    660        1612709888 57
0x781df938 163845     oracle    660        4297064448 51
0xefdb0bf8 229382     oracle    660        1033895936 283


If I add up the sizes of the shared segments for the oracle processes I get
that they are using aroung 6.6 Gb of memory alone... and that is not
including non-shared memory segments. My biggest issue is that from the free
command I get that the system is using around 5Gb (Mem used - Mem cached +
swap used). What am I doing wrong in here?

What would be the best way to estimate how much memory a given user is using
if we know that the processes on the system do have heavy shared memory
segments?

Thanks in advance.

Alba