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Add config flags to allow for cache auto-tuning (#12701)
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changelog.d/12701.feature
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1
changelog.d/12701.feature
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@ -0,0 +1 @@
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Add a config options to allow for auto-tuning of caches.
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@ -784,6 +784,24 @@ caches:
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#
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#cache_entry_ttl: 30m
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# This flag enables cache autotuning, and is further specified by the sub-options `max_cache_memory_usage`,
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# `target_cache_memory_usage`, `min_cache_ttl`. These flags work in conjunction with each other to maintain
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# a balance between cache memory usage and cache entry availability. You must be using jemalloc to utilize
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# this option, and all three of the options must be specified for this feature to work.
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#cache_autotuning:
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# This flag sets a ceiling on much memory the cache can use before caches begin to be continuously evicted.
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# They will continue to be evicted until the memory usage drops below the `target_memory_usage`, set in
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# the flag below, or until the `min_cache_ttl` is hit.
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#max_cache_memory_usage: 1024M
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# This flag sets a rough target for the desired memory usage of the caches.
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#target_cache_memory_usage: 758M
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# 'min_cache_ttl` sets a limit under which newer cache entries are not evicted and is only applied when
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# caches are actively being evicted/`max_cache_memory_usage` has been exceeded. This is to protect hot caches
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# from being emptied while Synapse is evicting due to memory.
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#min_cache_ttl: 5m
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# Controls how long the results of a /sync request are cached for after
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# a successful response is returned. A higher duration can help clients with
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# intermittent connections, at the cost of higher memory usage.
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@ -1119,7 +1119,17 @@ Caching can be configured through the following sub-options:
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with intermittent connections, at the cost of higher memory usage.
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By default, this is zero, which means that sync responses are not cached
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at all.
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* `cache_autotuning` and its sub-options `max_cache_memory_usage`, `target_cache_memory_usage`, and
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`min_cache_ttl` work in conjunction with each other to maintain a balance between cache memory
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usage and cache entry availability. You must be using [jemalloc](https://github.com/matrix-org/synapse#help-synapse-is-slow-and-eats-all-my-ramcpu)
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to utilize this option, and all three of the options must be specified for this feature to work.
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* `max_cache_memory_usage` sets a ceiling on how much memory the cache can use before caches begin to be continuously evicted.
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They will continue to be evicted until the memory usage drops below the `target_memory_usage`, set in
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the flag below, or until the `min_cache_ttl` is hit.
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* `target_memory_usage` sets a rough target for the desired memory usage of the caches.
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* `min_cache_ttl` sets a limit under which newer cache entries are not evicted and is only applied when
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caches are actively being evicted/`max_cache_memory_usage` has been exceeded. This is to protect hot caches
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from being emptied while Synapse is evicting due to memory.
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Example configuration:
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```yaml
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@ -1127,8 +1137,11 @@ caches:
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global_factor: 1.0
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per_cache_factors:
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get_users_who_share_room_with_user: 2.0
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expire_caches: false
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sync_response_cache_duration: 2m
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cache_autotuning:
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max_cache_memory_usage: 1024M
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target_cache_memory_usage: 758M
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min_cache_ttl: 5m
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```
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### Reloading cache factors
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@ -176,6 +176,24 @@ class CacheConfig(Config):
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#
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#cache_entry_ttl: 30m
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# This flag enables cache autotuning, and is further specified by the sub-options `max_cache_memory_usage`,
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# `target_cache_memory_usage`, `min_cache_ttl`. These flags work in conjunction with each other to maintain
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# a balance between cache memory usage and cache entry availability. You must be using jemalloc to utilize
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# this option, and all three of the options must be specified for this feature to work.
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#cache_autotuning:
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# This flag sets a ceiling on much memory the cache can use before caches begin to be continuously evicted.
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# They will continue to be evicted until the memory usage drops below the `target_memory_usage`, set in
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# the flag below, or until the `min_cache_ttl` is hit.
