Only use GLOBAL_LIST if time based eviction is enabled

Author: erikjohnston

synapse/util/caches/lrucache.py

@@ -190,6 +190,10 @@ def get_cache_entry(self) -> Optional[P]:
         return self.cache_entry()
 
 
+# Whether to insert new cache entries to the global list. We only add to it if
+# time based eviction is enabled.
+USE_GLOBAL_LIST = False
+
 # A linked list of all cache entries, allowing efficient time based eviction.
 GLOBAL_ROOT = _ListNode[_CacheEntry]()
 
@@ -247,6 +251,9 @@ def expire_lru_cache_entries_after(hs: "HomeServer"):
     """Start a background job that expires all cache entries if they have not
     been accessed for the given number of seconds.
     """
+    global USE_GLOBAL_LIST
+    USE_GLOBAL_LIST = True
+
     clock = hs.get_clock()
     clock.looping_call(
         _expire_old_entries, 30 * 1000, clock, hs.config.caches.expiry_time_msec / 1000
@@ -275,7 +282,9 @@ def __init__(
     ):
         self_ref = weakref.ref(self, lambda _: self.drop_from_lists())
         self.list_node = _ListNode.insert_after(self_ref, root)
-        self.global_list_node = _ListNode.insert_after(self_ref, GLOBAL_ROOT)
+        self.global_list_node = None
+        if USE_GLOBAL_LIST:
+            self.global_list_node = _ListNode.insert_after(self_ref, GLOBAL_ROOT)
 
         # We store a weak reference to the cache object so that this _Node can
         # remove itself from the cache. If the cache is dropped we ensure we
@@ -304,12 +313,14 @@ def __init__(
                 _get_size_of(key)
                 + _get_size_of(value)
                 + _get_size_of(self.list_node, recurse=False)
-                + _get_size_of(self.global_list_node, recurse=False)
                 + _get_size_of(self.callbacks, recurse=False)
                 + _get_size_of(self, recurse=False)
             )
             self.memory += _get_size_of(self.memory, recurse=False)
 
+            if self.global_list_node:
+                self.memory += _get_size_of(self.global_list_node, recurse=False)
+
     def add_callbacks(self, callbacks: Collection[Callable[[], None]]) -> None:
         """Add to stored list of callbacks, removing duplicates."""
 
@@ -347,7 +358,9 @@ def drop_from_cache(self) -> None:
     def drop_from_lists(self) -> None:
         """Remove this node from the cache lists."""
         self.list_node.remove_from_list()
-        self.global_list_node.remove_from_list()
+
+        if self.global_list_node:
+            self.global_list_node.remove_from_list()
 
 
 class LruCache(Generic[KT, VT]):
@@ -478,7 +491,8 @@ def add_node(key, value, callbacks: Collection[Callable[[], None]] = ()):
 
         def move_node_to_front(node: _Node):
             node.list_node.move_after(list_root)
-            node.global_list_node.move_after(GLOBAL_ROOT)
+            if node.global_list_node:
+                node.global_list_node.move_after(GLOBAL_ROOT)
 
         def delete_node(node: _Node) -> int:
             node.drop_from_lists()