tools/lib/uobjnew_example.txt

Demonstrations of uobjnew.


uobjnew summarizes new object allocation events and prints out statistics on
which object type has been allocated frequently, and how many bytes of that
type have been allocated. This helps diagnose common allocation paths, which
can in turn cause heavy garbage collection.

For example, trace Ruby object allocations when running some simple commands
in irb (the Ruby REPL):

# ./uobjnew -l ruby 27245
Tracing allocations in process 27245 (language: ruby)... Ctrl-C to quit.

TYPE                           # ALLOCS      # BYTES
NameError                             1            0
RubyToken::TkSPACE                    1            0
RubyToken::TkSTRING                   1            0
String                                7            0
RubyToken::TkNL                       2            0
RubyToken::TkIDENTIFIER               2            0
array                                55          129
string                              344         1348
^C


Plain C/C++ allocations (through "malloc") are also supported. We can't report
the type being allocated, but we can report the object sizes at least. Also,
print only the top 10 rows by number of bytes allocated:

# ./uobjnew -S 10 -l c 27245
Tracing allocations in process 27245 (language: c)... Ctrl-C to quit.

TYPE                           # ALLOCS      # BYTES
block size 64                        22         1408
block size 992                        2         1984
block size 32                        68         2176
block size 48                        48         2304
block size 944                        4         3776
block size 1104                       4         4416
block size 160                       32         5120
block size 535                       15         8025
block size 128                      112        14336
block size 80                       569        45520
^C


USAGE message:

# ./uobjnew -h
usage: uobjnew.py [-h] [-l {c,java,ruby,tcl}] [-C TOP_COUNT] [-S TOP_SIZE] [-v]
                  pid [interval]

Summarize object allocations in high-level languages.

positional arguments:
  pid                   process id to attach to
  interval              print every specified number of seconds

optional arguments:
  -h, --help            show this help message and exit
  -l {c,java,ruby,tcl}, --language {c,java,ruby,tcl}
                        language to trace
  -C TOP_COUNT, --top-count TOP_COUNT
                        number of most frequently allocated types to print
  -S TOP_SIZE, --top-size TOP_SIZE
                        number of largest types by allocated bytes to print
  -v, --verbose         verbose mode: print the BPF program (for debugging
                        purposes)

examples:
    ./uobjnew -l java 145         # summarize Java allocations in process 145
    ./uobjnew -l c 2020 1         # grab malloc() sizes and print every second
    ./uobjnew -l ruby 6712 -C 10  # top 10 Ruby types by number of allocations
    ./uobjnew -l ruby 6712 -S 10  # top 10 Ruby types by total size