FYI, this setting: sysctl -w vm.min_free_kbytes=65536
reserves 64MB RAM for the kernel and drivers. Without this setting an app could request mem until nothing is left, then kernel has no mem anymore to open new network connections, or connect new wireless clients even come to a complete stall.
It does not matter if it is samba or any other app. I have seen things like this with samba before e.g. when a drive acts up drops, and suddenly you copy to routers ram.