Merge branch 'tcp_mem_pressure'

Eric Dumazet says:

====================
tcp: better handling of memory pressure

When testing commit 790ba456

 ("tcp: set SOCK_NOSPACE under memory
pressure") using edge triggered epoll applications, I found various
issues under memory pressure and thousands of active sockets.

This patch series is a first round to solve these issues, in send
and receive paths. There are probably other fixes needed, but
with this series, my tests now all succeed.

v2: fix typo in "allow one skb to be received per socket under memory pressure",
as spotted by Jason Baron.
====================

Acked-by: Jason Baron <jbaron@akamai.com>
Signed-off-by: David S. Miller <davem@davemloft.net>