[Xenial] Fixes for LP:1647400

[Thadeu Lima de Souza Cascardo]

BugLink: http://launchpad.net/bugs/1647400

These two patches fix the bug reported as tested by the reporter. I
noticed a speedup as well when running the same workload on a VM, that
is,

dd if=/dev/zero of=/dev/null ibs=16k obs=1200M count=2M

on a 1GiB RAM VM.

There were a couple of conflicts that I fixed on both patches to avoid
backporting a lot of cleanup patches.

Michal Hocko (2):
  mm, oom: rework oom detection
  mm: throttle on IO only when there are too many dirty and writeback
    pages

 include/linux/swap.h |   1 +
 mm/backing-dev.c     |  20 ++------
 mm/page_alloc.c      | 133 +++++++++++++++++++++++++++++++++++++++++++++++----
 mm/vmscan.c          |  25 ++--------
 4 files changed, 133 insertions(+), 46 deletions(-)

-- 
2.9.3