diff options
| -rw-r--r-- | changelog.d/9882.misc | 1 | ||||
| -rw-r--r-- | synapse/metrics/__init__.py | 161 |
2 files changed, 162 insertions, 0 deletions
diff --git a/changelog.d/9882.misc b/changelog.d/9882.misc new file mode 100644 index 0000000000..facfa31f38 --- /dev/null +++ b/changelog.d/9882.misc @@ -0,0 +1 @@ +Export jemalloc stats to Prometheus if it is being used. diff --git a/synapse/metrics/__init__.py b/synapse/metrics/__init__.py index 31b7b3c256..13be0b9b96 100644 --- a/synapse/metrics/__init__.py +++ b/synapse/metrics/__init__.py @@ -12,12 +12,15 @@ # See the License for the specific language governing permissions and # limitations under the License. +import ctypes +import ctypes.util import functools import gc import itertools import logging import os import platform +import re import threading import time from typing import Callable, Dict, Iterable, Optional, Tuple, Union @@ -597,6 +600,163 @@ def runUntilCurrentTimer(reactor, func): return f +def _setup_jemalloc_stats(): + """Checks to see if jemalloc is loaded, and hooks up a collector to record + statistics exposed by jemalloc. + """ + + # Try to find the loaded jemalloc shared library, if any. We need to + # introspect into what is loaded, rather than loading whatever is on the + # path, as if we load a *different* jemalloc version things will seg fault. + pid = os.getpid() + + # We're looking for a path at the end of the line that includes + # "libjemalloc". + regex = re.compile(r"/\S+/libjemalloc.*$") + + jemalloc_path = None + with open(f"/proc/{pid}/maps") as f: + for line in f.readlines(): + match = regex.search(line.strip()) + if match: + jemalloc_path = match.group() + + if not jemalloc_path: + # No loaded jemalloc was found. + return + + jemalloc = ctypes.CDLL(jemalloc_path) + + def _mallctl( + name: str, read: bool = True, write: Optional[int] = None + ) -> Optional[int]: + """Wrapper around `mallctl` for reading and writing integers to + jemalloc. + + Args: + name: The name of the option to read from/write to. + read: Whether to try and read the value. + write: The value to write, if given. + + Returns: + The value read if `read` is True, otherwise None. + + Raises: + An exception if `mallctl` returns a non-zero error code. + """ + + input_var = None + input_var_ref = None + input_len_ref = None + if read: + input_var = ctypes.c_size_t(0) + input_len = ctypes.c_size_t(ctypes.sizeof(input_var)) + + input_var_ref = ctypes.byref(input_var) + input_len_ref = ctypes.byref(input_len) + + write_var_ref = None + write_len = ctypes.c_size_t(0) + if write is not None: + write_var = ctypes.c_size_t(write) + write_len = ctypes.c_size_t(ctypes.sizeof(write_var)) + + write_var_ref = ctypes.byref(write_var) + + # The interface is: + # + # int mallctl( + # const char *name, + # void *oldp, + # size_t *oldlenp, + # void *newp, + # size_t newlen + # ) + # + # Where oldp/oldlenp is a buffer where the old value will be written to + # (if not null), and newp/newlen is the buffer with the new value to set + # (if not null). Note that they're all references *except* newlen. + result = jemalloc.mallctl( + name.encode("ascii"), + input_var_ref, + input_len_ref, + write_var_ref, + write_len, + ) + + if result != 0: + raise Exception("Failed to call mallctl") + + if input_var is None: + return None + + return input_var.value + + def _jemalloc_refresh_stats() -> None: + """Request that jemalloc updates its internal statistics. This needs to + be called before querying for stats, otherwise it will return stale + values. + """ + try: + _mallctl("epoch", read=False, write=1) + except Exception: + pass + + class JemallocCollector: + """Metrics for internal jemalloc stats.""" + + def collect(self): + _jemalloc_refresh_stats() + + g = GaugeMetricFamily( + "jemalloc_stats_app_memory", + "The stats reported by jemalloc", + labels=["type"], + ) + + # Read the relevant global stats from jemalloc. Note that these may + # not be accurate if python is configured to use its internal small + # object allocator (which is on by default, disable by setting the + # env `PYTHONMALLOC=malloc`). + # + # See the jemalloc manpage for details about what each value means, + # roughly: + # - allocated ─ Total number of bytes allocated by the app + # - active ─ Total number of bytes in active pages allocated by + # the application, this is bigger than `allocated`. + # - resident ─ Maximum number of bytes in physically resident data + # pages mapped by the allocator, comprising all pages dedicated + # to allocator metadata, pages backing active allocations, and + # unused dirty pages. This is bigger than `active`. + # - mapped ─ Total number of bytes in active extents mapped by the + # allocator. + # - metadata ─ Total number of bytes dedicated to jemalloc + # metadata. + for t in ( + "allocated", + "active", + "resident", + "mapped", + "metadata", + ): + try: + value = _mallctl(f"stats.{t}") + except Exception: + # There was an error fetching the value, skip. + continue + + g.add_metric([t], value=value) + + yield g + + REGISTRY.register(JemallocCollector()) + + +try: + _setup_jemalloc_stats() +except Exception: + logger.info("Failed to setup collector to record jemalloc stats.") + try: # Ensure the reactor has all the attributes we expect reactor.seconds # type: ignore @@ -615,6 +775,7 @@ try: except AttributeError: pass + __all__ = [ "MetricsResource", "generate_latest", |