base-files: increase vm.min_free_kbytes

Network drivers typically allocate memory in atomic context. For that to
be reliable, there needs to be enough free memory. Set the value
heuristically based on the total amount of system RAM.

Signed-off-by: Felix Fietkau <nbd@nbd.name>

package/base-files/files/etc/init.d/sysctl

@@ -2,7 +2,23 @@
 # Copyright (C) 2006 OpenWrt.org
 
 START=11
+
+set_vm_min_free() {
+	mem="$(grep MemTotal /proc/meminfo  | awk '{print $2}')"
+	if [ "$mem" -gt 65536 ]; then # 128M
+		val=16384
+	elif [ "$mem" -gt 32768 ]; then # 64M
+		val=8192
+	elif [ "$mem" -gt 16384 ]; then # 32M
+		val=4096
+	else
+		return
+	fi
+	sysctl -qw vm.min_free_kbytes="$val"
+}
+
 start() {
+	set_vm_min_free
 	for CONF in /etc/sysctl.conf /etc/sysctl.d/*.conf; do
 		[ -f "$CONF" ] && sysctl -p "$CONF" -e >&-
 	done