Vector of 3 integers: min, pressure, max.
- low - below this number of pages TCP is not bothered about its memory appetite.
- pressure - when amount of memory allocated by TCP exceeds this number of pages, TCP moderates its memory consumption and enters memory pressure mode, which is exited when memory consumption falls under "low".
- high - number of pages allowed for queueing by all TCP sockets.
Defaults are calculated at boot time from amount of available memory.