abap/objmgr/tracelevel is a SAP Parameter attribute which is used to control ABAP Objects Object Manager Trace Level information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
Only for internal use by SAP Support / for error diagnosis
This parameter controls the TRACE output of the ABAP Objects Garbage
Collector (which is transferred to the trace file dev_w*) and the
measurement of the performance values for the Garbage Collector (which
are displayed under 'System Areas' -> 'OBJMGR').
= 0
No output, GC overhead is not measured
= 1
GC performance is measured and displayed in 'OBJMGR'
= 2
TRACE for start, each step, and end of a Garbage Collector.
= 3
TRACE 'ABAPStart/End'
See SAP Parameter Documentation for full SAP documentation for this profile parameter.