interpretation of ipcs -m command

Hello experts,

                        I am trying to interpret below ipcs command.

[oracle@xdhfd5cn02 doc]$ ipcs -m

------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status
0x90e155f0 4554756    grid      660        4096       0
0x62de3f90 5603333    oracle    660        22550675456 148
0xc5c497f8 5668870    oracle    660        4096       0

So according to nattach column 148 process is attached with oracle which is using shared memory segment.My understanding is that this 148 process are server process not the user process.Based on that when i use

ps -ef | grep ora_ it gives me below number

 ps -ef | grep ora_ | wc -l
174
Which is not matching with ipcs -m output.Can anyone help me to understand this?