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# Copyright 2021 The Matrix.org Foundation C.I.C.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import ctypes
import logging
import os
import re
from typing import Iterable, Optional
from prometheus_client import Metric
from synapse.metrics import REGISTRY, GaugeMetricFamily
logger = logging.getLogger(__name__)
def _setup_jemalloc_stats() -> None:
"""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.
# We look in `/proc/self/maps`, which only exists on linux.
if not os.path.exists("/proc/self/maps"):
logger.debug("Not looking for jemalloc as no /proc/self/maps exist")
return
# 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("/proc/self/maps") as f:
for line in f:
match = regex.search(line.strip())
if match:
jemalloc_path = match.group()
if not jemalloc_path:
# No loaded jemalloc was found.
logger.debug("jemalloc not found")
return
logger.debug("Found jemalloc at %s", jemalloc_path)
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 as e:
logger.warning("Failed to reload jemalloc stats: %s", e)
class JemallocCollector:
"""Metrics for internal jemalloc stats."""
def collect(self) -> Iterable[Metric]:
_jemalloc_refresh_stats()
g = GaugeMetricFamily(
"jemalloc_stats_app_memory_bytes",
"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 as e:
# There was an error fetching the value, skip.
logger.warning("Failed to read jemalloc stats.%s: %s", t, e)
continue
g.add_metric([t], value=value)
yield g
REGISTRY.register(JemallocCollector())
logger.debug("Added jemalloc stats")
def setup_jemalloc_stats() -> None:
"""Try to setup jemalloc stats, if jemalloc is loaded."""
try:
_setup_jemalloc_stats()
except Exception as e:
# This should only happen if we find the loaded jemalloc library, but
# fail to load it somehow (e.g. we somehow picked the wrong version).
logger.info("Failed to setup collector to record jemalloc stats: %s", e)
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