syncthing: add GC and thread control variables

Add Go GC and threading control variables - GOGC, GOMEMLIMIT, and
GOMAXPROCS - to all services to allow more granular control of the
memory management on lower memory devices.

Link: https://go.dev/doc/gc-guide#GOGC
Link: https://pkg.go.dev/runtime#pkg-overview
Link: https://go.dev/blog/container-aware-gomaxprocs
Signed-off-by: George Sapkin <george@sapk.in>

utils/syncthing/files/stdiscosrv.conf

@@ -17,3 +17,16 @@ config stdiscosrv 'stdiscosrv'
 	# option compression '0'
 	# option debug '0'
 	# option http '1'
+
+	# Advanced options. Modify at your own risk.
+
+	# More info: https://go.dev/doc/gc-guide#GOGC
+	# option gc '0'
+
+	# Max number of OS threads to use
+	# 0 to match the number of CPUs (default)
+	# >0 to explicitly specify concurrency
+	# option maxprocs '0'
+
+	# Soft memory limit in MB, 0 to disable
+	# option memlimit '0'

utils/syncthing/files/stdiscosrv.init

@@ -1,4 +1,6 @@
 #!/bin/sh /etc/rc.common
+#
+# shellcheck disable=SC3043 # ash supports local
 
 START=90
 STOP=10
@@ -35,9 +37,12 @@ start_service() {
 	local db_dir="$conf_dir/discovery.db"
 	local db_flush_interval=''
 	local debug=0
+	local gc=0
 	local http=0
 	local key="$conf_dir/key.pem"
 	local listen=':8443'
+	local maxprocs=0
+	local memlimit=0
 	local metrics_listen=''
 	local nice=0
 	local user='syncthing'
@@ -54,6 +59,11 @@ start_service() {
 	procd_open_instance
 
 	procd_set_param command "$PROG"
+
+	[ "$gc" -le 0 ] || procd_append_param env GOGC="$gc"
+	[ "$maxprocs" -le 0 ] || procd_append_param env GOMAXPROCS="$maxprocs"
+	[ "$memlimit" -le 0 ] || procd_append_param env GOMEMLIMIT="$memlimit"
+
 	procd_append_param command --cert="$cert"
 	[ "$compression" -eq 0 ] || \
 		procd_append_param command --compression

utils/syncthing/files/strelaysrv.conf

@@ -27,3 +27,16 @@ config strelaysrv 'strelaysrv'
 	# option debug '0'
 	# option nat '0'
 	# option pprof '0'
+
+	# Advanced options. Modify at your own risk.
+
+	# More info: https://go.dev/doc/gc-guide#GOGC
+	# option gc '0'
+
+	# Max number of OS threads to use
+	# 0 to match the number of CPUs (default)
+	# >0 to explicitly specify concurrency
+	# option maxprocs '0'
+
+	# Soft memory limit in MB, 0 to disable
+	# option memlimit '0'

utils/syncthing/files/strelaysrv.init

@@ -1,4 +1,6 @@
 #!/bin/sh /etc/rc.common
+#
+# shellcheck disable=SC3043 # ash supports local
 
 START=90
 STOP=10
@@ -30,9 +32,12 @@ start_service() {
 	local enabled=0
 	local debug=0
 	local ext_address=''
+	local gc=0
 	local global_rate=''
 	local keys='/etc/strelaysrv'
 	local listen=':22067'
+	local maxprocs=0
+	local memlimit=0
 	local message_timeout=''
 	local nat=0
 	local nat_lease=''
@@ -64,8 +69,12 @@ start_service() {
 	procd_open_instance
 
 	procd_set_param command "$PROG"
-	[ "$debug" -eq 0 ] || \
-		procd_append_param command -debug
+
+	[ "$gc" -le 0 ] || procd_append_param env GOGC="$gc"
+	[ "$maxprocs" -le 0 ] || procd_append_param env GOMAXPROCS="$maxprocs"
+	[ "$memlimit" -le 0 ] || procd_append_param env GOMEMLIMIT="$memlimit"
+
+	[ "$debug" -eq 0 ] || procd_append_param command -debug
 	[ -z "$ext_address" ] || \
 		procd_append_param command -ext-address="$ext_address"
 	[ -z "$global_rate" ] || \

utils/syncthing/files/syncthing.conf

@@ -14,10 +14,6 @@ config syncthing 'syncthing'
 	# "restart": the service has to be stopped/started for those to take effect.
 	option nice '19'
 
-	# 0 to match the number of CPUs (default)
-	# >0 to explicitly specify concurrency
-	option maxprocs '0'
-
 	# More info: https://docs.syncthing.net/users/syncthing.html
 	# option db_delete_retention_interval ''
 	# option db_maintenance_interval ''
@@ -31,3 +27,16 @@ config syncthing 'syncthing'
 	option log_max_old_files '7'
 	# Size in bytes
 	option log_max_size '1048576'
+
+	# Advanced options. Modify at your own risk.
+
+	# More info: https://go.dev/doc/gc-guide#GOGC
+	# option gc '0'
+
+	# Max number of OS threads to use
+	# 0 to match the number of CPUs (default)
+	# >0 to explicitly specify concurrency
+	# option maxprocs '0'
+
+	# Soft memory limit in MB, 0 to disable
+	# option memlimit '0'

utils/syncthing/files/syncthing.init

@@ -1,4 +1,6 @@
 #!/bin/sh /etc/rc.common
+#
+# shellcheck disable=SC3043 # ash supports local
 
 START=90
 STOP=10
@@ -41,6 +43,7 @@ start_service() {
 	local enabled=0
 	local db_delete_retention_interval=''
 	local db_maintenance_interval=''
+	local gc=0
 	local gui_address='http://0.0.0.0:8384'
 	local gui_apikey=''
 	local home='/etc/syncthing'
@@ -49,29 +52,28 @@ start_service() {
 	local log_max_old_files=7
 	local log_max_size=1048576
 	local maxprocs=0
+	local memlimit=0
 	local nice=0
 	local user='syncthing'
 
 	config_load 'syncthing'
 
-	local group=$(id -gn $user)
-
 	[ "$enabled" -gt 0 ] || return 0
 
+	local group=$(id -gn $user)
+
 	mkdir -p "$home"
 	# A separate step to handle an upgrade use case
 	[ -d "$home" ] && chown -R $user:$group "$home"
 
-	# Changes to "niceness"/maxprocs are not picked up either by reload_config
-	# or by restart: the service has to be stopped/started for it to take effect
-	if [ $maxprocs -le 0 ]; then
-		# Default to the number of cores in this case
-		maxprocs=$(grep -c ^processor /proc/cpuinfo)
-	fi
-
 	procd_open_instance
+
 	procd_set_param command "$PROG"
-	procd_set_param env GOMAXPROCS="$maxprocs"
+
+	[ "$gc" -le 0 ] || procd_append_param env GOGC="$gc"
+	[ "$maxprocs" -le 0 ] || procd_append_param env GOMAXPROCS="$maxprocs"
+	[ "$memlimit" -le 0 ] || procd_append_param env GOMEMLIMIT="$memlimit"
+
 	procd_append_param command serve
 	[ -z "$db_delete_retention_interval" ] || \
 		procd_append_param command --db-delete-retention-interval="$db_delete_retention_interval"
@@ -100,6 +102,7 @@ start_service() {
 	procd_set_param respawn
 	procd_set_param stdout 0
 	procd_set_param stderr 1
+
 	procd_close_instance
 }