Re: [patch] mm, oom: make a last minute check to prevent unnecessary memcg oom kills

[Ami Fischman]

On Wed, Mar 18, 2020 at 2:57 AM Michal Hocko <mhocko@xxxxxxxxxx> wrote:
>
> On Tue 17-03-20 12:00:45, Ami Fischman wrote:
> > On Tue, Mar 17, 2020 at 11:26 AM Robert Kolchmeyer
> > <rkolchmeyer@xxxxxxxxxx> wrote:
> > >
> > > On Tue, Mar 10, 2020 at 3:54 PM David Rientjes <rientjes@xxxxxxxxxx> wrote:
> > > >
> > > > Robert, could you elaborate on the user-visible effects of this issue that
> > > > caused it to initially get reported?
> > >
> > > Ami (now cc'ed) knows more, but here is my understanding.
> >
> > Robert's description of the mechanics we observed is accurate.
> >
> > We discovered this regression in the oom-killer's behavior when
> > attempting to upgrade our system. The fraction of the system that
> > went unhealthy due to this issue was approximately equal to the
> > _sum_ of all other causes of unhealth, which are many and varied,
> > but each of which contribute only a small amount of
> > unhealth. This issue forced a rollback to the previous kernel
> > where we ~never see this behavior, returning our unhealth levels
> > to the previous background levels.
>
> Could you be more specific on the good vs. bad kernel versions? Because
> I do not remember any oom changes that would affect the
> time-to-check-time-to-kill race. The timing might be slightly different
> in each kernel version of course.

The original upgrade attempt included a large window of kernel
versions: 4.14.137 to 4.19.91.  In attempting to narrow down the
failure we found that in tests of 10 runs we went from 0/10
failures to 1/10 failure with the update from
https://chromium.googlesource.com/chromiumos/third_party/kernel/+/74fab24be8994bb5bb8d1aa8828f50e16bb38346
(based on 4.19.60) to
https://chromium.googlesource.com/chromiumos/third_party/kernel/+/6e0fef1b46bb91c196be56365d9af72e52bb4675
(also based on 4.19.60)
and then we went from 1/10 failures to 9/10 failures with the
upgrade to
https://chromium.googlesource.com/chromiumos/third_party/kernel/+/a33dffa8e5c47b877e4daece938a81e3cc810b90
(which I believe is based on 4.19.72).

(this was all before we had the minimal repro yielding Robert's
61/100->0/100 stat in his previous email)