Maximal number of timewait sockets held by system simultaneously. If this number is exceeded time-wait socket is immediately destroyed and warning is printed. This limit exists only to prevent simple DoS attacks, you must not lower the limit artificially, but rather increase it (probably, after increasing installed memory), if network conditions require more than default value.
tcp_mem - vector of 3 INTEGERs: min, pressure, max min: 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 “min”.
max: number of pages allowed for queueing by all TCP sockets.
Defaults are calculated at boot time from amount of available memory.source