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#max_cache_memory_usage: 1024M
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# This flag sets a rough target for the desired memory usage of the caches.
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#target_cache_memory_usage: 758M
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# 'min_cache_ttl` sets a limit under which newer cache entries are not evicted and is only applied when
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# caches are actively being evicted/`max_cache_memory_usage` has been exceeded. This is to protect hot caches
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# from being emptied while Synapse is evicting due to memory.
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#min_cache_ttl: 5m
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# Controls how long the results of a /sync request are cached for after
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# a successful response is returned. A higher duration can help clients with
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# intermittent connections, at the cost of higher memory usage.
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@ -263,6 +281,21 @@ class CacheConfig(Config):
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)
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self.expiry_time_msec = self.parse_duration(expiry_time)
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self.cache_autotuning = cache_config.get("cache_autotuning")
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if self.cache_autotuning:
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max_memory_usage = self.cache_autotuning.get("max_cache_memory_usage")
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self.cache_autotuning["max_cache_memory_usage"] = self.parse_size(
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max_memory_usage
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)
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target_mem_size = self.cache_autotuning.get("target_cache_memory_usage")
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self.cache_autotuning["target_cache_memory_usage"] = self.parse_size(
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target_mem_size
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)
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min_cache_ttl = self.cache_autotuning.get("min_cache_ttl")
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self.cache_autotuning["min_cache_ttl"] = self.parse_duration(min_cache_ttl)
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self.sync_response_cache_duration = self.parse_duration(
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cache_config.get("sync_response_cache_duration", 0)
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)
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@ -18,6 +18,7 @@ import os
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import re
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from typing import Iterable, Optional, overload
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import attr
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from prometheus_client import REGISTRY, Metric
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from typing_extensions import Literal
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@ -27,52 +28,24 @@ from synapse.metrics._types import Collector
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logger = logging.getLogger(__name__)
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def _setup_jemalloc_stats() -> None:
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"""Checks to see if jemalloc is loaded, and hooks up a collector to record
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statistics exposed by jemalloc.
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"""
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# Try to find the loaded jemalloc shared library, if any. We need to
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# introspect into what is loaded, rather than loading whatever is on the
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# path, as if we load a *different* jemalloc version things will seg fault.
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# We look in `/proc/self/maps`, which only exists on linux.
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if not os.path.exists("/proc/self/maps"):
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logger.debug("Not looking for jemalloc as no /proc/self/maps exist")
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return
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# We're looking for a path at the end of the line that includes
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# "libjemalloc".
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regex = re.compile(r"/\S+/libjemalloc.*$")
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jemalloc_path = None
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with open("/proc/self/maps") as f:
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for line in f:
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match = regex.search(line.strip())
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if match:
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jemalloc_path = match.group()
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if not jemalloc_path:
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# No loaded jemalloc was found.
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logger.debug("jemalloc not found")
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return
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logger.debug("Found jemalloc at %s", jemalloc_path)
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jemalloc = ctypes.CDLL(jemalloc_path)
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@attr.s(slots=True, frozen=True, auto_attribs=True)
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class JemallocStats:
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jemalloc: ctypes.CDLL
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@overload
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def _mallctl(
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name: str, read: Literal[True] = True, write: Optional[int] = None
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self, name: str, read: Literal[True] = True, write: Optional[int] = None
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) -> int:
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...
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@overload
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def _mallctl(name: str, read: Literal[False], write: Optional[int] = None) -> None:
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def _mallctl(
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self, name: str, read: Literal[False], write: Optional[int] = None
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) -> None:
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...
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def _mallctl(
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name: str, read: bool = True, write: Optional[int] = None
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self, name: str, read: bool = True, write: Optional[int] = None
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) -> Optional[int]:
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"""Wrapper around `mallctl` for reading and writing integers to
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jemalloc.
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@ -120,7 +93,7 @@ def _setup_jemalloc_stats() -> None:
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# Where oldp/oldlenp is a buffer where the old value will be written to
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# (if not null), and newp/newlen is the buffer with the new value to set
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# (if not null). Note that they're all references *except* newlen.
