Sessions and processes issue

Using oracle 10.2.0.3 on Linux 64

here is the SQL I used to find processes not matching sessions
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SQL> select inst_id,count(*) from gv$process where (inst_id,addr) not in (select inst_id,paddr from gv$session) group by rollup(inst_id) ;

INST_ID COUNT(*)
---------- ----------
1 3
2 3
3 6
12
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Is this correct?
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Yesterday before the server crash I saw values of up to 1600 for INST_ID = 2. At that moment 2100 - 2200 processes ran on the server (checked with ps -ef | grep oracle | wc -l and gv$process).
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Now I'm concerned about processes having no sessions and what they are doing. I didn't have the possibility to check a particular process with strace or tracing it with ORACLE. Please comment on this.