OOM detection regressions since 4.7

[Michal Hocko]

Hi, 
there have been multiple reports [1][2][3][4][5] about pre-mature OOM
killer invocations since 4.7 which contains oom detection rework. All of
them were for order-2 (kernel stack) alloaction requests failing because
of a high fragmentation and compaction failing to make any forward
progress. While investigating this we have found out that the compaction
just gives up too early. Vlastimil has been working on compaction
improvement for quite some time and his series [6] is already sitting
in mmotm tree. This already helps a lot because it drops some heuristics
which are more aimed at lower latencies for high orders rather than
reliability. Joonsoo has then identified further problem with too many
blocks being marked as unmovable [7] and Vlastimil has prepared a patch
on top of his series [8] which is also in the mmotm tree now.

That being said, the regression is real and should be fixed for 4.7
stable users. [6][8] was reported to help and ooms are no longer
reproducible. I know we are quite late (rc3) in 4.8 but I would vote
for mergeing those patches and have them in 4.8. For 4.7 I would go
with a partial revert of the detection rework for high order requests
(see patch below). This patch is really trivial. If those compaction
improvements are just too large for 4.8 then we can use the same patch
as for 4.7 stable for now and revert it in 4.9 after compaction changes
are merged.

Thoughts?

[1] http://lkml.kernel.org/r/20160731051121.GB307@x4
[2] http://lkml.kernel.org/r/201608120901.41463.a.miskiewicz@xxxxxxxxx
[3] http://lkml.kernel.org/r/20160801192620.GD31957@xxxxxxxxxxxxxx
[4] https://lists.opensuse.org/opensuse-kernel/2016-08/msg00021.html
[5] https://bugzilla.opensuse.org/show_bug.cgi?id=994066
[6] http://lkml.kernel.org/r/20160810091226.6709-1-vbabka@xxxxxxx
[7] http://lkml.kernel.org/r/20160816031222.GC16913@js1304-P5Q-DELUXE
[8] http://lkml.kernel.org/r/f7a9ea9d-bb88-bfd6-e340-3a933559305a@xxxxxxx

---