From ae58ab5c61e2d6798971a60eed99403de070683a Mon Sep 17 00:00:00 2001
From: Joseph Kogut <joseph@balena.io>
Date: Mon, 28 Oct 2024 08:38:33 -0700
Subject: [PATCH] compose: increase zram at runtime

To alleviate memory pressure, increase zram to 50% of total memory at
runtime. This allows the host to compress inactive pages to reduce
contention.

This service optionally allows for the maximum zram percentage and
compression algorithm to be modified at runtime using variables.

Change-type: patch
Signed-off-by: Joseph Kogut <joseph@balena.io>
---
 docker-compose.yml | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/docker-compose.yml b/docker-compose.yml
index 84966bf0..8e721495 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -284,6 +284,48 @@ services:
       CLOUDFLARE_DNS_ZONE: product-os.io
       ROBOT_API: https://robot-ws.your-server.de
 
+  zram:
+    image: docker:27.3.1-cli-alpine3.20
+    restart: no
+    labels:
+      io.balena.features.balena-socket: '1'
+    entrypoint:
+      - /bin/sh
+      - -c
+    environment:
+      ENABLED: true
+      ZRAM_PCT: 50
+      ZRAM_ALGO: lz4
+    command:
+      - |
+        set -e
+        [[ $ENABLED == 'true' ]] || exit
+
+        HOST_CONTAINER_NAME=host-chroot
+        stop_container() { docker stop "$(docker ps -qf "NAME=$HOST_CONTAINER_NAME")"; }
+        trap stop_container EXIT
+
+        host_cmd() {
+          if [ -z "$(docker ps -qf "NAME=$HOST_CONTAINER_NAME")" ]; then
+            docker run \
+              --interactive \
+              --tty=true \
+              --detach \
+              --rm \
+              --name="$HOST_CONTAINER_NAME" \
+              --volume=/:/host \
+              --privileged \
+              alpine:3.20.3
+          fi
+
+          HOST_CONTAINER_ID="$(docker ps -qf "NAME=$HOST_CONTAINER_NAME")"
+          docker exec "$HOST_CONTAINER_ID" chroot /host bash -c "$*"
+        }
+
+        host_cmd "swaps=\$(awk 'NR>1 { print \$1 }' /proc/swaps); if [ -n \"\$swaps\" ]; then swapoff \$swaps; fi"
+        host_cmd "zrams=\$(find /dev -name \"zram*\"); if [ -n \"\$zrams\" ]; then for d in \$zrams; do zramctl -r \$d; done; fi"
+        zram_dev=$(host_cmd "memtotal=\$(grep MemTotal /proc/meminfo | awk '{ print \$2 }'); zramctl --find --size \$((memtotal * $ZRAM_PCT / 100))K --algorithm $ZRAM_ALGO")
+        host_cmd "mkswap $zram_dev && swapon $zram_dev"
   # https://github.com/balenablocks/cert-manager
   # https://certbot.eff.org/docs/using.html
   # https://certbot-dns-cloudflare.readthedocs.io/