Re: OOM detection regressions since 4.7

[Markus Trippelsdorf]

On 2016.08.22 at 11:32 +0200, Michal Hocko wrote:
> 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

For the report [1] above:

markus@x4 linux % cat .config | grep CONFIG_COMPACTION
# CONFIG_COMPACTION is not set

-- 
Markus