From ccf1dc51d7a2f261f91ef8d1442a7ddeccc632b8 Mon Sep 17 00:00:00 2001
From: Mathieu Velten <matmaul@gmail.com>
Date: Tue, 16 Mar 2021 12:32:18 +0100
Subject: [PATCH] Install jemalloc in docker image (#8553)

Co-authored-by: Will Hunt <willh@matrix.org>
Co-authored-by: Erik Johnston <erik@matrix.org>
---
 changelog.d/8553.docker |  1 +
 docker/Dockerfile       |  1 +
 docker/README.md        |  5 +++++
 docker/start.py         | 12 ++++++++++--
 4 files changed, 17 insertions(+), 2 deletions(-)
 create mode 100644 changelog.d/8553.docker

diff --git a/changelog.d/8553.docker b/changelog.d/8553.docker
new file mode 100644
index 0000000000..f99c4207b8
--- /dev/null
+++ b/changelog.d/8553.docker
@@ -0,0 +1 @@
+Use jemalloc if available in docker.
diff --git a/docker/Dockerfile b/docker/Dockerfile
index d619ee08ed..def4501541 100644
--- a/docker/Dockerfile
+++ b/docker/Dockerfile
@@ -69,6 +69,7 @@ RUN apt-get update && apt-get install -y \
     libpq5 \
     libwebp6 \
     xmlsec1 \
+    libjemalloc2 \
  && rm -rf /var/lib/apt/lists/*
 
 COPY --from=builder /install /usr/local
diff --git a/docker/README.md b/docker/README.md
index 7b138df4d3..3a7dc585e7 100644
--- a/docker/README.md
+++ b/docker/README.md
@@ -204,3 +204,8 @@ healthcheck:
   timeout: 10s
   retries: 3
 ```
+
+## Using jemalloc
+
+Jemalloc is embedded in the image and will be used instead of the default allocator.
+You can read about jemalloc by reading the Synapse [README](../README.md)
\ No newline at end of file
diff --git a/docker/start.py b/docker/start.py
index 0d2c590b88..16d6a8208a 100755
--- a/docker/start.py
+++ b/docker/start.py
@@ -3,6 +3,7 @@
 import codecs
 import glob
 import os
+import platform
 import subprocess
 import sys
 
@@ -213,6 +214,13 @@ def main(args, environ):
     if "-m" not in args:
         args = ["-m", synapse_worker] + args
 
+    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,))
+
     # if there are no config files passed to synapse, try adding the default file
     if not any(p.startswith("--config-path") or p.startswith("-c") for p in args):
         config_dir = environ.get("SYNAPSE_CONFIG_DIR", "/data")
@@ -248,9 +256,9 @@ running with 'migrate_config'. See the README for more details.
     args = ["python"] + args
     if ownership is not None:
         args = ["gosu", ownership] + args
-        os.execv("/usr/sbin/gosu", args)
+        os.execve("/usr/sbin/gosu", args, environ)
     else:
-        os.execv("/usr/local/bin/python", args)
+        os.execve("/usr/local/bin/python", args, environ)
 
 
 if __name__ == "__main__":