On Mon, 2017-03-13 at 18:34 -0500, Josh Hunt wrote:

In this particular case they really do want to know total # of bytes in 
the receive queue, not the data bytes they can consume from an 
application pov. The kernel currently only exposes this value through 
netlink or /proc/net/udp from what I saw.

I believe Eric's suggestion in his previous mail was to export all of 
these meminfo metrics via a single socket option call similar to how its 
done in netlink. We could then use that for both call sites.

I agree that it would be useful to also have the data you and Eric are 
suggesting exposed somewhere, the total # of skb->len bytes sitting in 
the receive queue. I could add that as a second socket option.

Please note that UDP stack does not maintain a per socket sum(skb->len)

Implementing this in a system call would require to lock the receive
queue (blocking BH) and iterating over a potential huge skb list.

Or add a new socket field and add/sub every skb->len of packets
added/removed to/from receive queue.

So I would prefer to not provide this information, this looks quite a
bloat.