Fixup autotuning sample config

changelog.d/12760.feature

@@ -0,0 +1 @@
+Add a config options to allow for auto-tuning of caches.

docs/sample_config.yaml

@@ -784,22 +784,33 @@ caches:
   #
   #cache_entry_ttl: 30m
 
-  # This flag enables cache autotuning, and is further specified by the sub-options `max_cache_memory_usage`,
-  # `target_cache_memory_usage`, `min_cache_ttl`. These flags work in conjunction with each other to maintain
-  # a balance between cache memory usage and cache entry availability. You must be using jemalloc to utilize
-  # this option, and all three of the options must be specified for this feature to work.
+  # This flag enables cache autotuning, and is further specified by the
+  # sub-options `max_cache_memory_usage`, `target_cache_memory_usage`,
+  # `min_cache_ttl`. These flags work in conjunction with each other to
+  # maintain a balance between cache memory usage and cache entry
+  # availability. You must be using jemalloc to utilize this option, and
+  # all three of the options must be specified for this feature to work.
+  #
   #cache_autotuning:
-    # This flag sets a ceiling on much memory the cache can use before caches begin to be continuously evicted.
-    # They will continue to be evicted until the memory usage drops below the `target_memory_usage`, set in
-    # the flag below, or until the `min_cache_ttl` is hit.
+    # This flag sets a ceiling on much memory the cache can use before
+    # caches begin to be continuously evicted. They will continue to be
+    # evicted until the memory usage drops below the
+    # `target_memory_usage`, set in the flag below, or until the
+    # `min_cache_ttl` is hit.
+    #
     #max_cache_memory_usage: 1024M
 
-    # This flag sets a rough target for the desired memory usage of the caches.
+    # This flag sets a rough target for the desired memory usage of the
+    # caches.
+    #
     #target_cache_memory_usage: 758M
 
-    # 'min_cache_ttl` sets a limit under which newer cache entries are not evicted and is only applied when
-    # caches are actively being evicted/`max_cache_memory_usage` has been exceeded. This is to protect hot caches
-    # from being emptied while Synapse is evicting due to memory.
+    # 'min_cache_ttl` sets a limit under which newer cache entries are not
+    # evicted and is only applied when caches are actively being
+    # evicted/`max_cache_memory_usage` has been exceeded. This is to
+    # protect hot caches from being emptied while Synapse is evicting due
+    # to memory.
+    #
     #min_cache_ttl: 5m
 
   # Controls how long the results of a /sync request are cached for after

synapse/config/cache.py

@@ -176,22 +176,33 @@ def generate_config_section(self, **kwargs: Any) -> str:
           #
           #cache_entry_ttl: 30m
 
-          # This flag enables cache autotuning, and is further specified by the sub-options `max_cache_memory_usage`,
-          # `target_cache_memory_usage`, `min_cache_ttl`. These flags work in conjunction with each other to maintain
-          # a balance between cache memory usage and cache entry availability. You must be using jemalloc to utilize
-          # this option, and all three of the options must be specified for this feature to work.
+          # This flag enables cache autotuning, and is further specified by the
+          # sub-options `max_cache_memory_usage`, `target_cache_memory_usage`,
+          # `min_cache_ttl`. These flags work in conjunction with each other to
+          # maintain a balance between cache memory usage and cache entry
+          # availability. You must be using jemalloc to utilize this option, and
+          # all three of the options must be specified for this feature to work.
+          #
           #cache_autotuning:
-            # This flag sets a ceiling on much memory the cache can use before caches begin to be continuously evicted.
-            # They will continue to be evicted until the memory usage drops below the `target_memory_usage`, set in
-            # the flag below, or until the `min_cache_ttl` is hit.
+            # This flag sets a ceiling on much memory the cache can use before
+            # caches begin to be continuously evicted. They will continue to be
+            # evicted until the memory usage drops below the
+            # `target_memory_usage`, set in the flag below, or until the
+            # `min_cache_ttl` is hit.
+            #
             #max_cache_memory_usage: 1024M
 
-            # This flag sets a rough target for the desired memory usage of the caches.
+            # This flag sets a rough target for the desired memory usage of the
+            # caches.
+            #
             #target_cache_memory_usage: 758M
 
-            # 'min_cache_ttl` sets a limit under which newer cache entries are not evicted and is only applied when
-            # caches are actively being evicted/`max_cache_memory_usage` has been exceeded. This is to protect hot caches
-            # from being emptied while Synapse is evicting due to memory.
+            # 'min_cache_ttl` sets a limit under which newer cache entries are not
+            # evicted and is only applied when caches are actively being
+            # evicted/`max_cache_memory_usage` has been exceeded. This is to
+            # protect hot caches from being emptied while Synapse is evicting due
+            # to memory.
+            #
             #min_cache_ttl: 5m
 
           # Controls how long the results of a /sync request are cached for after