From c0268e8d1f450e286fc55e77f53a9ede6b72acab Mon Sep 17 00:00:00 2001 From: Joseph Schuchart Date: Thu, 24 Oct 2013 10:10:51 -0300 Subject: [PATCH] perf script python: Fix mem leak due to missing Py_DECREFs on dict entries We are using the Python scripting interface in perf to extract kernel events relevant for performance analysis of HPC codes. We noticed that the "perf script" call allocates a significant amount of memory (in the order of several 100 MiB) during it's run, e.g. 125 MiB for a 25 MiB input file: $> perf record -o perf.data -a -R -g fp \ -e power:cpu_frequency -e sched:sched_switch \ -e sched:sched_migrate_task -e sched:sched_process_exit \ -e sched:sched_process_fork -e sched:sched_process_exec \ -e cycles -m 4096 --freq 4000 $> /usr/bin/time perf script -i perf.data -s dummy_script.py 0.84user 0.13system 0:01.92elapsed 51%CPU (0avgtext+0avgdata 125532maxresident)k 73072inputs+0outputs (57major+33086minor)pagefaults 0swaps Upon further investigation using the valgrind massif tool, we noticed that Python objects that are created in trace-event-python.c via PyString_FromString*() (and their Integer and Long counterparts) are never free'd. The reason for this seem to be missing Py_DECREF calls on the objects that are returned by these functions and stored in the Python dictionaries. The Python dictionaries do not steal references (as opposed to Python tuples and lists) but instead add their own reference. Hence, the reference that is returned by these object creation functions is never released and the memory is leaked. (see [1,2]) The attached patch fixes this by wrapping all relevant calls to PyDict_SetItemString() and decrementing the reference counter immediately after the Python function call. This reduces the allocated memory to a reasonable amount: $> /usr/bin/time perf script -i perf.data -s dummy_script.py 0.73user 0.05system 0:00.79elapsed 99%CPU (0avgtext+0avgdata 49132maxresident)k 0inputs+0outputs (0major+14045minor)pagefaults 0swaps For comparison, with a 120 MiB input file the memory consumption reported by time drops from almost 600 MiB to 146 MiB. The patch has been tested using Linux 3.8.2 with Python 2.7.4 and Linux 3.11.6 with Python 2.7.5. Please let me know if you need any further information. [1] http://docs.python.org/2/c-api/tuple.html#PyTuple_SetItem [2] http://docs.python.org/2/c-api/dict.html#PyDict_SetItemString Signed-off-by: Joseph Schuchart Reviewed-by: Tom Zanussi Cc: Paul Mackerras Cc: Peter Zijlstra Cc: Tom Zanussi Link: http://lkml.kernel.org/r/1381468543-25334-4-git-send-email-namhyung@kernel.org Signed-off-by: Arnaldo Carvalho de Melo --- .../scripting-engines/trace-event-python.c | 37 ++++++++++++------- 1 file changed, 24 insertions(+), 13 deletions(-) diff --git a/tools/perf/util/scripting-engines/trace-event-python.c b/tools/perf/util/scripting-engines/trace-event-python.c index cc75a3cef388..95d91a0b23af 100644 --- a/tools/perf/util/scripting-engines/trace-event-python.c +++ b/tools/perf/util/scripting-engines/trace-event-python.c @@ -56,6 +56,17 @@ static void handler_call_die(const char *handler_name) Py_FatalError("problem in Python trace event handler"); } +/* + * Insert val into into the dictionary and decrement the reference counter. + * This is necessary for dictionaries since PyDict_SetItemString() does not + * steal a reference, as opposed to PyTuple_SetItem(). + */ +static void pydict_set_item_string_decref(PyObject *dict, const char *key, PyObject *val) +{ + PyDict_SetItemString(dict, key, val); + Py_DECREF(val); +} + static void define_value(enum print_arg_type field_type, const char *ev_name, const char *field_name, @@ -279,11 +290,11 @@ static void python_process_tracepoint(union perf_event *perf_event PyTuple_SetItem(t, n++, PyInt_FromLong(pid)); PyTuple_SetItem(t, n++, PyString_FromString(comm)); } else { - PyDict_SetItemString(dict, "common_cpu", PyInt_FromLong(cpu)); - PyDict_SetItemString(dict, "common_s", PyInt_FromLong(s)); - PyDict_SetItemString(dict, "common_ns", PyInt_FromLong(ns)); - PyDict_SetItemString(dict, "common_pid", PyInt_FromLong(pid)); - PyDict_SetItemString(dict, "common_comm", PyString_FromString(comm)); + pydict_set_item_string_decref(dict, "common_cpu", PyInt_FromLong(cpu)); + pydict_set_item_string_decref(dict, "common_s", PyInt_FromLong(s)); + pydict_set_item_string_decref(dict, "common_ns", PyInt_FromLong(ns)); + pydict_set_item_string_decref(dict, "common_pid", PyInt_FromLong(pid)); + pydict_set_item_string_decref(dict, "common_comm", PyString_FromString(comm)); } for (field = event->format.fields; field; field = field->next) { if (field->flags & FIELD_IS_STRING) { @@ -313,7 +324,7 @@ static void python_process_tracepoint(union perf_event *perf_event if (handler) PyTuple_SetItem(t, n++, obj); else - PyDict_SetItemString(dict, field->name, obj); + pydict_set_item_string_decref(dict, field->name, obj); } if (!handler) @@ -370,21 +381,21 @@ static void python_process_general_event(union perf_event *perf_event if (!handler || !PyCallable_Check(handler)) goto exit; - PyDict_SetItemString(dict, "ev_name", PyString_FromString(perf_evsel__name(evsel))); - PyDict_SetItemString(dict, "attr", PyString_FromStringAndSize( + pydict_set_item_string_decref(dict, "ev_name", PyString_FromString(perf_evsel__name(evsel))); + pydict_set_item_string_decref(dict, "attr", PyString_FromStringAndSize( (const char *)&evsel->attr, sizeof(evsel->attr))); - PyDict_SetItemString(dict, "sample", PyString_FromStringAndSize( + pydict_set_item_string_decref(dict, "sample", PyString_FromStringAndSize( (const char *)sample, sizeof(*sample))); - PyDict_SetItemString(dict, "raw_buf", PyString_FromStringAndSize( + pydict_set_item_string_decref(dict, "raw_buf", PyString_FromStringAndSize( (const char *)sample->raw_data, sample->raw_size)); - PyDict_SetItemString(dict, "comm", + pydict_set_item_string_decref(dict, "comm", PyString_FromString(thread->comm)); if (al->map) { - PyDict_SetItemString(dict, "dso", + pydict_set_item_string_decref(dict, "dso", PyString_FromString(al->map->dso->name)); } if (al->sym) { - PyDict_SetItemString(dict, "symbol", + pydict_set_item_string_decref(dict, "symbol", PyString_FromString(al->sym->name)); } -- 2.20.1