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result = jemalloc.mallctl(
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result = self.jemalloc.mallctl(
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name.encode("ascii"),
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input_var_ref,
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input_len_ref,
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@ -136,21 +109,80 @@ def _setup_jemalloc_stats() -> None:
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return input_var.value
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def _jemalloc_refresh_stats() -> None:
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def refresh_stats(self) -> None:
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"""Request that jemalloc updates its internal statistics. This needs to
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be called before querying for stats, otherwise it will return stale
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values.
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"""
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try:
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_mallctl("epoch", read=False, write=1)
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self._mallctl("epoch", read=False, write=1)
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except Exception as e:
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logger.warning("Failed to reload jemalloc stats: %s", e)
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def get_stat(self, name: str) -> int:
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"""Request the stat of the given name at the time of the last
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`refresh_stats` call. This may throw if we fail to read
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the stat.
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"""
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return self._mallctl(f"stats.{name}")
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_JEMALLOC_STATS: Optional[JemallocStats] = None
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def get_jemalloc_stats() -> Optional[JemallocStats]:
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"""Returns an interface to jemalloc, if it is being used.
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Note that this will always return None until `setup_jemalloc_stats` has been
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called.
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"""
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return _JEMALLOC_STATS
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def _setup_jemalloc_stats() -> None:
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"""Checks to see if jemalloc is loaded, and hooks up a collector to record
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statistics exposed by jemalloc.
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"""
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global _JEMALLOC_STATS
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# Try to find the loaded jemalloc shared library, if any. We need to
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# introspect into what is loaded, rather than loading whatever is on the
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# path, as if we load a *different* jemalloc version things will seg fault.
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# We look in `/proc/self/maps`, which only exists on linux.
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if not os.path.exists("/proc/self/maps"):
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logger.debug("Not looking for jemalloc as no /proc/self/maps exist")
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return
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# We're looking for a path at the end of the line that includes
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# "libjemalloc".
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regex = re.compile(r"/\S+/libjemalloc.*$")
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jemalloc_path = None
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with open("/proc/self/maps") as f:
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for line in f:
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match = regex.search(line.strip())
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if match:
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jemalloc_path = match.group()
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if not jemalloc_path:
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# No loaded jemalloc was found.
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logger.debug("jemalloc not found")
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return
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logger.debug("Found jemalloc at %s", jemalloc_path)
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jemalloc_dll = ctypes.CDLL(jemalloc_path)
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stats = JemallocStats(jemalloc_dll)
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_JEMALLOC_STATS = stats
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class JemallocCollector(Collector):
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"""Metrics for internal jemalloc stats."""
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def collect(self) -> Iterable[Metric]:
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_jemalloc_refresh_stats()
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stats.refresh_stats()
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g = GaugeMetricFamily(
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"jemalloc_stats_app_memory_bytes",
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@ -184,7 +216,7 @@ def _setup_jemalloc_stats() -> None:
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"metadata",
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):
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try:
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value = _mallctl(f"stats.{t}")
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value = stats.get_stat(t)
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except Exception as e:
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# There was an error fetching the value, skip.
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logger.warning("Failed to read jemalloc stats.%s: %s", t, e)
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@ -13,6 +13,7 @@
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# limitations under the License.
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import logging
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import math
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import threading
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import weakref
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from enum import Enum
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@ -40,6 +41,7 @@ from twisted.internet.interfaces import IReactorTime
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from synapse.config import cache as cache_config
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from synapse.metrics.background_process_metrics import wrap_as_background_process
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from synapse.metrics.jemalloc import get_jemalloc_stats
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from synapse.util import Clock, caches
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from synapse.util.caches import CacheMetric, EvictionReason, register_cache
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from synapse.util.caches.treecache import TreeCache, iterate_tree_cache_entry
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@ -106,10 +108,16 @@ GLOBAL_ROOT = ListNode["_Node"].create_root_node()
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@wrap_as_background_process("LruCache._expire_old_entries")
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async def _expire_old_entries(clock: Clock, expiry_seconds: int) -> None:
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async def _expire_old_entries(
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clock: Clock, expiry_seconds: int, autotune_config: Optional[dict]
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) -> None:
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"""Walks the global cache list to find cache entries that haven't been
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accessed in the given number of seconds.
