net: loopback: set default mtu to 64K

loopback current mtu of 16436 bytes allows no more than 3 MSS TCP
segments per frame, or 48 Kbytes. Changing mtu to 64K allows TCP
stack to build large frames and significantly reduces stack overhead.

Performance boost on bulk TCP transferts can be up to 30 %, partly
because we now have one ACK message for two 64KB segments, and a lower
probability of hitting /proc/sys/net/ipv4/tcp_reordering default limit.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>
defconfig: Enable Advanced TCP Congestion Control

Enable Westwood+, Hamilton-TCP, Vegas & Veno.
Also, set H-TCP as the default. Prime testing conditions for Mobile
Networks show consistently good results from H-TCP.

Research from the Academy of Business in Dąbrowa Górnicza, Poland
suggests that 3G connections deliver IP parameters similar to wired
connections. The study also suggests that further testing be done
on congestion control algorithms designed for fast networks
because of this (YeAH, Highspeed, Hamilton). Similar can likely be
said for even stronger networks (such as HSDPA & LTE). And while I
have yet to find any follow-up report by the same author, testing
with H-TCP has improved throughput on mobile connections
consistently.

From: http://researchwebshelf.com/uploads/91_a_25.pdf
"TCP Congestion Control Algorithms Performance in 3G networks with
moving client" by Maciej Rostanski & Piotr Pikiewicz, 2010

Signed-off-by: Luis Cruz <ljc2491@gmail.com>
ksm: check and skip page, if it is already scanned

On system like Android where most of the process are forked
from parent w/o execve, KSM can scan same page multiple times
in one scan cycle. There is no advantage in scanning same page
multiple times for merging. During testing with Android, it was
observed around 60% pages are skipped for each scan cycle.

Change-Id: I0cf01802f0b4d61fcab92558beb9e1c660dc9a77
Link: http://lkml.kernel.org/r/CAMrOTPgBtANS_ryRjan0-dTL97U7eRvtf3dCsss=Kn+Uk89fuA@mail.gmail.com
Signed-off-by: Pradeep Sawlani <sawlani@amazon.com>

Signed-off-by: Paul Reioux <reioux@gmail.com>
defconfig: Enable KSM_CHECK_PAGE