Set LD_PRELOAD to load jemalloc in Dockerfile-workers. (#14182)

changelog.d/14182.docker

@@ -0,0 +1 @@
+Set LD_PRELOAD to use jemalloc memory allocator in Dockerfile-workers.

docker/configure_workers_and_start.py

@@ -39,6 +39,7 @@
 # continue to work if so.
 
 import os
+import platform
 import subprocess
 import sys
 from pathlib import Path
@@ -632,14 +633,23 @@ def main(args: List[str], environ: MutableMapping[str, str]) -> None:
         with open(mark_filepath, "w") as f:
             f.write("")
 
+    # Lifted right out of start.py
+    jemallocpath = "/usr/lib/%s-linux-gnu/libjemalloc.so.2" % (platform.machine(),)
+
+    if os.path.isfile(jemallocpath):
+        environ["LD_PRELOAD"] = jemallocpath
+    else:
+        log("Could not find %s, will not use" % (jemallocpath,))
+
     # Start supervisord, which will start Synapse, all of the configured worker
     # processes, redis, nginx etc. according to the config we created above.
     log("Starting supervisord")
-    os.execl(
+    os.execle(
         "/usr/local/bin/supervisord",
         "supervisord",
         "-c",
         "/etc/supervisor/supervisord.conf",
+        environ,
     )