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accessed in the given number of seconds, or if a given memory threshold has been breached.
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"""
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if autotune_config:
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max_cache_memory_usage = autotune_config["max_cache_memory_usage"]
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target_cache_memory_usage = autotune_config["target_cache_memory_usage"]
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min_cache_ttl = autotune_config["min_cache_ttl"] / 1000
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now = int(clock.time())
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node = GLOBAL_ROOT.prev_node
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@ -119,11 +127,36 @@ async def _expire_old_entries(clock: Clock, expiry_seconds: int) -> None:
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logger.debug("Searching for stale caches")
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evicting_due_to_memory = False
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# determine if we're evicting due to memory
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jemalloc_interface = get_jemalloc_stats()
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if jemalloc_interface and autotune_config:
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try:
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jemalloc_interface.refresh_stats()
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mem_usage = jemalloc_interface.get_stat("allocated")
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if mem_usage > max_cache_memory_usage:
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logger.info("Begin memory-based cache eviction.")
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evicting_due_to_memory = True
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except Exception:
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logger.warning(
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"Unable to read allocated memory, skipping memory-based cache eviction."
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)
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while node is not GLOBAL_ROOT:
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# Only the root node isn't a `_TimedListNode`.
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assert isinstance(node, _TimedListNode)
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if node.last_access_ts_secs > now - expiry_seconds:
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# if node has not aged past expiry_seconds and we are not evicting due to memory usage, there's
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# nothing to do here
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if (
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node.last_access_ts_secs > now - expiry_seconds
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and not evicting_due_to_memory
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):
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break
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# if entry is newer than min_cache_entry_ttl then do not evict and don't evict anything newer
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if evicting_due_to_memory and now - node.last_access_ts_secs < min_cache_ttl:
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break
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cache_entry = node.get_cache_entry()
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@ -136,10 +169,29 @@ async def _expire_old_entries(clock: Clock, expiry_seconds: int) -> None:
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assert cache_entry is not None
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cache_entry.drop_from_cache()
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# Check mem allocation periodically if we are evicting a bunch of caches
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if jemalloc_interface and evicting_due_to_memory and (i + 1) % 100 == 0:
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try:
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jemalloc_interface.refresh_stats()
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mem_usage = jemalloc_interface.get_stat("allocated")
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if mem_usage < target_cache_memory_usage:
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evicting_due_to_memory = False
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logger.info("Stop memory-based cache eviction.")
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except Exception:
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logger.warning(
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"Unable to read allocated memory, this may affect memory-based cache eviction."
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)
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# If we've failed to read the current memory usage then we
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# should stop trying to evict based on memory usage
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evicting_due_to_memory = False
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# If we do lots of work at once we yield to allow other stuff to happen.
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if (i + 1) % 10000 == 0:
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logger.debug("Waiting during drop")
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await clock.sleep(0)
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if node.last_access_ts_secs > now - expiry_seconds:
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await clock.sleep(0.5)
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else:
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await clock.sleep(0)
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logger.debug("Waking during drop")
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node = next_node
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@ -156,21 +208,28 @@ async def _expire_old_entries(clock: Clock, expiry_seconds: int) -> None:
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def setup_expire_lru_cache_entries(hs: "HomeServer") -> None:
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"""Start a background job that expires all cache entries if they have not
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been accessed for the given number of seconds.
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been accessed for the given number of seconds, or if a given memory usage threshold has been
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breached.
