http://gothub.r4focoma7gu2zdwwcjjad47ysxt634lg73sxmdbkdozanwqslho5ohyd.onion/vrmiguel/bustd
This approach has its up- and downsides. The amount of free RAM that sysinfo reads does not account for cached memory, while MemAvailable in /proc/meminfo does. The sysinfo syscall is one order of magnitude faster, at least according to this kernel patch (granted, from 2015).