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"""
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if not hs.config.caches.expiry_time_msec:
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if not hs.config.caches.expiry_time_msec and not hs.config.caches.cache_autotuning:
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return
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logger.info(
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"Expiring LRU caches after %d seconds", hs.config.caches.expiry_time_msec / 1000
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)
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if hs.config.caches.expiry_time_msec:
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expiry_time = hs.config.caches.expiry_time_msec / 1000
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logger.info("Expiring LRU caches after %d seconds", expiry_time)
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else:
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expiry_time = math.inf
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global USE_GLOBAL_LIST
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USE_GLOBAL_LIST = True
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clock = hs.get_clock()
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clock.looping_call(
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_expire_old_entries, 30 * 1000, clock, hs.config.caches.expiry_time_msec / 1000
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_expire_old_entries,
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30 * 1000,
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clock,
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expiry_time,
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hs.config.caches.cache_autotuning,
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)
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@ -14,8 +14,9 @@
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from typing import List
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from unittest.mock import Mock
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from unittest.mock import Mock, patch
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from synapse.metrics.jemalloc import JemallocStats
|
||||
from synapse.util.caches.lrucache import LruCache, setup_expire_lru_cache_entries
|
||||
from synapse.util.caches.treecache import TreeCache
|
||||
|
||||
@ -316,3 +317,58 @@ class TimeEvictionTestCase(unittest.HomeserverTestCase):
|
||||
|
||||
self.assertEqual(cache.get("key1"), None)
|
||||
self.assertEqual(cache.get("key2"), 3)
|
||||
|
||||
|
||||
class MemoryEvictionTestCase(unittest.HomeserverTestCase):
|
||||
@override_config(
|
||||
{
|
||||
"caches": {
|
||||
"cache_autotuning": {
|
||||
"max_cache_memory_usage": "700M",
|
||||
"target_cache_memory_usage": "500M",
|
||||
"min_cache_ttl": "5m",
|
||||
}
|
||||
}
|
||||
}
|
||||
)
|
||||
@patch("synapse.util.caches.lrucache.get_jemalloc_stats")
|
||||
def test_evict_memory(self, jemalloc_interface) -> None:
|
||||
mock_jemalloc_class = Mock(spec=JemallocStats)
|
||||
jemalloc_interface.return_value = mock_jemalloc_class
|
||||
|
||||
# set the return value of get_stat() to be greater than max_cache_memory_usage
|
||||
mock_jemalloc_class.get_stat.return_value = 924288000
|
||||
|
||||
setup_expire_lru_cache_entries(self.hs)
|
||||
cache = LruCache(4, clock=self.hs.get_clock())
|
||||
|
||||
cache["key1"] = 1
|
||||
cache["key2"] = 2
|
||||
|
||||
# advance the reactor less than the min_cache_ttl
|
||||
self.reactor.advance(60 * 2)
|
||||
|
||||
# our items should still be in the cache
|
||||
self.assertEqual(cache.get("key1"), 1)
|
||||
self.assertEqual(cache.get("key2"), 2)
|
||||
|
||||
# advance the reactor past the min_cache_ttl
|
||||
self.reactor.advance(60 * 6)
|
||||
|
||||
# the items should be cleared from cache
|
||||
self.assertEqual(cache.get("key1"), None)
|
||||
self.assertEqual(cache.get("key2"), None)
|
||||
|
||||
# add more stuff to caches
|
||||
cache["key1"] = 1
|
||||
cache["key2"] = 2
|
||||
|
||||
# set the return value of get_stat() to be lower than target_cache_memory_usage
|
||||
mock_jemalloc_class.get_stat.return_value = 10000
|
||||
|
||||
# advance the reactor past the min_cache_ttl
|
||||
self.reactor.advance(60 * 6)
|
||||
|
||||
# the items should still be in the cache
|
||||
self.assertEqual(cache.get("key1"), 1)
|
||||
self.assertEqual(cache.get("key2"), 2)
|
||||
|
||||
Loading…
Reference in New Issue
Block a user